Mechanical stability of flexible perovskite solar cells: challenges, strategies, and prospects

Abstract

Flexible perovskite solar cells (F-PSCs) have emerged as a transformative photovoltaic technology with exceptional power conversion efficiencies exceeding 25%, lightweight nature, and compatibility with roll-to-roll manufacturing, yet their commercial deployment faces critical challenges due to insufficient mechanical stability under repetitive deformation. This review systematically examines the mechanical failure mechanisms in F-PSCs, including crack propagation, interfacial delamination, and electrode degradation, which are exacerbated by synergistic interactions with environmental factors such as moisture, oxygen, and light. We comprehensively analyze recent advances in enhancing mechanical resilience through multifaceted strategies encompassing grain boundary engineering with low-dimensional phases and molecular additives, interface engineering utilizing specialized monolayers and polymer networks, and bioinspired structural designs informed by natural systems, which collectively mitigate stress concentration, strengthen interfacial adhesion, and enable superior damage tolerance in flexible perovskite photovoltaics. By integrating insights from material design to structural optimization, this review provides a comprehensive framework for addressing mechanical stability challenges in F-PSCs, advancing their potential applications in wearable electronics and portable power sources.

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1. Introduction

The past decade has witnessed unprecedented advances in perovskite solar cells (PSCs), with their power conversion efficiencies (PCEs) now exceeding 27% in single-junction rigid architectures,^1,2 rivaling established silicon photovoltaics. This rapid progress is largely attributed to the exceptional optoelectronic properties of metal halide perovskites (MHPs), which have emerged as innovative and promising semiconductor materials for next-generation optoelectronics.^3–5 MHPs exhibit prominent optoelectronic characteristics such as high absorption coefficients, tunable bandgaps, long carrier diffusion lengths, strong defect tolerance, and facile solution processability.⁶ However, the inherent brittleness and heavyweight nature of conventional rigid substrates, typically glass, severely restrict their application in emerging fields such as wearable electronics, portable power sources, building-integrated photovoltaics, and aerospace systems, where mechanical flexibility, lightweight design and conformability are paramount.^7–9

F-PSCs, fabricated by replacing rigid glass with flexible substrates like polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyimide (PI), or ultrathin metal foils, have emerged as a transformative technology to overcome these limitations.^10–12 These devices offer unique advantages including compatibility with high-throughput, low-cost roll-to-roll (R2R) manufacturing, exceptional power-to-weight ratios, and the ability to conform to curved surfaces.^13,14 These attributes make F-PSCs particularly attractive for emerging applications such as electronic textiles, curved architectural surfaces, and aerospace systems where conventional rigid solar panels cannot be practically implemented. Recent advancements in material design and device engineering have enabled F-PSCs to achieve remarkable PCEs exceeding 25%,^15,16 approaching the performance levels of their rigid counterparts. Notable breakthroughs include the work of Shi et al., who pioneered a systematic design of dual site molecular dipole architectures through comprehensive screening of fluorine terminated organic molecules, enabling F-PSCs to reach a remarkable PCE of 25.47% while enhancing operational stability under illumination.¹⁵ Liang et al. introduced a multi-functionalized molecular design approach using 2-(4-(dibutylamino)-2-hydroxybenzoyl)-benzoic acid (4-BBA) as an additive, which facilitated preferential deposition at critical interfaces and achieved a record 25.30% efficiency (certified 25.13%) for flexible devices, along with superior mechanical durability.¹⁶ Most recently, Chu et al. introduced an Elastic Porous Meniscus (EPM) printing strategy to overcome the island effect and coffee-ring effect in perovskite films.¹⁷ By regulating shear forces, surface tension, and Laplace force, they extended the crystallization window fourfold, achieving highly uniform films that enabled record-breaking flexible devices with 25.54% efficiency (certified 25.44%) at 1.01 cm² scale and 16.39% (certified 15.65%) for 100 cm² modules. These advances underscore the effectiveness of interface engineering and molecular design in pushing the efficiency boundaries of F-PSCs toward commercial viability.

However, despite these impressive efficiency gains, the widespread commercialization of F-PSCs remains significantly hindered by critical challenges in mechanical stability.^18–20 Unlike conventional rigid solar cells, F-PSCs must withstand repeated mechanical deformation while maintaining their structural integrity and photovoltaic performance.^21,22 The intrinsic brittleness of perovskite materials, combined with the multi-layered device architecture comprising materials with vastly different mechanical properties, creates complex failure mechanisms under mechanical stress.^23,24 These challenges are further compounded by the synergistic degradation pathways that emerge when mechanical deformation interacts with environmental factors such as moisture, oxygen, and illumination.^25–28 The mechanical stability of F-PSCs depends on complex interactions between material properties, interfacial adhesion, device architecture, and environmental factors, with typical failure modes including perovskite layer cracking,²⁹ interfacial delamination,³⁰ and accelerated degradation through defect penetration pathways.³¹ These mechanisms not only directly compromise device performance but also significantly reduce operational lifetime, presenting a fundamental challenge for practical applications. Addressing these issues requires a comprehensive understanding of the mechanical behavior across multiple length scales, ranging from atomic level crystal structures to macroscopic device configurations.

Recent research efforts have made significant progress in enhancing the mechanical durability of F-PSCs through innovative approaches at multiple levels. At the material level, strategies including grain boundary engineering, stress-relief additives, and low-dimensional perovskite incorporation have effectively mitigated crack formation and propagation within the active layer.³² Interface engineering approaches utilizing self-assembled monolayers,³³ bifunctional molecular linkers,³⁴ and polymer networks³⁵ have substantially improved adhesion between functional layers, reducing delamination failure. Moreover, biomimetic structural designs inspired by natural systems such as nacre, vertebrate skeletons, and insect cuticles have provided innovative solutions for stress redistribution and damage tolerance.^36–38 These convergent approaches have substantially advanced the mechanical resilience of F-PSCs, demonstrating the feasibility of achieving both exceptional photovoltaic performance and mechanical durability through rational materials design and architectural innovation.

In this review, a comprehensive analysis of the mechanical stability of F-PSCs is provided, focusing on fundamental failure mechanisms, characterization methodologies, and innovative strategies for enhancement. The basic architecture and key components of F-PSCs are first examined, highlighting how material selection and device structure influence mechanical properties. Mechanical failure mechanisms are then systematically analyzed at multiple levels, from individual functional layers to their interfaces, exploring how these failures couple with environmental factors to accelerate degradation. Subsequently, advanced strategies for improving mechanical stability are discussed, including materials engineering, interface modification, and structural design innovations. Finally, perspectives on the remaining challenges and future research directions needed to realize mechanically robust F-PSCs suitable for commercial deployment in diverse applications are presented. Through this comprehensive examination, insights are provided to guide the development of next generation F-PSCs combining high efficiency, exceptional mechanical durability, and long-term operational stability.

2. Basic architecture of F-PSCs

The fundamental architecture of F-PSCs serves as the cornerstone for achieving high performance and mechanical stability. This section delves into the device structures, key components, and material selections that collectively define the efficiency, flexibility, and durability of F-PSCs. Typically fabricated on flexible substrates using low-temperature processing techniques, F-PSCs are designed to meet the demands of bendable and lightweight applications, such as wearable electronics and building-integrated photovoltaics.^39,40 The architecture comprises several critical layers: transparent electrodes, ETL, perovskite light-absorbing layer, HTL, and metal electrodes, each optimized to enhance charge extraction, minimize defects, and withstand mechanical stress.^41,42

2.1 Device structures

The device architecture of F-PSCs serves as the foundational determinant for achieving high photovoltaic performance and robust mechanical stability. The two predominant configurations are the n–i–p (normal) structure and the p–i–n (inverted) structure, which are primarily distinguished by the sequence of charge transport layers and the direction of light incidence. In n–i–p structures, light enters through the ETL side, whereas in p–i–n structures, it enters through the HTL side.^43–45 When implemented on flexible substrates, the selection between these architectures must carefully account for the compatibility and mechanical resilience of each functional layer to withstand repeated bending and deformation.⁴⁰

In the n–i–p configuration, as illustrated in Fig. 1a, the ETL is first deposited onto a transparent electrode (e.g., ITO-coated flexible substrate), followed by the perovskite light-absorbing layer, the HTL, and finally the metal electrode. Conventional ETL materials such as metal oxides (e.g., TiO₂ or SnO₂) typically require high-temperature processing to achieve high crystallinity and optimal electronic properties, but this is fundamentally incompatible with the thermal limits of most flexible polymeric substrates like PET or PEN (which degrade above ∼150 °C).^46,47 To address this, ow-temperature processing techniques have been developed, such as atomic layer deposition⁴⁸ and solution-based synthesis of SnO₂ nanocrystals,⁴⁹ which enable the formation of dense, high-quality ETLs at temperatures ≤100 °C, thereby minimizing substrate damage. However, the intrinsic brittleness of metal oxide ETLs can lead to interfacial stress concentration and microcrack propagation under bending strain, resulting in performance degradation. Recent optimizations, such as incorporating nanocrystalline SnO₂ layers or additive passivation, have significantly improved mechanical robustness.^50,51 Luo et al. demonstrated that F-doping of SnO₂ electron transport layers via NH₄F incorporation significantly reduced interfacial defects and improved energy-level alignment (Fig. 2a and b), resulting in perovskite solar cells with enhanced open-circuit voltage, higher efficiency (22.12%), and superior environmental stability (>80% performance retention after 35 days under thermal and humidity stress).⁵⁰ Similarly, through interfacial passivation with propylammonium chloride (PACl), which forms protective 2D perovskite layers at grain boundaries and interfaces, Fan et al. demonstrated n–i–p structured F-PSCs with an exceptional power conversion efficiency of 22.06% while maintaining impressive mechanical resilience, preserving 89% of their initial performance after 2000 bending cycles at a 5 mm radius (Fig. 2c and d).⁵¹ Additionally, HTL materials like Spiro-OMeTAD or poly[bis(4-phenyl)(2,4,6-triMethylphenyl)aMine] (PTAA), while capable of being doped to enhance conductivity, may introduce long-term stability risks due to hygroscopicity and dopant migration.⁵²

Fig. 1 Typical F-PSC devices with (a) n–i–p architecture and (b) p–i–n architecture. Reproduced under the terms of the Creative Commons Attribution 4.0 International License (CC BY 4.0).⁴³ Copyright 2023, Copyright Li et al.

Fig. 2 (a) The diagram of the SnO₂–NH₄F-based perovskite solar cells and (b) Device performance of SnO₂- andSnO₂–NH₄F-based PSCs. Reproduced with permission.⁵⁰ Copyright 2022, American Chemical Society. (c) J–V curves of the best F-PSCs based PACl and (d) Normalized PCE evolution of the F-PSCs as a function of bending cycles; the devices were bent at a curvature radius of 5 mm. Reproduced with permission.⁵¹ Copyright 2023, American Chemical Society.

In contrast, the p–i–n configuration reverses the layer sequence. The HTL is deposited first onto the transparent electrode, followed by the perovskite layer, the ETL, and the metal electrode.⁵³ This structure often employs HTL materials such as conductive polymers (e.g., poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS)) or inorganic layers (e.g., NiO_x),^54,55 which can be processed at low temperatures, making them highly suitable for flexible substrates. Advanced deposition techniques, such as slot-die coating with optimized binary solvent systems, have enabled the formation of uniform, dense, and defect-free NiO_x films (Fig. 3a and b) that mitigate the “coffee-ring” effect and provide excellent adhesion and flexibility (Fig. 3g–i).⁵⁶ This has resulted in a PCE of 18.8% (13.74 cm²) for devices, and maintaining 87% of their initial PCE after 5000 bending cycles at a 5 mm radius (Fig. 3e and f). The p–i–n structure also exhibits reduced hysteresis and superior environmental stability, attributed to better interfacial compatibility between the HTL and the perovskite layer, which minimizes stress accumulation and non-radiative recombination. For example, Zheng et al. enhanced interfacial compatibility by introducing (2-(3,6-dimethoxy-9H-carbazol-9-yl)ethyl)phosphonic acid (MeO-2PACz) at the perovskite/HTL interface, which reduced trap states and non-radiative recombination, thereby increasing the device PCE from 13.27% to 15.34% while significantly improving stability. Furthermore, the exceptional mechanical durability of flexible p–i–n PSCs is partly due to the organic materials used for the ETL. Fullerene derivatives (e.g., PCBM, C₆₀) are frequently employed because their compliant nature allows them to act as a stress-buffering interlayer.^57,58

Fig. 3 (a) Architecture and cross-section image of the investigated p–i–n solar cells with a structure of PEN|ITO|NiO_x|perovskite|C₆₀:BCP|Ag. (b) Schematic diagram of the slot-die coating process for the deposition of the NiO_x HTL. (c) PCE distribution of 25 pieces NiO_x-target solar cells derived from a 10.0 cm × 10.0 cm substrate (the arrow indicates the slot-die coating direction). (d) and (e) J–V curves of the best-performing devices with a NiO_x layer deposited by slot-die coating, showing aperture areas of: (d) 0.16 cm², and (e) 1.00 cm² and 13.74 cm². (NiO_x–IPA-black; NiO_x-target-red; and NiO_x–H₂O-blue). (f) The normalized PCE of PSMs as a function of bending cycles. (g)–(i) Thermal IR images of PSMs after an applied reverse bias of 8.0 V for 300 s: (g) NiO_x-IPA, (h), NiO_x–H₂O, and (i) NiO_x-target module. The numbers in the center of the image are the highest temperatures on the module surface. Reproduced with permission.⁵⁹ Copyright 2025, Wiley-VCH.

Overall, n–i–p and p–i–n architectures each present distinct advantages and limitations in F-PSC development. While n–i–p structures demonstrate marginally higher power conversion efficiencies, p–i–n configurations excel in mechanical stability and processing compatibility. The optimal device architecture is inherently context-dependent, necessitating a nuanced approach that aligns with specific application requirements.

2.2 Key components and material selection for F-PSCs

The photovoltaic performance and mechanical resilience of F-PSCs are fundamentally governed by the design and material selection of their core components. This section systematically elaborates on flexible substrates, transparent conductive electrodes, perovskite light-absorbing layers, charge transport layers, and back electrodes, with a focus on how material properties regulate device efficiency, flexibility, and long-term durability. Optimizing these components to achieve synergistic compatibility is critical for advancing high-performance F-PSCs, laying the foundation for subsequent discussions on mechanical characterization and stability enhancement strategies.

2.2.1 Flexible substrates. Flexible substrates constitute the foundational mechanical platform for F-PSCs, necessitating a critical balance between flexural compliance, thermal stability, moisture/oxygen barrier performance, optical transparency, and processing compatibility. The substrate selection directly governs the maximum permissible processing temperature and the device's resilience against environmental degradation. Common substrate materials include PET, PEN, ultrathin glass, metal foils (e.g., Ti, Cu), and biodegradable alternatives like nanocellulose paper.^41,60 PET and PEN are widely adopted due to their low cost, lightweight nature, and high optical transparency. However, their limited thermal stability (PET <150 °C, PEN <200 °C) restricts high-temperature processes such as TiO₂ annealing (>450 °C). Ultrathin glass substrates offer superior thermal stability (up to 700 °C) and ultralow water vapor transmission rate (WVTR) but suffer from inherent brittleness and higher costs.⁶¹ Metal foils (e.g., Ti, Cu) exhibit superior thermal tolerance (withstanding temperatures up to 1000 °C), exceptional electrical conductivity, ductility, and malleability, enabling their dual functionality as both substrate and electrode, thereby simplifying manufacturing processes.^62,63 However, their inherent opacity necessitates specialized top-illumination device architectures, while micron-scale surface roughness compromises device yield and reliability due to increased leakage currents and susceptibility to shorts. Additionally, achieving smooth surfaces requires costly post-processing, and the absence of highly conductive, flexible transparent top electrodes remains a significant challenge.⁶⁴

Emerging biodegradable substrates such as nanocellulose paper offer eco-friendliness, low cost, and mechanical resilience, though they face challenges in barrier performance (high WVTR) and mechanical strength.^65–67 For instance, Gao et al. developed acrylic resin-coated nanocellulose paper (NCP) substrates, achieving a PCE of 4.25% and retaining >80% efficiency after 50 bending cycles, demonstrating robust mechanical flexibility (Fig. 4).⁶⁵ Zhu et al. utilized bamboo-derived cellulose nanofiber substrates to set a record 11.68% PCE for biomass-based F-PSCs, with >70% efficiency retention after 1000 bends at a 4 mm radius, highlighting exceptional durability.⁶⁶Table 1 succinctly encapsulates the key characteristics and enhancement approaches for major flexible substrate categories, including polymer-based materials, ultrathin glass, metal foils, and biodegradable options.

Fig. 4 (a) Preparation process of NCP-based substrate and NCP-based PSCs. (b) Current density–voltage (J–V) characterization of MAPbI₃ devices. (c) Normalized PCE-bending cycles characterization. Inset: A digital photograph of bending state by hand on a glass bottle with a diameter of 15 mm. Reproduced under the terms of the Creative Commons Attribution 4.0 International License (CC BY 4.0).⁶⁵ Copyright 2019, Copyright Gao et al.

Table 1 Overview of flexible substrate materials for F-PSCs

Material category	Representative examples	Core properties	Optimization strategies
Polymer substrates	PET,^60 PEN^41	Low cost, lightweight, high optical transparency, but limited thermal stability (PET <150 °C, PEN <200 °C)	Multilayer barrier coatings
Ultrathin glass	Corning willow glass^68	Superior thermal stability, but inherent brittleness and higher costs	Lamination with polymers
Metal foils	Ti, Cu, Al foils^69	Exceptional thermal tolerance, high electrical conductivity/ductility, but surface roughness causes leakage currents	Passivation layers to prevent metal diffusion
Biodegradable substrates	Nanocellulose paper^65–67	Eco-friendly, but poor barrier properties (high WVTR) and mechanical strength	Resin hybridization for mechanical reinforcement

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2.2.2 Transparent conductive electrodes. Transparent conductive electrodes (TCEs) function as the front contact for charge collection, demanding a combination of high optical transmittance, low sheet resistance, and mechanical flexibility. Traditional transparent conductive oxides like ITO are widely used for their high conductivity and transparency, but suffer from inherent brittleness that induces microcracking under mechanical bending, ultimately leading to device failure, compounded by indium scarcity and high production costs.^70,71

Researchers have turned to alternative materials such as silver nanowires (AgNWs), graphene, carbon nanotubes (CNTs), and conductive polymers to address the limitations of conventional transparent conductive oxides. Among these, AgNWs networks have emerged as highly promising for high-performance F-PSCs, offering high optical transmittance and low sheet resistance through scalable solution-based processing.^72,73 Their mechanical superiority is enhanced by bioinspired engineering approaches, such as polydopamine-welded nanowire junctions, which enable robust electrical recovery under extreme mechanical deformation. Hybridization with conductive polymers further optimizes performance, achieving high PCEs while maintaining excellent transmittance. Notably, Chen et al. demonstrated a flexible ITO-free electrode composed of a 1D and 2D composite structure combining AgNWs and Ti₃C₂T_x MXene nanosheets (Fig. 5a).⁷⁴ The MXene nanosheets functioned as a conductive layer that filled voids within the AgNW network and welded wire-wire junctions via capillary force, significantly reducing contact resistance and enhancing interfacial adhesion with substrates (Fig. 5b–d). This approach effectively mitigated challenges related to random stacking and loose contacts in AgNW electrodes.

Fig. 5 (a) Schematic of the Ti₃C₂T_x MXene and the fabrication procedure of AgNW:MXene flexible transparent conductive electrodes. (b) Resistance changes of AgNW–PET, AgNW:MXene and ITO–PET FTEs at various curvature radii (10, 7.5, 6, 5, and 2.5 mm). (c) and (d) Resistance changes of AgNW–PET, ITO–PET, and AgNW:MXene FTEs under a curvature radius of 5 mm versus the bending times. Reproduced with permission.⁷⁴ Copyright 2022, Royal Society of Chemistry.

Graphene is increasingly recognized as an ideal candidate for flexible transparent electrodes due to its exceptional properties, including high transparency, ultra-high carrier mobility, excellent chemical stability, and mechanical durability. Its conductivity can be enhanced through layer stacking and chemical doping, though a trade-off exists between electrical conductivity and optical transmittance when increasing layer count. For instance, AuCl₃-doped graphene with PEDOT:PSS achieved a PCE of 17.4% in F-PSCs, and retain 90% PCE after 100 bending cycles (radii ≥4 mm).⁷⁵ However, conventional graphene synthesis via chemical vapor deposition (CVD) on catalytic metals necessitates transfer to target substrates, which often introduces contamination and weak adhesion due to van der Waals interactions, leading to delamination under mechanical stress. To mitigate these issues, Wu et al. developed a hybrid electrode (GN-A-P) by integrating graphene with AgNWs on a polymer substrate.⁷⁶ Graphene's 2D structure enhances the electrical conductivity of the hybrid film while protecting AgNWs from degradation due to its high chemical and thermal stability. Similarly, Yang et al. PI/graphene stack that enabled an ultra-clean graphene surface and improved interfacial adhesion through bifunctional groups (–CF₃/–SO²⁻) (Fig. 6a and b).⁷⁷ This structure demonstrated exceptional mechanical durability, maintaining performance stability during up to 10 000 bending cycles (Fig. 6c and d).

Fig. 6 (a) Molecular structure of PAA and PI. (b) Schematic describing the two-step fabrication process of PI@GR. (c)–(e) Mechanical properties and durability of the graphene-based electrode. Reproduced with permission.⁷⁷ Copyright 2020, American Chemical Society.

Conductive polymers, particularly PEDOT:PSS, have emerged as promising candidates for flexible transparent electrodes owing to their solution processability, high transparency, and intrinsic mechanical flexibility.^78–80 However, the widespread adoption of pristine PEDOT:PSS has been hampered by its relatively low electrical conductivity, hygroscopic nature, and inadequate electron-blocking capability, which compromise both efficiency and operational stability of devices.⁸¹ To address these limitations, significant efforts have been devoted to enhancing the performance of PEDOT:PSS-based electrodes. For instance, post-treatment with strong acids can improve conductivity by four orders of magnitude, while molecular modifications suppress moisture ingress. To overcome these challenges, several effective strategies have been developed. For instance, post-treatment with strong acids has been shown to enhance the conductivity by up to four orders of magnitude.^82,83 Hybrid architectures, such as the combination of PEDOT:PSS with Ag mesh, have also been employed to improve both electrical conductivity and mechanical robustness.⁸⁴ These advances highlight the potential of modified PEDOT:PSS electrodes as a competitive option for high-performance, flexible optoelectronic devices.

2.2.3 Perovskite light-absorbing layer. The perovskite light-absorbing layer in F-PSCs typically adopts an ABX₃ structure, such as MAPbI₃, FAPbI₃, CsPbI₃ or mixed-cation compositions.^85–88 These active materials are predominantly deposited via solution-based methods including spin-coating, blade coating⁸⁹ or inkjet printing.⁹⁰ However, the inherent thermal instability of flexible polymer substrates introduces significant processing constraints. Specifically, PET and PEN, with glass transition temperatures of approximately 78 °C and 120 °C respectively, require low-temperature annealing processes (usually less than 100 °C) to prevent detrimental substrate deformation, shrinkage, or reduced optical transparency that occurs above these thermal thresholds.^84,91–93

To overcome these temperature limitations, researchers have developed several innovative low-temperature processing strategies. The two-step spin-coating approach involves initial deposition of a yellow lead iodide (PbI₂) precursor dissolved in DMF/DMSO solvent mixtures, followed by spin-coating organic salts such as MAI or FAI in isopropanol, enabling effective perovskite formation at temperatures below 100 °C.⁹⁴ Alternatively, vapor deposition techniques utilizing co-evaporation of perovskite precursors eliminate the need for thermal annealing entirely while producing highly uniform films and preserving electrode integrity on ultrathin flexible substrates.⁹⁵ Additive engineering approaches demonstrate remarkable effectiveness, as exemplified by Yao et al.'s incorporation of 0D Cs₄Pb(IBr)₆ additives into all-inorganic CsPbI_3−xBr_x perovskites, which converts tensile stress to compressive stress within the film, preventing crack propagation while simultaneously enhancing crystallinity and passivating defects at grain boundaries (Fig. 7a-b).⁴² This multifunctional strategy achieves exceptional mechanical durability with CsPbI_2.81Br_0.19 flexible devices maintaining over 97% of their initial efficiency after 60 000 bending cycles at a 5 mm radius, while delivering impressive power conversion efficiencies up to 14.25% (Fig. 7c–g).

Fig. 7 (a) Schematic-depiction of the formation processes for the Cs₄Pb(IBr)₆-CsPbI_3−xBr_x films and flexible solar cell. (b) Schematic illustration of the stress release mechanisms of pure 3D perovskite and 0D/3D perovskite models during the bending process. (c)–(g) Stability of 0D additive for flexible all-inorganic perovskite solar cells. Reproduced with permission.⁸⁸ Copyright 2023, Wiley-VCH.

Beyond thermal processing considerations, mechanical stability enhancements focus primarily on interfacial and grain boundary engineering strategies. Grain boundary “patching” techniques employ transfer imprinting of alkylammonium halides, including benzenebutanammonium iodide, to form homogeneous two-dimensional perovskite capping layers on three-dimensional films (Fig. 8a and b).⁹⁶ This structural modification substantially reduces crack propagation during mechanical deformation, allowing devices to retain over 80% of their initial efficiency even after 10 000 bending cycles at a 3 mm bending radius (Fig. 8d). Complementary approaches utilize polydimethylsiloxane (PDMS) nanocone coatings applied directly to flexible substrates, simultaneously enhancing light management through improved optical coupling while providing effective stress dissipation that maintains substrate flatness during bending operations, significantly improving overall device robustness under mechanical stress.⁹⁷ These collective innovations in low-temperature processing and mechanical enhancement strategies enable high-quality perovskite films on thermally sensitive flexible substrates while ensuring exceptional mechanical resilience under repeated deformation cycles.

Fig. 8 (a) Schematic diagrams of the fabrication procedures and TOF-SIMS of the perovskite films. (b) and (c) TOF-SIMS of depth profiles for PhBA⁺ (in green) in SCAG (b) and TIAG (c) perovskite films. (d) Photovoltaic performance and mechanical stability of the F-PSCs. Reproduced with permission.⁹⁶ Copyright 2023, American Chemical Society.

2.2.4 Charge transport layers. Charge transport layers (CTLs), comprising ETLs and HTLs, are pivotal for efficient charge separation, extraction, and minimizing recombination losses in F-PSCs. ETLs must exhibit high electron mobility, suitable energy band alignment with perovskites, and compatibility with low-temperature processing (<150 °C) to avoid thermal damage to flexible substrates (such as PET or PEN).^98–100

SnO₂ is a preferred ETL due to its low annealing temperature (∼150 °C), favorable conduction band alignment, and high electron mobility. However, commercial SnO₂ colloidal solutions suffer from precipitation-induced flocculation, leading to interfacial defects and performance degradation. Interfacial engineering strategies like histamine diiodate (HADI) modification optimize energy band alignment (Fig. 9a and b), suppress recombination, and achieve record efficiencies of 22.44% in F-PSCs with >90% retention after 1000 bending cycles.¹⁰¹ TiO₂ requires high-temperature annealing (>450 °C), limiting its use in F-PSCs. Wu et al. developed low-temperature alternatives including magnetron sputtering and UV-treated TiO₂ nanopillars, which enhance film uniformity and yield 13.3% efficiency with 92% retention after 500 bending cycles (Fig. 9d and e).¹⁰² ZnO offers excellent electron mobility but reacts with perovskites, accelerating degradation. Xu et al. demonstrated that surface sulfidation or additives like formamidine disulfide dihydrochloride (FADD) passivate defects, improving PCE to 13.47% and maintaining 83% efficiency after 6000 bending cycles (Fig. 9f and g).¹⁰³

Fig. 9 (a) Adsorption geometries of N in tail NH₃ of HADI at Sn⁴⁺, reactive oxygen species, and hydroxyl groups on the SnO₂ surface, respectively. (b) Adsorption geometries of C=N in the imidazole ring of HADI at Sn⁴⁺, reactive oxygen species, and hydroxyl groups on the SnO₂ surface, respectively. (c) The flexible device structure. (d) J–V curves of champion HADI-based F-PSCs. (e) Normalized PCEs of the flexible device as a function of bending cycles with a fixed bending radius, R = 5 mm. Reproduced with permission.¹⁰¹ Copyright 2022, Wiley-VCH. (f) J–V curves of the control and FADD-modified f-PeSCs. (g) The normalized PCE of the control and FADD-modified f-PeSCs after bending for 1000 cycles with different curvature radii. (h) The normalized PCE of the control and FADD-modified f-PeSCs in bending tests with a curvature of 5 mm. Reproduced with permission.¹⁰² Copyright 2021, Wiley-VCH.

The common materials used for HTLs include Spiro-OMeTAD, PTAA, PEDOT:PSS, and NiO_x. For HTLs to perform optimally, they must exhibit high hole mobility, mechanical flexibility, and stability under bending stress. Spiro-OMeTAD typically requires dopants such as lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) to enhance its conductivity.¹⁰⁴ However, the hygroscopic nature of lithium ions can lead to aggregation, which degrades stability. To mitigate this issue, alternative dopants like F4-TCNQ have been explored, as they improve hygrophobicity and help slow water ingress, although there are still trade-offs in efficiency.¹⁰⁵

PTAA stands out for its superior energy band alignment and mechanical flexibility, but it often suffers from poor wettability, resulting in interfacial defects.^106,107 To address this issue, enhancements using zeolitic imidazolate frameworks (ZIF-67) or pentylammonium acetate (PenAAc) have been implemented, demonstrating effectiveness in improving adhesion and passivating defects. For example, Gao et al. demonstrated that PenAAc modification at the perovskite/PTAA interface enhances device performance through dual-functional passivation, with PenA⁺ cations and Ac-anions binding to surface defects (Fig. 10a–d).¹⁰⁸ This interfacial engineering improved wettability and charge extraction, yielding flexible devices with a certified efficiency of 23.35% and remarkable mechanical stability, maintaining 91% performance after 5000 bending cycles.

Fig. 10 (a) Sematic illustration of the bottom perovskite/PTAA interface. (b) J–V curves of flexible PSCs with different passivators. (c) PCE variance of flexible PSCs (0.08 cm²) during mechanical bending test with different curvature radius. (d) Efficiency evolution of flexible PSCs (0.08 cm²) as a function of mechanical bending cycles at a curvature radius of 4 mm. Reproduced with permission.¹⁰⁸ Copyright 2023, Wiley-VCH. (e) J–V curves of the CAP-containing F-PSCs under the forward and reverse scans. (f) and (g) Device performance of CAP-containing F-PSCs. Reproduced with permission.¹⁰⁹ Copyright 2024, Wiley-VCH.

NiO_x offers high hole mobility and stability, yet low-temperature sol–gel processing often yields defective films.^110,111 To address this, Lian et al. developed a UV irradiation strategy that allows for the fabrication of amorphous, dopant-free NiO_x films at low temperatures, achieving champion efficiencies of 19.7% for flexible perovskite solar cells.¹¹² Ma et al. further investigated current stability issues at maximum power point, revealing that NiO_x with different Ni vacancy concentrations affects ion migration at the buried interface (Fig. 10e–g).¹⁰⁹ By incorporating capsaicin into the perovskite precursor, they successfully stabilized current output during operation while achieving high device efficiency, demonstrating that interfacial crystallization control is critical for stable performance.

Self-assembled monolayers (SAMs) have emerged as promising alternatives to HTL materials, such as PEDOT:PSS and PTAA, by effectively addressing their limitations.^113,114 SAM layers provide uniform coverage and enhance nucleation dynamics at interfaces. A notable example is the integration of NiO_x nanoparticles between sputtered NiO_x and SAM layers, which significantly improves perovskite film uniformity and results in an impressive efficiency of 21.97%.¹¹⁵ In addition to these advancements in HTLs, innovative strain-relief strategies have been developed to tackle mechanical instability issues. For instance, Zheng et al. demonstrated that pre-embedding formammonium (HCOONH₄) additives into the SnO₂ ETL effectively alleviates microstrain and residual strain within the perovskite layer.¹¹⁶ This approach allows F-PSCs to retain 90% of their initial PCE even after 4000 bending cycles, showcasing the potential for improved durability and performance in flexible solar technologies.

2.2.5 Back electrodes. Metal electrodes, such as silver (Ag), gold (Au), and copper (Cu), serve as back contacts in flexible perovskite solar cells, providing essential high conductivity and mechanical compatibility.^117–119 However, their intrinsic rigidity can create interfacial stress, potentially leading to delamination under bending conditions. To address this challenge, Metal foils and carbon-based electrodes have been developed. Metal foils, such as Ti foils, function not only as substrates but also as electrodes, taking advantage of their high ductility and thermal tolerance. For instance, mesoporous-structured F-PSCs on Ti foils maintain their initial PCE across various curvatures after bending tests.⁶³

On the other hand, carbon-based electrodes, including CNTs and graphene, offer superior flexibility, stability, and cost-effectiveness.^120,121 Devices that utilize all-carbon electrodes can retain over 84% of their initial PCE after 2000 bending cycles with a 4 mm radius (Fig. 11).¹²² Specifically, single-walled CNT (SWCNT) electrodes achieve PCEs above 18% with minimal hysteresis and maintain 85% of their initial performance after 1000 bends with a 6 mm radius.⁴¹ Graphene electrodes are known for their atomic-level ultra-flexibility; for example, bilayer graphene on PET substrates exhibits a PCE of 11.9% and retains 90% of performance after 1000 hours at 60 °C or under 1-sun illumination.

Fig. 11 (a) Schematic illustration for CNT/GR-based devices. (b) SEM and TEM images of CNT-based and CNT/GR-based anodes (inset: optical images of CNT-based and CNT/GR-based anodes). (c) Bending durability of AC-F-PSC devices for 4000 bending cycles at 4 mm. Reproduced with permission.¹²² Copyright 2023, American Chemical Society.

Additionally, hybrid or composite electrodes provide a balance between conductivity and mechanical durability. For instance, AgNWs can offer 80–90% transmittance along with low sheet resistance, but they are susceptible to oxidation and poor adhesion. GN-A-P can reduce sheet resistance to 8.06 Ω sq⁻¹, minimize J–V hysteresis, and sustain performance after repeated bending due to the protective barrier effect of graphene.⁷⁶ Furthermore, AZO/AgNWs/AZO composite electrodes exhibit 88.6% transmittance and retain about 98% of their PCE after approximately 600 bending cycles with a 12.5 mm radius.⁴⁸ While carbon electrodes are advantageous for their flexibility, a notable limitation remains their lower conductivity compared to metal electrodes, which poses a challenge for achieving high-efficiency F-PSCs.¹²²

3. Mechanical failure mechanisms in F-PSCs

The commercial viability of flexible F-PSCs faces critical challenges stemming from insufficient mechanical stability. Under repetitive deformation conditions such as bending and stretching, functional layers (including the perovskite active layer, charge transport layers, and electrodes) are susceptible to various mechanical failures including cracking, delamination, and interfacial degradation. These structural failures not only directly compromise device integrity and efficiency but also create pathways for environmental factors (moisture and oxygen ingress), generating synergistic degradation mechanisms that dramatically accelerate performance deterioration. A comprehensive understanding of these mechanical failure mechanisms is therefore essential for developing F-PSCs that simultaneously achieve high efficiency and long-term reliability under real-world operating conditions.

3.1 Failure of functional layers

Flexible perovskite solar cells encounter mechanical stability challenges primarily arising from the failure of functional layers (including the perovskite layer, electrode layers, and charge transport layers) under bending, stretching, or thermal stress conditions. These failure modes encompass crack formation, delamination, defect generation, and the coupling of multiple degradation pathways, collectively leading to efficiency decline and reduced operational lifetime. This section elucidates the fundamental mechanical failure mechanisms in F-PSCs with particular emphasis on emerging insights into stress-induced degradation pathways.

3.1.1 Mechanical failures in perovskite light-absorbing layer. The perovskite layer, serving as the photoactive component, primarily exhibits mechanical failure through crack propagation and grain boundary fracture, resulting from the combined effects of residual stress and external strain.¹²³ These stresses originate from multiple sources. First, the crystallization process itself generates intrinsic stress as the amorphous precursor transforms into a crystalline film. This phase transformation, constrained by the substrate, creates tensile or compressive stress within the film.²³ Notably, flexible substrates (such as PET and PEN) typically present greater surface roughness compared to rigid substrate, further exacerbating localized stress concentration during perovskite film formation.²⁴

During fabrication, thermal annealing induces residual stress due to thermal expansion coefficient mismatches between the perovskite layer and substrate.¹²⁶ Plastic substrates (such as PET and PEN) with low thermal conductivity cause delayed heat transfer, resulting in spatial compositional heterogeneity and residual strain in the perovskite film during the annealing process (Fig. 12a and b).¹²⁴ GIXRD studies reveal gradient strain distributions along the depth direction of perovskite films, with larger strain in the top region prone to crack initiation (Fig. 12c–f).¹²⁵ Furthermore, experimental evidence confirms that when tensile strain exceeds 2.5%, grain boundary cracks emerge in the perovskite layer, causing short-circuit current density (J_sc) to decrease from 25 mA cm⁻² to 12.5 mA cm⁻² with significant fill factor (FF) reduction (Fig. 12g–h).²⁹ These cracks not only compromise film integrity but also accelerate ion migration and defect formation, thereby reducing device efficiency.

Fig. 12 Heat-transfer behavior on perovskite growth and composition distribution: annealing process on (a) glass and (b) plastic substrates. Reproduced with permission.¹²⁴ Copyright 2023, American Chemical Society. (c) GIXRD spectrum at a depth of 50 nm with different tilt angles for the perovskite coated on a flat flexible substrate (RS-PVK). (d) The gradient strain of perovskite layers, where the top surface has the highest residual strain. (e) GIXRD at a depth of 50 nm with different tilt angles for SF-PVK. (f) Schematic drawing showing the perovskite structure with (RS-PVK) and without (SF-PVK) gradient strain. Reproduced under the terms of the Creative Commons Attribution 3.0 International License (CC BY 3.0).¹²⁵ Copyright 2022, Copyright He et al. (g) The simulation J–V curves of F-PSCs under tensile strains from 0% to 2.5%; (h) The terminal current density as a function of the tensile strain under the scanning voltages of 0.1 V, 0.2 V, 0.3 V and 0.6 V. Reproduced under the terms of the Creative Commons Attribution 3.0 International License (CC BY 3.0).²⁹ Copyright 2021, Copyright Kosar et al.

Beyond well-established mechanical failures, recent investigations have uncovered critical degradation pathways operating under real-world conditions. Force-optoelectronic coupling studies have established quantitative relationships between mechanical strain and device performance, revealing that at just 4% tensile strain, power conversion efficiency decreases by approximately 70%, while at 7% strain, transparent electrode resistance increases 150-fold, rendering devices non-functional.¹²⁷ Even subtle deformation induces bandgap modulation (from 1.554 eV to 1.575 eV), affecting light absorption before visible mechanical failure occurs. More recently, Li et al. revealed a previously overlooked mechanism of photomechanically induced decomposition in which perovskite materials undergo significant lattice expansion (>1%) under illumination.¹²⁸ This photostrictive effect generates substantial dynamic stress at grain boundaries during day-night cycling, accelerating defect formation and material decomposition at interfaces. These findings collectively emphasize that conventional testing protocols may underestimate real-world degradation mechanisms, highlighting the necessity of considering both electrical performance metrics and photomechanical effects when designing robust flexible perovskite systems.

3.1.2 Mechanical failures in electrode layers. Electrode layers, particularly transparent conductive oxides such as ITO, exhibit mechanical failure primarily manifested as cracking and resistance escalation under mechanical stress. These failure mechanisms stem from fundamental material property mismatches and processing considerations that limit device flexibility and durability.

Comparative studies of ITO on different flexible substrates reveal substrate-dependent mechanical behaviors. ITO deposited on PET substrates develops cracks at bending radii below 8 mm, with corresponding significant resistance increases (Fig. 13a–c).¹²⁹ These ITO fractures constitute a primary efficiency degradation mechanism as they increase series resistance and diminish charge collection efficiency.⁴¹ Finite element simulations utilizing neutral plane models demonstrate that stress concentration within electrode layers leads to delamination and functional failure. For instance, devices employing commercial adhesives such as DELO exhibit electrode delamination after 3000 bending cycles, resulting in complete efficiency loss (Fig. 13d).¹³⁰

Fig. 13 (a) Strain of ITO films on PET and CPI substrates with decreasing bending radius. Pictures showing bending tests of samples connected to a LED: (b) ITO/PET, (c) ITO/CPI. Reproduced with permission.¹²⁹ Copyright 2017, Elsevier. (d) PCE decay of the NP-F-PSCs with different adhesives at a radius of 4 mm. Reproduced with permission.¹³⁰ Copyright 2025, Wiley-VCH.

These mechanical limitations of conventional electrode materials necessitate the development of alternative approaches, including both novel flexible electrode materials (as discussed in Section 2.2.2) and interface engineering strategies that can effectively accommodate mechanical stress while maintaining functional integrity throughout extended operational lifetimes.

3.1.3 Mechanical failures in charge transport layers. The ETL and HTL exhibit distinctive mechanical failure modes, primarily manifested as film fracture and interfacial delamination resulting from interlayer stress mismatch and insufficient adhesion. Under mechanical deformation, SnO₂ ETLs are particularly susceptible to crack formation, substantially compromising charge extraction efficiency. Similarly, HTLs such as PEDOT:PSS demonstrate significant vulnerability to fracture under tensile strain conditions, attributed to their relatively high Young's modulus and consequent inability to accommodate repetitive bending cycles.¹³¹ These mechanical failures substantially exacerbate non-radiative recombination processes, resulting in measurable reductions in V_oc and FF.¹³² Conversely, strategic interface engineering approaches, such as incorporating a multifunctional zwitterionic crosslinker (MZ) into SnO₂ ETLs, effectively mitigate interfacial stress and enhance mechanical resilience while simultaneously achieving remarkable device efficiencies of 23.94% (Fig. 14a–f).¹²⁴

Fig. 14 (a) Synthetic route of MZ. (b) ESP profile of MZ. (c) Schematic of the MZ-assisted PbI₂ film and perovskite film growth. (d) J–V curves of the F-PSCs under AM1.5G and 100 mW cm⁻² illumination. Inset: Device structure of the F-PSCs. (e) EQE spectra of the flexible devices. (f) Statistics of the device areas and the PCE values obtained from the recently reported high-performance F-PSCs. Reproduced with permission.¹²⁴ Copyright 2023, American Chemical Society. (g) Failure process of combined interlayer. (h) Failure stress model of combined interlayer. (i) Molecular structure of AIR. (j) The schematic diagram of synthetic route and crosslinking process of AIR. (k) Photographs of AIR and CAIR products. Reproduced with permission.¹³⁰ Copyright 2025, Wiley-VCH.

The common mechanistic underpinnings of functional layer failures can be attributed to stress concentration phenomena and subsequent defect proliferation. Both residual strains (e.g., thermally induced stresses) and externally applied strains (e.g., bending deformation) generate substantial shear stresses at layer interfaces, triggering crack initiation and delamination when these stresses exceed critical material strength thresholds. COMSOL multi physics simulations have elucidated how strain-induced structural perturbations increase perovskite layer resistance and modify electronic band structures, directly correlating mechanical deformation with deteriorated optoelectronic performance.¹²⁷ Implementing mechanically compliant interlayers, exemplified by acrylic isoprene rubber (AIR) with its exceptionally low Young's modulus (0.15 MPa) and high adhesion strength, has proven remarkably effective in suppressing interfacial delamination. Furthermore, pre-strain engineering strategies successfully release residual stresses, enabling devices to maintain 92.8% of their initial efficiency even after 50 000 bending cycles (Fig. 14h–k).¹³⁰ These findings collectively establish mechanical failure of functional layers as a critical determinant of F-PSC performance degradation, while demonstrating that judicious implementation of strain engineering, interface modification, and materials optimization strategies can substantially enhance device resilience under mechanical stress conditions.

3.2 Delamination failure

F-PSCs face significant challenges regarding mechanical stability, particularly delamination failure between functional layers under repeated bending or tensile stress, resulting in substantial device performance deterioration. Delamination failure refers to the loss of adhesion between the perovskite layer and adjacent functional layers, including ETLs, HTLs, or electrodes, leading to layer separation, crack propagation, and interfacial degradation. This failure mechanism originates from the complex interplay between intrinsic material properties, residual processing stresses, and applied mechanical loads. The following sections systematically analyze the specific mechanisms underlying delamination failure, including mechanical strain-induced interfacial degradation, defect proliferation with subsequent crack formation, and stress concentration arising from thermal expansion coefficient mismatches.

3.2.1 Mechanical strain-induced interfacial degradation. In F-PSCs, mechanical bending or stretching generates substantial interfacial strain between functional layers, primarily originating from elastic modulus disparities between substrates and active layers coupled with externally applied mechanical loads. When devices undergo bending deformation, stress concentrations develop at interfaces, particularly at the junction between the perovskite layer and conductive oxide electrodes (such as ITO), inducing lattice distortion and compromising adhesive strength. Interfacial strain and lattice distortion are unavoidable during the crystallization of perovskite thin films, leading to weak adhesion and eventual delamination under bending.³⁰ This strain-induced degradation extends beyond mechanical integrity compromise, triggering ion migration and interfacial defect generation that reduce carrier extraction efficiency and enhance non-radiative recombination pathways.

Quantitative analyses reveal that at critical bending radii (2–10 mm), von Mises stress distributions demonstrate maximum stress localization at ITO/perovskite interfaces, precisely correlating with observed delamination initiation sites.¹³³ Furthermore, strain-induced electronic band misalignment between perovskite and charge transport layers exacerbates interfacial recombination, manifesting as decreased V_oc and FF. Mechanical stress from bending and stretching leads to cracks and voids at grain boundaries, which act as pathways for moisture and oxygen ingress, exacerbating degradation.^116,134,135 This evidence demonstrates that mechanical strain not only directly precipitates delamination but also creates vulnerability to environmental degradation factors, accelerating chemical decomposition through multiple pathways.

3.2.2 Defect proliferation and crack formation. Delamination failure exhibits strong correlation with interfacial defect proliferation and crack propagation dynamics. Perovskite films inherently contain native point defects, particularly iodine vacancies and lead interstitials, that undergo migration and agglomeration under applied mechanical stress, forming microcracks and void structures. Residual tensile stress in perovskite materials can initiate a cascade of undesirable effects. At the atomic level, this stress can trigger displacement within the lattices, weakening the chemical bond integrity of the perovskite film.^136,137 This stress-induced defect proliferation diminishes material fracture toughness, rendering interfaces increasingly susceptible to fatigue failure under cyclic loading conditions.

In systematic bending tests, crack nucleation preferentially occurs at grain boundaries, which are regions characterized by elevated defect densities where strain energy concentrates, leading to progressive interfacial delamination and electrical performance deterioration. The grain boundary defects drastically quenched the photoluminescence intensity but became benign after air exposure (Fig. 15a and b).²⁹ This observation underscores that defect evolution impacts not only mechanical integrity but also compromises photoelectric conversion efficiency through enhanced non-radiative recombination pathways. Furthermore, crack formation disrupts the ohmic contact integrity between perovskite and transport layers, increasing series resistance and consequently reducing J_sc and overall power conversion efficiency. During repetitive bending cycles, crack propagation rates exhibit positive correlation with strain amplitude, ultimately culminating in catastrophic device failure.^133,139,140

Fig. 15 (a) Time resolved photoemission electron microscopy intensity reduction at different defect type locations in FA_0.78MA_0.17Cs_0.05Pb(I_0.83Br_0.17)₃ films; (b) PEEM images (left column) and work function maps (right columns) for selected defect clusters in FA_0.78MA_0.17Cs_0.05Pb(I_0.83Br_0.17)₃ films before and after dry air treatment upon illumination. Reproduced with permission.³¹ Copyright 2022, American Chemical Society. (c) Schematic illustration of the formation process of residual strained perovskite films (RS-PVK) crystallized on a substrate. The middle picture is the pre-applied compressive strain on a concave substrate (grid is indicated to show the strain on the substrate). Strain-free (SF-PVK) perovskite thin films crystallized on concavely curved substrates. Reproduced under the terms of the Creative Commons Attribution 4.0 International License (CC BY 4.0).¹³⁸ Copyright 2023, Copyright Liang et al. FEM simulation results of the von Mises stress distribution in the bent devices at a bending radius of (d) r = 10 mm, (e) r = 5 mm, and (f) r = 2 mm. Reproduced with permission.¹³³ Copyright 2022, American Chemical Society.

3.2.3 Thermal expansion mismatch-induced stress concentration. Thermal expansion coefficient (CTE) mismatch between adjacent functional layers constitutes another critical mechanism driving delamination failure, particularly during temperature fluctuations or thermal cycling processes. Perovskite materials typically exhibit relatively high thermal expansion coefficients compared to commonly employed substrates (such as PET and PEN) and electrode materials, which possess substantially lower CTEs. This fundamental mismatch generates significant residual thermal stresses during fabrication processes (particularly annealing) or operational temperature variations. The difference in thermal expansion coefficient between the perovskite layer and other adjacent layers is unavoidable, leading to tensile or compressive strain at the interface.¹⁴¹

During post-annealing cooling processes, perovskite layers undergo greater contraction than adjacent materials, generating tensile interfacial stresses that compromise adhesion strength and initiate delamination. Finite element simulations demonstrate that the von Mises stress of the ITO layer is the highest in the PET-ITO-based device, while the maximum stress occurs in the Ag layer in the PET-PH1000-based device (Fig. 15d–f).¹³³ These results indicate that while stress distribution profiles depend on specific material combinations, interface regions invariably experience stress concentration, promoting delamination processes. Additionally, thermal stress gradients accelerate ion migration phenomena, exemplified by iodine ions diffusing toward interfaces along stress gradients, creating high-defect concentration regions that further compromise mechanical stability. The induced stress in the perovskite layer due to thermal coefficient mismatch is as high as 50 MPa, which is enough to induce the deformation of some softer metals (Fig. 15c).^125,133 Such substantial stress magnitudes readily induce plastic deformation and interfacial failure, particularly under cyclic thermal loading conditions.

Interlayer delamination failure represents a fundamental mechanism underlying mechanical stability deterioration in flexible perovskite solar cells, originating primarily from mechanical strain-induced interfacial degradation, defect proliferation coupled with crack formation, and thermal expansion mismatch-induced stress concentration. These mechanisms operate synergistically, resulting in progressive adhesion deterioration, electrical performance degradation, and accelerated device lifetime reduction. Mechanical strain directly induces lattice distortion and interfacial separation, defect proliferation facilitates degradation through crack propagation and environmental penetration, while thermal expansion mismatches generate residual stresses during thermal cycling that further compromise interfacial integrity. Understanding these interconnected failure mechanisms provides crucial insights for developing next-generation flexible photovoltaic devices with enhanced mechanical durability and operational stability.

3.3 Environmental factors and mechanical coupling failure

F-PSCs simultaneously encounter mechanical stresses and environmental factors (moisture, oxygen, illumination) during practical application, creating complex degradation pathways through synergistic interactions. These coupled effects significantly accelerate performance deterioration beyond what would be observed from isolated stressors. Understanding these multi-factor degradation mechanisms is essential for developing high-performance flexible devices with extended operational lifetimes. This section systematically analyzes the synergistic interactions between mechanical deformation and various environmental factors that collectively compromise device stability.

3.3.1 Moisture-mechanical stress coupling failure. Moisture is widely recognized as a primary degradation catalyst for perovskite materials, while mechanical stress-induced microcracks and grain boundary damage create preferential pathways for moisture infiltration. This synergistic interaction substantially accelerates device performance deterioration through multiple degradation mechanisms.

Mechanistically, water molecules rapidly form hydrogen bonds with uncoordinated iodine atoms at perovskite surfaces, generating reversible intermediate hydrates (MAPbI₃·H₂O and MAPbI₃·2H₂O).^{25,26,142–144} This process progressively weakens the bonding between organic cations and the inorganic PbI₆ framework, ultimately resulting in perovskite decomposition into volatile hydroiodic acid (HI) and PbI₂, with complete loss of optoelectronic functionality (Fig. 16a).^145,146

Fig. 16 (a) The degradation process of organic–inorganic perovskites under high humidity. American Chemical Society.¹⁴⁸ Copyright 2023, Elsevier. (b) Structure and photograph of the F-PSCs. The moisture degradation and fragile nature for (c) the control perovskite and (d) the enhanced water resistance with flexural endurance due to cementation and passivation for the GBs. (d) Normalized PCE of F-PSCs measured under different bending radius after 1000 cycles. (e) Normalized PCE of F-PSCs measured under different bending radius after 1000 cycles. Reproduced with permission.¹⁴⁹ Copyright 2024, Wiley-VCH.

Mechanical stress from repetitive bending significantly exacerbates this degradation pathway. Grain boundaries, representing structural weak points within perovskite films, readily develop microcracks under mechanical loading, creating preferential channels for moisture infiltration. Chen et al. demonstrated an effective mitigation strategy by introducing sulfonated graphene oxide (s-GO) to form gel-like networks at grain boundaries, simultaneously passivating defects and creating water-resistant interfaces. Their s-GO-treated devices maintained 88% of initial efficiency after 1000 bending cycles at a 70° bending radius, substantially outperforming control devices (Fig. 16b–e).¹⁴⁷ This evidence confirms that enhancing grain boundary chemical stability and mechanical integrity effectively blocks moisture penetration pathways, improving environmental stability.

Beyond external moisture infiltration, the intrinsic hygroscopic nature of perovskite materials constitutes another critical factor driving mechanical property deterioration. Formamidinium (FA)-based perovskites (such as FAPbI₃) demonstrate particularly high moisture sensitivity, rapidly transforming from the photoactive black phase (α-FAPbI₃) to the photoinactive yellow phase (δ-FAPbI₃) in humid environments.^150,151 Theoretical calculations by Lin et al. revealed that water molecules form H₂O⋯H–N hydrogen bonds with FA⁺ cations while simultaneously establishing H₂O⋯I⁻ hydrogen bonds with iodide ions, inducing lattice volume contraction and reducing the phase transition energy barrier from 0.413 eV to minimal values, thereby accelerating the phase transformation process.¹⁵¹

For all-inorganic perovskites (such as CsPbI₃), moisture presence catalyzes black-to-yellow phase transitions even without apparent water infiltration. Dastidar et al. demonstrated that this phase transformation is driven by catalytic effects rather than equilibrium changes, as the phase transition enthalpy remains essentially constant.¹⁵² This indicates that microstructural alterations induced by mechanical stress may activate these catalytic effects and accelerate phase transitions even at relatively low humidity levels.

3.3.2 Oxygen-mechanical stress coupling failure. Oxygen represents another critical factor driving perovskite device degradation, with its coupling effects with mechanical stress frequently overlooked in stability analyses. Conventional lead-based perovskites exhibit relative stability toward oxygen under dark conditions; however, under illumination, the generation of iodine vacancies significantly accelerates oxygen diffusion (Fig. 17a).^27,28 These vacancies facilitate superoxide species (O²⁻) formation, which subsequently deprotonate organic cations (e.g., MA⁺), producing degradation products including water, methylamine, iodine, and lead iodide.^153,154

Fig. 17 (a) Schematic of the reaction steps of O₂ with CH₃NH₃PbI₃. Reproduced with permission.¹⁴⁸ Copyright 2023, Elsevier. (b) Structure of F-PSC with the enlarged structure for borax and interaction between borax and perovskite at GBs. Reproduced with permission.¹⁴⁹ Copyright 2022, Royal Society of Chemistry. (c) SEM images of the pristine AgNW and AgNW:MXene flexible electrodes. (d) Resistance changes of AgNW–PET, AgNW:Mxene-PET and ITO–PET at various curvature radius. (e) Normalized PCE of F-PSCs measured after 500 bending cycles within different curvature radius. Reproduced with permission.¹⁴⁹ Copyright 2022, Wiley-VCH.

Mechanical fatigue from repetitive bending amplifies oxygen-induced degradation. Microcracking in electrode materials and interfacial delamination between functional layers create additional pathways for oxygen penetration. Tin-based perovskites demonstrate particularly high oxygen sensitivity due to the substantially lower Sn²⁺/Sn⁴⁺ redox potential (+0.15 V) compared to Pb²⁺/Pb⁴⁺ (+1.67 V).¹⁵⁵ He et al. quantitatively demonstrated that even at extremely low oxygen concentrations (0.1 ppm), the Sn⁴⁺ proportion in FASnI₃ perovskites reaches 9.7%; increasing oxygen concentrations to 10 ppm and 100 ppm elevates Sn⁴⁺ proportions to 31.2% and 54.4%, respectively.¹⁵⁶ This oxidation phenomenon induces severe p-type doping and tin vacancy formation, substantially degrading device performance.

Transparent electrode materials commonly employed in flexible devices, including AgNWs and ITO, exhibit high susceptibility to oxidation and corrosion under mechanical stress. AgNWs networks develop microcracks and junction separation during bending, exposing silver surfaces that readily undergo oxidation and sulfidation when exposed to oxygen and moisture, significantly increasing electrode resistance.¹⁵⁷ Researchers have developed various protective strategies, including graphene-wrapped AgNWs¹⁴⁷ and MXene nanosheets as filling materials¹⁵⁸ (Fig. 17b and c). These approaches enhance both mechanical stability and oxidation resistance of electrodes, stabilizing performance metrics (Fig. 17d and e).

3.3.3 Light-mechanical stress coupling failure. Illumination and thermal stress exert complex influences on the mechanical stability of flexible perovskite devices. Illumination accelerates perovskite material degradation through photochemical and photothermal effects, while operational heat generates internal stresses between functional layers due to thermal expansion coefficient mismatches, which intensify during mechanical bending.

Under illumination, ion migration in perovskite materials is significantly enhanced, constituting a key factor driving performance degradation. Xing et al. demonstrated through polarization experiments that typical ion drift velocities in MAPbI₃ polycrystalline films reach 1.2 mm s⁻¹ under 1 sun illumination, substantially exceeding the 0.016 mm s⁻¹ observed under 0.02 sun conditions (Fig. 18a).¹⁵⁹ This enhanced ion migration stems from illumination-induced reduction in ion migration activation energy. Zhao et al. isolated ionic conductivity from electronic contributions through low-temperature conductivity measurements, revealing that illumination reduces activation energy from 0.82 eV to 0.15 eV, a five-fold decrease.¹⁶⁰ This enhanced ion migration induces phase separation and photo-induced degradation while exacerbating defect formation at grain boundaries under mechanical stress.

Fig. 18 (a) A local enlarged image of the filamentary paths across the covered MAPbI₃ film measured by a laser confocal scanning microscopy. Reproduced with permission.¹⁵⁹ Copyright 2016, Royal Society of Chemistry. (b) The stress levels of CsMAFA-triple cation (black) were measured at different temperatures and the comparison to the predicted stress levels. The stress levels of MAPbI₃ (red) were measured after formation at room temperature and with annealing at different temperatures, showing low-stress values in all cases. Reproduced under the terms of the Creative Commons Attribution 4.0 International License (CC BY 4.0).¹³¹ Copyright 2023, Copyright Li et al. (c) Architecture of the planar heterojunction n–i–p PSC using SDPs as the interfacial material. Scanning electron microscopy images of (d) the reference perovskite film and (e) the SDP-modified perovskite film. (f) TOF-SIMS mappings of the Cs signal of perovskite films without and with SDP modification after heating at 100 °C for 200 h. Above: reference, below: SDP-modified sample (g), (h) Long-term thermal stability of unencapsulated PSCs based on MAPbI₃, and (FA_0.95Cs_0.05)PbI₃ perovskite absorbers, respectively. (i) Long-term SPO tracking of nonencapsulated solar cells using white LED illumination. (j) The long-term stability tests of the PSCs stored in ambient air without encapsulation. Reproduced with permission.¹⁶⁵ Copyright 2021, American Chemical Society.

Further investigations attribute illumination-enhanced ion migration to increased halide vacancy concentrations. Photogenerated holes interact with iodide ions, producing iodine vacancies and neutral iodine atoms, which readily migrate to interstitial sites due to their smaller radii.^161,162 These iodine vacancies create channels for ion migration, enhancing ionic conductivity. In flexible devices, mechanical bending-induced stress further promotes vacancy migration and agglomeration, forming larger defect clusters that ultimately lead to performance deterioration.

Thermal stress represents another critical factor stemming from operational temperature increases and thermal expansion coefficient disparities between device layers. Perovskite materials exhibit exceptionally low thermal conductivity (approximately 0.4 W m⁻¹ K⁻¹), while commonly employed organic hole transport materials (e.g., Spiro-OMeTAD) demonstrate even lower values (approximately 0.15 W m⁻¹ K⁻¹), facilitating heat accumulation during device operation (Fig. 18f, upper image).^163,164 Zhou et al. effectively enhanced thermal transfer efficiency and stability by incorporating silica aerogel (SDP) into perovskite films as both a heat-dissipating medium and passivation agent (Fig. 18g–j).¹⁶⁵

Thermal expansion coefficient mismatches between flexible substrates and perovskite layers generate significant internal stresses during thermal cycling. Rolston et al. quantitatively demonstrated that residual stress in perovskite films exhibits linear correlation with annealing temperature, reaching tensile stress values of 57.6 ± 4.9 MPa at 100 °C annealing compared to 20.7 ± 6.6 MPa at 60 °C (Fig. 18b).¹⁶⁶ These thermal residual stresses superimpose with external stresses during mechanical bending, more readily reaching material fracture strength and inducing crack formation. The anticipated stress from thermal expansion (σ_ΔT) can be quantified using: σ_ΔT = E_p/(1 − ν_p) × (α_s − α_p) × ΔT, where E_p and ν_p represent perovskite Young's modulus and Poisson's ratio, α_s and α_p denote substrate and perovskite thermal expansion coefficients, and ΔT indicates temperature change.

Ultraviolet irradiation damage to flexible devices warrants particular attention, especially when TiO₂ serves as the electron transport layer. TiO₂ exhibits photocatalytic activity under UV illumination, accelerating perovskite degradation.^167–169 Leijtens et al. compared stability between devices with and without TiO₂, demonstrating that TiO₂-free devices maintained stable photocurrent after 1000 hours of continuous operation under full-spectrum simulated sunlight.¹⁷⁰ For flexible devices, UV irradiation additionally induces photodegradation of polymer substrates, further reducing mechanical strength and environmental barrier properties.

The synergistic coupling between environmental factors and mechanical stress constitutes a fundamental mechanism driving flexible perovskite solar cell performance degradation. Moisture infiltration through mechanically damaged regions induces perovskite decomposition and phase transitions; oxygen penetration accelerates electrode and functional layer oxidative degradation under mechanical fatigue; while illumination and thermal stress exacerbate mechanical failure through enhanced ion migration and internal stress generation. As illustrated in Table 2, these three mechanisms typically operate concurrently, mutually reinforcing each other to create complex coupled failure networks. Understanding these interactions provides critical insights for designing next-generation flexible perovskite devices with enhanced operational stability and mechanical durability under real-world conditions.

Table 2 Main failure mechanisms of environmental factors and mechanical stress coupling

Coupling factors	Failure mechanisms	Consequences
Moisture-mechanical stress	Moisture infiltration through microcracks and grain boundaries, inducing perovskite decomposition and phase transitions	Efficiency decline, complete device failure
Oxygen-mechanical stress	Oxygen penetration through electrode cracks, oxidizing sensitive layers and electrode materials	Resistance increase, enhanced charge recombination
Light-mechanical stress	Light-enhanced ion migration, thermal stress generating internal strain	Phase separation, crack formation, performance degradation

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4. Strategies for enhancing mechanical stability

4.1 Grain boundary patching

Polycrystalline perovskite films exhibit inherent mechanical heterogeneity, wherein grain boundaries possess substantially lower Young's modulus compared to grain interiors.^171,172 This discrepancy generates localized stress concentration under bending deformation, initiating crack formation and propagation that ultimately compromises device performance. To address this fundamental challenge, researchers have developed sophisticated grain boundarie patching strategies that systematically enhance mechanical homogeneity across the perovskite microstructure.

4.1.1 In situ formation of low dimensional perovskite phases. The formation of in situ low dimensional perovskite phases at GBs represents a promising approach to bridge modulus disparities between adjacent grains. Yan et al. developed post-treatment protocols utilizing 4-bromobenzylamine iodide (4-BBAI) that demonstrated particular efficacy, as 4-BBAI's low polarity enables selective reaction with residual PbI₂ at GBs during crystallization.¹⁷³ This strategic interaction generates continuous trans-GB structures that effectively harmonize the Young's modulus across GB regions and 3D perovskite grains. The resultant mechanical homogenization significantly enhances device durability, with F-PSCs retaining over 80% of their PCE after 8000 bending cycles at a radius of 4 mm. In a recent breakthrough, Tang et al. pioneered an innovative approach using phenylethylammonium-based 2D perovskite (PEA₂PbI₄) strategically incorporated at grain boundaries to function as molecular “lubricants” (Fig. 19a and b).³² The 2D PEA₂PbI₄ phases facilitate intergrain sliding and stress dissipation, fundamentally altering the material's response to mechanical deformation without compromising charge transport pathways within the 3D perovskite grains (Fig. 19e–h). When integrated within a comprehensive device architecture that included ultrathin substrates and optimized interfaces, this approach yielded exceptional mechanical resilience while achieving 21.44% power conversion efficiency (Fig. 19c). The devices maintained performance after 1000 bending cycles at an extremely small radius of 0.5 mm (Fig. 19d), demonstrating how strategic 2D/3D heterostructuring can simultaneously address both mechanical and electronic requirements in flexible photovoltaics.

Fig. 19 (a) and (b) SEM images of (a) a MAPbI₃ film and (b) a PEA₂PbI₄-added film after 1000-cyces bending. (c) J–V curves of an ultrathin f-PSC. (d) PCE evolution of a f-PSC under bending tests at 0.5 mm radius for 1000 cycles. (e) Raw and filtered (f) HRTEM image on the area close to the crack tip. (g) The shear strain mapping and (h) rotation angel mapping calculated from (f). Reproduced under the terms of the Creative Commons Attribution 4.0 International License (CC BY 4.0).¹⁷⁴ Copyright 2025, Copyright Tang et al.

Extending this paradigm beyond 2D phases, Yao et al. demonstrated the remarkable efficacy of 0D Cs₄Pb(IBr)₆ additives in all-inorganic CsPbI_2.81Br_0.19 perovskite films.⁸⁸ Unlike traditional approaches that primarily focus on modulus harmonization, this innovative strategy fundamentally transforms the mechanical response of the film by converting tensile stress to compressive stress, thereby inhibiting crack propagation under flexural strain. The mechanical resilience achieved through this stress-conversion mechanism is unprecedented, with devices maintaining over 97% of their initial efficiency after an extraordinary 60 000 bending cycles at a 5 mm radius. Furthermore, the 0D additives simultaneously enhanced crystallinity and passivated grain boundary defects, resulting in a high PCE of 14.25%. This dual enhancement of mechanical durability and photovoltaic performance highlights the promise of 0D additives for all-inorganic flexible perovskite photovoltaics, which traditionally face more significant mechanical challenges than their hybrid organic–inorganic counterparts.

Similar mechanical stabilization has been achieved using alternative molecular species such as BA₂PbI₄, (C₄H₉NH₃)₂PbI₄, and 4-guanidinobutanoic acid (GBA), each contributing to GB reinforcement through analogous mechanisms.^175–177 These diverse approaches collectively demonstrate that strategic incorporation of low-dimensional phases, including both 0D and 2D structures, offers versatile pathways to overcome the inherent mechanical limitations of perovskite photovoltaics while simultaneously enhancing their optoelectronic performance.

4.1.2 Molecular additives for defect passivation. Molecular additives that passivate defects at GBs represent another critical dimension of GB reinforcement. These specialized passivation agents target undercoordinated ions and vacancies prevalent at GBs, significantly improving mechanical resilience without compromising photovoltaic performance. For instance, artemisinin-modified devices retain 93.2% of their PCE even after 2000 bending cycles at a 10 mm radius.³⁴ Similarly, [6,6]-phenyl-C61-butyric oxetane dendron ester (C-PCBOD)-passivated MAPbI₃ maintains 96.7% of initial efficiency under considerable tensile strain.¹⁷⁸ Xie et al.'s work with molecular dipole engineering using fluorinated -CN additives showed how dual –CN groups coordinate with Pb²⁺ defects while fluorine atoms form hydrogen bonds with FA⁺ cations.¹⁷⁹ This mechanism effectively “stitches” GB defects and releases accumulated stress, with the optimally designed 2F-2CN additive enabling inverted F-PSCs to achieve 24.08% PCE while exhibiting exceptional mechanical reliability. Wang et al. developed a novel approach using multi-hydroxyl phenylacetic acids to mitigate mechanical-thermal mismatch in F-PSCs (Fig. 20a).¹⁸⁰ By systematically comparing molecules with one to three hydroxyl groups, they demonstrated these additives concentrate at grain boundaries where they form dual interactions-coordination bonds with Pb²⁺ and hydrogen bonds with perovskite components. This mechanism effectively reduces the perovskite's Young's modulus by 11.1% and thermal expansion coefficient by 38.5%, enhancing energy dissipation during deformation (Fig. 20b). The optimized inverted F-PSCs achieved impressive 25.01% PCE while maintaining 90% efficiency after 3000 bending cycles and 83% after 1000 hours at 85 °C (Fig. 20c and d).

Fig. 20 (a) The molecular structures and electrostatic potential (ESP) of PHPA, DHPA, and THPA, along with IGMH analysis visualizing the weak interactions between multi-hydroxyl molecules with –NH groups and I⁻ ions. (b) Temperature-dependent XRD characterization of the control and additive-modified perovskite films. (c) J–V characteristic curves of the control and additive-modified F-PSCs. (d) Thermal aging of unencapsulated devices in a nitrogen atmosphere at 85 ± 1 °C. (d) Mechanical stability under continuous bending with a fixed radius of 8 mm. Reproduced with permission.¹⁸⁰ Copyright 2025, John Wiley and Sons Ltd.

Yao et al. developed a “pre-bending passivation” strategy inspired by medical debridement for all-inorganic flexible perovskite solar cells.¹⁸¹ By subjecting CsPbI_2.81Br_0.19 films to controlled pre-bending (50 cycles, 3 mm radius) before 2-mercaptopyridine (2-MP) treatment, they created strategic microcracks enabling deeper penetration of the bifunctional passivation agent. DFT calculations confirmed strong coordination bonding (−1.82 eV) between 2-MP and undercoordinated Pb²⁺, effectively passivating defects while reducing the film's Young's modulus for more uniform stress distribution. The devices achieved 14.74% PCE with exceptional mechanical durability, maintaining 104% efficiency after 15 000 bending cycles (3 mm radius) and over 93% after 70 000 cycles (5 mm radius), demonstrating how strategic pre-treatment can significantly enhance mechanical resilience through improved passivation depth and effectiveness. The multifunctional nature of these additives simultaneously improves electronic performance while enhancing mechanical integrity by mitigating strain concentration at GBs and reducing the Young's modulus disparity between grains and boundaries.

The underlying mechanistic principle unifying these diverse approaches is the elimination of mechanical property gradients between grains and GBs. By strategically homogenizing stress distribution throughout the perovskite microstructure, these patching methodologies suppress crack nucleation and propagation, thereby substantially enhancing the bending endurance of flexible perovskite optoelectronic devices. This fundamental understanding provides a rational framework for the continued development of mechanically robust perovskite systems that maintain functional performance under increasingly demanding mechanical conditions.

4.2 Interface engineering

Interface engineering represents a critical strategy for addressing the inherent mechanical challenges in F-PSCs. The multi-layered architecture of these devices inherently creates vulnerable points where materials with disparate mechanical properties meet, resulting in stress concentration during bending operations.^182,183 These mechanical mismatches frequently manifest as interfacial delamination and crack propagation, ultimately compromising device performance and longevity.^36,184 Systematic approaches to interface design have emerged as effective solutions for enhancing mechanical resilience while maintaining photovoltaic performance.

4.2.1 Molecular-level interface engineering. Stress dissipation and adhesion reinforcement at critical interfaces constitute primary mechanisms for improving mechanical durability. The strategic incorporation of SAMs or polymer networks between functional layers significantly enhances interfacial toughness through the formation of hydrogen bonds or chemical bridges.^114,185,186

Recent advances in molecular design have further expanded interface engineering capabilities. Shi et al. pioneered systematic design of dual-site molecular dipole architectures through comprehensive screening of fluorine-terminated organic molecules that anchor to perovskite surfaces through robust Lewis acid–base interactions.¹⁵ These molecules not only improve energy level alignment and facilitate carrier extraction but have enabled devices achieving 25.47% efficiency with exceptional operational stability under 1000 hours of illumination. Similarly, Zhou et al. a soft conjugation extension strategy for SAMs has emerged as an effective approach to simultaneously address efficiency and mechanical durability challenges.³³ Their work focused on rationally designed [2-(9H-carbazol-9-yl)ethyl]phosphonic acid (2PACz) derivatives, particularly a molecule designated as PhT-2PACz, which exhibits exceptional self-assembly properties on ITO substrates (Fig. 21a and b). The rationally designed molecular modifier achieves exceptional self-assembly quality on ITO substrates through its soft conjugated segments that optimize intermolecular interactions while preserving conformational adaptability under mechanical deformation. F-PSCs utilizing this approach have achieved champion efficiencies of 24.75% while maintaining 97% of initial performance after 4000 multidirectional bending cycles at a 4 mm radius, demonstrating exceptional mechanical durability (Fig. 21d–f).

Fig. 21 (a) Molecular structure of 2PACz, T-2PACz, and PhT-2PACz. (b) The single crystal structure of the p scaffold of 2PACz exhibits the hard feature and weak intermolecular interactions. (c) The single crystal structure of the p-scaffold of PhT-2PACz exhibits the soft feature and strong intermolecular interactions. (d) A schematic of the F-PSCs developed in this study. (e) The champion J–V curves of F-PSCs using 2PACz or PhT-2PACz as HTLs. (f) The PCE evolution of F-PSCs with 2PACz or PhT-2PACz HTLs under multidirectional bending cycles. Reproduced with permission.¹⁸⁷ Copyright 2025, Royal Society of Chemistry.

Yi et al. implemented strategic dual-interface engineering using silane coupling agents at different interfaces within flexible perovskite solar cells.³⁵ Specifically, they employed TMPU to enhance SnO₂ conductivity and passivate SnO₂/perovskite interface defects, while simultaneously using TMFS with its trifluoromethyl (–CF₃) functional groups to treat the perovskite/spiro-OMeTAD interface. This complementary strategy exploiting the distinct chemical properties of different silane coupling agents significantly reduced interface defect density and non-radiative recombination losses. Consequently, the optimized F-PSCs achieved 20.06% PCE with excellent mechanical reliability and impressive environmental stability, maintaining 91.3% efficiency after 5000 bending cycles while retaining 86.1% of initial performance after 3000 hours of storage under ambient conditions.

4.2.2 Bridging interface approaches. Novel bridging interface approaches have demonstrated remarkable success in simultaneously addressing multiple challenges in flexible devices. Fahim et al. developed a cascade bridge interfacial design by transforming ZnO nanorods into ZIF-8 interface layers. This approach creates strong chemical bonds at critical interfaces, with nitrogen atoms in ZIF-8 forming bridges with Pb²⁺ in the perovskite, establishing a cascade energy structure that enhances electron transport while reducing interfacial recombination. The design eliminated detrimental OH⁻ groups on ZnO surfaces while forming beneficial Zn–N and Pb–N bonds. Performance improved significantly, with efficiency increasing from 15.08% to 17.10% and hysteresis dropping from >6% to <1%. The ZIF-8 interface enabled 91.7% efficiency retention after 720 hours in ambient conditions (versus 29.67% for control devices) and achieved 18.47% efficiency when applying 1.6% tensile strain. Additionally, the interface demonstrated excellent Pb²⁺ adsorption capacity, reducing lead leakage by 75% and addressing environmental concerns for commercial deployment (Fig. 22a).¹⁸⁸

Fig. 22 (a) Schematic illustration of the flexible PSC device with ZnO NRs and ZnO-ZIF-8 ETL. The degradation mechanism of perovskite at the ZnO/perovskite interface due to the presence of surface defects and OH⁻ groups on the ZnO surface (right side). The left-side image shows the advantages of the proposed strategy to avoid detrimental reactions by eliminating the surface defects of ZnO with the incorporation of ZIF-8 at ZnO/perovskite interface and its ability to adsorb toxic Pb²⁺ ion for minimizing the negative impact of Pb leaching on environmental sustainability. Reproduced under the terms of the Creative Commons Attribution 4.0 International License (CC BY 4.0).¹⁸⁸ Copyright 2025, Copyright Fahim et al. (b) Electrostatic potential (ESP) maps and dipole moments of 2-BBA, 3-BBA and 4-BBA. (c) PL and (d) TRPL spectra of perovskite films with introduction of 2-BBA, 3-BBA, and 4-BBA. (e) The architecture of inverted f-PSC. (f) J–V characteristics of the control f-PSC and the 4-BBA treated champion f-PSC. (g) Mechanical bending stability of control and 4-BBA-treated F-PSCs at a bending radius of 10 mm. Reproduced with permission.¹⁶ Copyright 2025, John Wiley and Sons Ltd.

Liang et al. introduced a multi-functionalized molecular design approach using 4-BBA as an additive in perovskite precursors (Fig. 22b).¹⁶ This innovative strategy enabled 4-BBA molecules to preferentially deposit at the critical interface between perovskite and substrate, creating stable hydrogen bond bridges through B–OH interactions with SAMs while simultaneously passivating Pb²⁺ defects through Lewis acid–base interactions (Fig. 22c and d). This comprehensive interfacial and defect engineering approach yielded impressive results with flexible perovskite solar cells achieving a record 25.30% efficiency (certified 25.13%) and an unprecedented 1.21 V open-circuit voltage (Fig. 22e). The devices also demonstrated superior mechanical durability, retaining 95.3% of initial performance after 5000 bending cycles at a 10 mm radius of curvature (Fig. 22f), highlighting how targeted molecular design can simultaneously address multiple challenges in flexible photovoltaic devices.

Extending these interfacial engineering concepts to more complex device architectures, Li et al. demonstrated flexible all-perovskite tandem solar cells approaching 25% efficiency by implementing molecule-bridged hole-selective contacts.¹¹⁴ Their approach utilized molecular bridging technology at critical interfaces to enhance adhesion between layers while simultaneously suppressing carrier recombination. This strategic interface modification not only improved charge extraction and device performance but also significantly enhanced the mechanical robustness of the tandem structure, showcasing how advanced interface engineering can enable both efficiency and flexibility in next-generation photovoltaics.

4.2.3 Multifunctional interface engineering. At the molecular level, defect passivation strategies further contribute to mechanical stabilization while simultaneously addressing electronic performance. Additives such as hydrogen-bonded polymers (HBPs) and bifunctional linkers, exemplified by trifluoroborate compounds, serve dual roles by passivating interfacial defects and strengthening adhesion between layers.

Li et al. developed a novel approach using polyamide-amine based HBPs to address multiple interface challenges simultaneously.¹⁸⁹ The synthesized HBPs featuring branched three-dimensional structure with abundant functional terminal groups form robust hydrogen bond networks at the SnO₂/perovskite interface, significantly enhancing interfacial adhesion and increasing fracture toughness from 1.08 to 2.13 J m⁻². This interfacial reinforcement enabled impressive photovoltaic performance, with HBP-modified devices achieving 25.05% PCE on rigid substrates and 23.86% on flexible substrates while maintaining 88.9% of initial efficiency after 10 000 bending cycles. Additionally, the abundant carboxyl and amino groups in HBPs effectively chelate Pb²⁺, providing 98% lead leakage inhibition efficiency-addressing a critical environmental concern for commercial deployment. The unique spherical shape and nanoscale internal cavities of HBPs facilitate energy absorption during deformation, while their low glass transition temperature maintains softness that accommodates thermal expansion mismatch between perovskite layers and substrates. Cao et al. proposed a passivation strategy using a bifunctional trifluorobenzoic acid as an additive to fabricate high-quality perovskite films.¹⁹⁰ The study indicated that the carboxyl group (–COOH) in the TFPA molecule could interact with lead ions and halogen vacancies in the perovskite, effectively reducing the defect density of the film and thereby enhancing the photoelectric conversion efficiency of perovskite solar cells; meanwhile, the fluorine-containing hydrophobic phenyl group in the molecule was oriented and arranged on the film surface, significantly enhancing the environmental stability of the device. In the continuous illumination test at the maximum power point, the device with TFPA addition maintained the initial efficiency of 93.22% after 10.5 hours, while the device without TFPA addition only degraded to the initial efficiency of 82.22% under the same conditions after 5 hours.

In a related study, researchers further developed this concept with a bioinspired hyperbranched dopamine polymer adhesive (HPDA) designed to enhance mechanical durability under high humidity conditions.¹⁹¹ Inspired by mussel adhesive proteins, HPDA features a hydrophobic backbone with hydrophilic dopamine side groups that provide strong underwater adhesion capability. The polymer preferentially distributes along perovskite grain boundaries and forms a three-dimensional mechanical reinforcement network throughout the film, with catechol groups forming bidentate hydrogen bonds with SnO₂ while aromatic structures generate π–π interactions with Spiro-OMeTAD. HPDA-modified flexible devices achieved impressive 24.43% efficiency while maintaining 94.1% of initial performance after 10 000 bending cycles at a 3 mm radius under humid conditions. Additionally, the polymer demonstrated 99% lead capture efficiency, significantly reducing environmental risks.

Cao et al. developed an innovative approach focusing on the buried interface between perovskite films and electron transport layers using phenylhydrazine chloride (PC) as an effective passivation agent. Strong interactions between PC and PbI₂ not only passivate interface defects but also delay perovskite crystallization, resulting in high-quality films with reduced defect density.¹⁹² This interface modification strategy achieved remarkable results, boosting efficiency from 24.67% to 25.80% in small-area devices and enabling flexible perovskite solar cells with impressive 24.54% efficiency. The modified devices also demonstrated exceptional stability, retaining 93.94% of initial performance after 1008 hours under ambient conditions (25 °C, 30% humidity), highlighting how targeted interface passivation can simultaneously enhance efficiency, stability, and mechanical robustness in flexible devices. Liu et al. employed ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate([BMIM]BF4) to modify SnO₂ electron transport layers in flexible devices, creating an interfacial dipolar layer that simultaneously facilitates charge transfer and passivates perovskite defects, boosting efficiency from 13.5% to 19.0% while maintaining compatibility with low-temperature processing (≤100 °C) required for flexible substrates.¹⁹³ Gao et al. implemented this strategy by modifying the perovskite/hole transport layer interface with PenAAc, where PenA⁺ and Ac⁻ ions form strong chemical bonds with acceptor and donor defects on the perovskite surface, resulting in certified record efficiency of 23.35% for flexible perovskite solar cells with exceptional mechanical durability, maintaining over 91% of initial efficiency after 5000 bending cycles.¹⁰⁸ Li et al. demonstrated this principle through a multifunctional trifluoroborate additive (PTFBK) (Fig. 23a) that not only passivates both anion and cation defects in perovskite materials, but also creates hydrogen bonds between FA and fluorine atoms, significantly reducing the Young's modulus and residual stress within the perovskite layer (Fig. 23c–h).¹⁹⁴ This comprehensive approach yielded impressive performance in both rigid and flexible inverted perovskite solar cells, achieving record efficiencies of 24.99% and 23.48% respectively, while providing exceptional mechanical resilience during bending tests (Fig. 23i and j). These modifications not only enhance charge extraction efficiency but also significantly reduce mechanical degradation mechanisms that typically compromise device longevity.

Fig. 23 (a) Chemical structure of PTFBK. (b) FAPbI₃ absorbing PTFBK and FAPbI₃-V_I absorbing PTFBK. GIXRD spectra at different depths of 200 and 500 nm of perovskite films, (c) and (f) control sample, and (d) and (g) target sample. Linear fit of 2θ–sin² ϕ of perovskite films at depths of (e) 200 and (h) 500 nm. (i) J–V characteristics from forward and reverse scans of the best flexible devices. (j) Mechanical test on a bending radius of 5 mm for flexible devices. Reproduced with permission.¹⁹⁴ Copyright 2024, John Wiley and Sons Ltd.

4.2.4 Scaling interface engineering for large-area modules. Translating interface engineering strategies from laboratory-scale cells to large-area modules represents a critical step toward commercialization. Recent advances have demonstrated significant progress in this direction. Zhu et al. addressed the critical challenge of interface delamination, which is particularly severe when scaling to larger areas.⁹³ Their innovative approach employed a bifacial linker benzyl(trifluoro)borate potassium (BnBF₃K) to significantly enhance adhesion at the SnO₂/perovskite interface. This molecular engineering strategy simultaneously improved electrical performance by reducing interfacial defects and optimizing energy level alignment. The result was a record-certified efficiency of 21.39% for flexible perovskite solar modules with substantial active areas of 12.80 cm², while single cells reached 24.15% efficiency. These modules demonstrated exceptional mechanical resilience, retaining 96.56% of initial performance after 6000 bending cycles. Dong et al. made significant advances in this direction by developing fully printed flexible perovskite solar mini-modules (f-PSMs) with substantial aperture areas of 20.25 cm².¹⁹⁵ By introducing a fullerene-substituted alkylphosphonic acid dipolar layer between roll-to-roll printed tin oxide electron transport layers and perovskite active layers (Fig. 24a and b), they effectively lowered energy barriers and suppressed interfacial recombination. These mini-modules achieved 11.6% aperture efficiency and maintained 90% of initial performance after 500 hours of damp heat testing (ISOS-D-3: 65 °C/85% relative humidity) when encapsulated (Fig. 24d and e). Xu et al. contributed to large-area module advancement by incorporating ultrathin acrylate polymer interlayers between the perovskite layer and hole transport layer (Fig. 24g and h).¹⁹⁶ This strategy employed varying organic chain lengths in monomer molecules to achieve a triple effect: chemical anchoring, physical water molecule barrier, and toughening network formation. Their approach yielded flexible modules (23.25 cm²) with impressive 20.78% efficiency under outdoor illumination conditions. The polymer-modified devices demonstrated exceptional humidity stability, maintaining over 85% of initial efficiency during humidity testing, and excellent bending durability with over 90% performance retention after bending tests. Notably, under indoor low-light conditions (6600 lx WLED), their modules achieved 40.1% efficiency, establishing a record for flexible perovskite photovoltaics (Fig. 24l). These collective advances in interface engineering demonstrate how strategic molecular design at critical interfaces can simultaneously address multiple stability challenges while enabling high-performance large-area flexible modules suitable for diverse application scenarios. Chu et al. proposed a printing strategy called EPM, aiming to address the issues of uneven crystallization and poor film quality in the printing process of flexible perovskite solar modules (FPSMs) due to the island effect and coffee ring effect.¹⁷ Through the relatively high peak shear rate provided by EPM, the shear force, Laplace force, and surface tension were regulated, which disrupted the island effect and weakened the coffee ring effect during the printing process. This was beneficial for the uniform distribution of perovskite colloid size, significantly regulating the perovskite crystallization kinetics, and thereby improving the crystallinity and uniformity of large-area perovskite films. The final F-PSC achieved a certified PCE of 25.44% on a 1.01 cm² area, setting a new record for current thin-film F-PSCs. Moreover, a FPSM device with an active area of 100 cm² was successfully prepared, with the certified PCE reaching up to 15.65%.

Fig. 24 (a) Chemical structures of monoFAPA and bisFAPA. (b) Schematic illustration of bisFAPA bonding to the SnO₂ surface. (c) Photograph of F-PSCs. (d) Representative J–V curves reference and FAPA-modified devices. (e) Normalized PCE of F-PSCs as a function of the number of mechanical bending cycles. (f) Damp-heat stability test for encapsulated f-PSMs in the best condition with bisFAPA modification. Reproduced under the terms of the Creative Commons Attribution 3.0 International License (CC BY 3.0).¹⁹⁵ Copyright 2024, Copyright Dong et al. (g) Chemical structure of triethylene glycol dimethacrylate (TEGDMA). (h) The possible interaction of the polymer with the perovskite lattice. (i) Normalized averaged PCE value for the F-PPVs as a function of bending cycles with a radius of 10 mm. (j) Application scenario diagram of future perovskite indoor PV device driving power devices. (k) WLED (6600 K) with 0.07 cm² active area and (l) WLED (6600 K) with 23.25 cm² active area. Reproduced with permission.¹⁹⁶ Copyright 2025, Elsevier.

4.3 Structural design innovations

Nature-evolved structural architectures offer sophisticated design principles that can address the fundamental mechanical challenges of F-PSCs. These biomimetic approaches can be strategically implemented at three hierarchical levels: microscopic material structure, interfacial design, and macroscopic device architecture. This multi-level biomimetic framework not only enhances mechanical resilience but often simultaneously improves photovoltaic performance.

4.3.1 Microscopic structure. The inherent brittleness of perovskite active layers represents a fundamental material limitation in F-PSCs, with conventional perovskite films exhibiting catastrophic failure under mechanical deformation. Biomimetic microstructural engineering directly addresses this intrinsic vulnerability by reconceptualizing the material's response to applied strain.

Nacre-inspired “brick-and-mortar” microstructures have emerged as a particularly effective strategy for enhancing mechanical flexibility while preserving the crystalline properties essential for photovoltaic performance. For instance, Hu et al. demonstrated that styrene–butadiene–styrene/polyurethane (SBS/PU) composites reduced Young's modulus from 260 MPa to 193 MPa, enabling large-area flexible devices (56.02 cm²) with sustained 7.91% PCE under mechanical stress.³⁷ Advancing this concept further, Zhao et al. implemented nano-WSe₂ as grain boundary lubricants (Fig. 25a), fundamentally altering the fracture behavior from intergranular to transgranular patterns (Fig. 25c and e). This microstructural modification yielded exceptional devices exceeding 25% PCE with 88.3% retention after 10 000 bending cycles (Fig. 25f–h).¹⁹⁷

Fig. 25 (a) Diagram of the nano-WSe₂ generated by the pulsed laser irradiation technology and the perovskite film embedded with WSe₂ nanocrystals. (b) Schematic illustration of the interaction between perovskite and nano-WSe₂. (c) Schematic illustration of stress distribution in the perovskite film before and after nano-WSe₂ embedding and fracture mechanism of the films during bending. SEM images of localized surface cracks in (d) control and (e) target perovskite films after bending tests. (f) J–V curves of 1.55 eV bandgap perovskite-based devices. (g) Light soaking stability test of the control and target PSCs performed under white LED lamp (100 mW cm⁻²). (h) Normalized PCE decay curves of the unencapsulated flexible device bending cycles with bending number, R = 3 mm. Reproduced with permission.¹⁹⁷ Copyright 2025, Wiley-VCH.

In addition to the “brick-mortar” microstructure, self-healing polymers have significantly enhanced the stability of flexible perovskite solar cells. Self-healing polymers not only prevent damaged areas but also enable flexible devices to have excellent electrical and mechanical properties by acting as scaffolds/repair agents.¹⁹⁸ Meng et al. proposed a strategy of combining polyurethane (S-PU) self-healing polymers with perovskite.¹⁹⁹ The S-PU self-healing polymer has dynamic covalent disulfide bonds and thermally reversible covalent bonds, demonstrating mechanical self-healing performance at 100 °C. Chen et al. designed a self-healing 5-(1,2-dithiolan-3-yl)pentanehydrazide hydroiodide (TA-NI) containing dynamic covalent disulfide bonds, hydrogen bonds, and ammonium.²⁰⁰ The study utilized the synchronous cross-linking property of the TA-NI molecule during perovskite film formation to form a ligament-like structure at the grain boundaries. This structure can effectively spontaneously repair defects induced by mechanical stress, thereby significantly enhancing the mechanical integrity of the film. The resulting flexible perovskite solar cells maintained over 90% performance in 20 000 bending cycles and 1248-hour operational stability tests. Han et al. synthesized two self-healing polymers, PU-MCU and PU-IU, with different cyclic bonds to control grain growth,²⁰¹ defect passivation mechanism, device stability, and mechanical energy distribution. Self-healing polymers not only improved perovskite film growth but also extended carrier lifetime. When the metal halide perovskite film was stretched, the film exhibited self-healing behavior by re-establishing hydrogen bonds after mechanical relaxation.

4.3.2 Interface and supporting structure. Delamination at layer interfaces and substrate cracking typically precede active layer failure in F-PSCs, often initiating device degradation under mechanical stress. Biomimetic modifications to supporting components and interfaces effectively counter these critical failure modes.

Substrate engineering has benefited substantially from natural material architectures. Ji et al. demonstrated that bamboo-derived cellulose nanofibril substrates offer exceptional tensile strength (230 MPa) with remarkable recovery after severe deformation.²⁰² Similarly, Jia et al. leveraged mica substrates with van der Waals-enabled interlayer slippage, achieving 91.7% efficiency retention after 5000 bending cycles.²⁰³ For transparent conductors, leaf venation-inspired electrode networks and biomimetic crack-templated metal grids have achieved an optimal balance between sheet resistance and optical transmittance, as demonstrated by Han et al.²⁰⁴

At critical interfaces, barnacle-inspired levodopa modifications have proven particularly effective in enhancing adhesion while simultaneously suppressing coffee-ring effects during solution processing, enabling highly uniform perovskite films with 21.08% efficiency. More remarkably, mussel-inspired hyperbranched dopamine polymers form robust chelation complexes with Pb²⁺, nearly doubling interfacial fracture energy from 1.12 to 2.14 J m⁻² and effectively mitigating delamination failures during mechanical deformation.²⁰⁵

4.3.3 Macroscopic architectures. Conventional planar device architectures fail to effectively distribute mechanical stress during flexing operations, while also struggling to simultaneously address multiple functional requirements. Biomimetic macroscopic architectures overcome these limitations through strategic structural configurations.

Vertebrate skeletal system-inspired designs employ alternating hard/soft layer arrangements to redistribute mechanical stress throughout the device stack. Meng et al. demonstrated that PEDOT:EVA composites could reduce PET/ITO substrate modulus by 46%, dramatically improving mechanical durability without compromising electrical performance.³⁶ For applications requiring extreme deformability, kirigami-based architectures have achieved extraordinary mechanical properties, including 200% stretchability and 450° twistability, through geometric patterning rather than relying solely on material properties.³⁸

Beyond mechanical resilience, multifunctional biomimetic designs effectively address several complementary requirements in F-PSCs. Glasswing butterfly-inspired anti-reflection films significantly increase light transmittance by 6.17%, elevating device PCEs to 22.72%, as shown by Siddique et al.²⁰⁶ Innovative peacock feather-inspired structural designs enable aesthetically distinctive bifacial devices with dual-side functionality,²⁰⁷ while corn bract-inspired protective coatings provide excellent hydrophobicity with a high 111.7° contact angle for moisture resistance (Fig. 26).²⁰⁸ Sophisticated springtail cuticle-inspired PDMS encapsulation layers offer comprehensive omnidirectional liquid repellency while substantially enhancing mechanical stability under repeated deformation.²⁰⁹ These diverse biological inspirations collectively advance the functional versatility and performance of next-generation flexible photovoltaic technologies.

Fig. 26 (a) The schematic representation of the “soft and hard” network of HNP coatings inspired by the structure of corn-leaf bract. (b) Photographs of water droplets on the surface of the HNP-3 on different substrates. (c) J–V curve of solar cells and photoelectric conversion efficiency (PCE) for glass, HNP-3 and HNP-3 after cleaning solar cells (insert picture). Reproduced with permission.²⁰⁸ Copyright 2025, Wiley-VCH.

These biomimetic approaches represent a promising frontier for creating mechanically robust, high-performance flexible solar technologies that could revolutionize portable power generation.

5. Conclusion and future perspectives

This review has systematically examined the mechanical stability of F-PSCs, highlighting significant advances in understanding and addressing this critical challenge for commercial deployment. Through comprehensive analysis of failure mechanisms and mitigation strategies, we have demonstrated how rational materials design and architectural innovation have substantially improved the mechanical resilience of these devices. Grain boundary engineering employing low-dimensional perovskite phases and molecular additives has effectively homogenized stress distribution and inhibited crack initiation, while interface engineering methodologies utilizing self-assembled monolayers, polymer networks, and bifunctional linkers have enhanced interfacial toughness between functional layers. Particularly promising are biomimetic structural designs inspired by natural systems such as nacre, vertebrate skeletons, and insect cuticles, which have provided innovative solutions for stress redistribution and damage tolerance. These convergent approaches have substantially advanced the mechanical resilience of F-PSCs, demonstrating the feasibility of achieving both exceptional photovoltaic performance and mechanical durability through rational materials design and architectural innovation.

Looking forward, several research directions appear particularly promising for developing mechanically robust F-PSCs suitable for commercial applications:

5.1 Multifunctional material systems

Future research should focus on developing materials that simultaneously address multiple stability challenges. The integration of low-dimensional perovskite phases has demonstrated significant potential in concurrently regulating stress distribution and passivating defects. Bioinspired hyperbranched polymers (e.g., HPDA, HBPs) that form three-dimensional adhesive networks through multiple hydrogen bonds and coordinative interactions represent another substantial advancement. Upcoming work should explore the strategic incorporation of dynamic bonds, hydrophobic moieties, and defect-passivating functional groups into unified molecular structures to address the complex mechanical stresses encountered in practical applications. These multifunctional materials must be designed to maintain optimal photovoltaic performance while enhancing mechanical resilience under diverse operational conditions. Specifically, for the lead leakage and toxicity issues of perovskite devices, priority should be given to developing multifunctional chemisorption materials with high lead chelating capacity, excellent mechanical compatibility, and retained photovoltaic performance, further expanding the application of low-dimensional composites and dynamic bonding systems in flexible devices.²¹⁰

5.2 Interfacial stress management and compatibility

The accumulation of stress at interfaces between different material components in F-PSCs presents substantial risks to mechanical integrity. These interfacial stresses frequently lead to delamination and crack propagation, compromising both mechanical stability and electrical performance. Interface engineering approaches employing gradient interfacial layers with tailored mechanical properties and optimized adhesion strengths are crucial for effective stress dissipation. Future research should delve deeper into the fundamental relationships between interfacial chemistry, mechanical behavior, and device longevity, enabling rational design of robust interfaces. Particular attention should be directed toward developing self-healing interfaces that can autonomously restore mechanical and electrical continuity after damage events.

5.3 Scalable manufacturing and process integration

As F-PSCs transition toward R2R production, a critical step for industrial scalability and commercialization, research must further develop scalable deposition techniques that ensure mechanical integrity over large areas.²¹¹ High-throughput processes such as slot-die coating and inkjet printing have emerged as critical pathways for large-scale manufacturing of flexible devices, yet require further optimization to meet commercial standards. Special attention should be directed toward the development and integration of stress-modulation processes that can be readily incorporated into existing manufacturing workflows. This includes optimizing solvent systems, controlling crystallization kinetics, and implementing in-line stress relief treatments to minimize residual stresses that precipitate mechanical failures during operation. Looking ahead, the convergence of intelligent process control and biomimetic structural designs could unlock new paradigms for high-throughput, defect-tolerant manufacturing, ultimately accelerating the commercialization of flexible perovskite photovoltaics.

5.4 Application-specific structural optimization

F-PSCs require tailored structural optimization for specific application scenarios. Wearable electronics demand devices capable of withstanding repeated bending and stretching, where bioinspired structural designs might provide optimal balance between stretchability and durability. Building-integrated photovoltaics require enhanced weather resistance and mechanical strength, while aerospace applications necessitate the ability to withstand extreme temperature variations and radiation environments. Future research should focus on developing application-specific device architectures that satisfy these diverse operational requirements without compromising photovoltaic performance. This targeted approach will accelerate the practical deployment of F-PSCs across multiple technological domains while addressing the unique mechanical challenges associated with each application environment.

5.5 Machine learning method

Machine learning (ML) has revolutionized perovskite optoelectronic research with successful applications in efficiency enhancement and autonomous material and device optimization.^212–214 These capabilities suggest that ML could play an equally influential role in addressing the persistent challenges of F-PSCs. F-PSCs are well-suited for wearable and portable electronic devices, yet they face inherent challenges including mechanical durability under repeated deformation, low-temperature processing constraints, and flexible electrode integration. ML might enable rapid exploration of material combinations on flexible substrates through high-throughput automated platforms, such as bend-resistant perovskite compositions and low-temperature-processable transport layers, and may also help optimize key processing parameters.

Author contributions

Conceptualization, J. Y., Z. L. and H. Z.; data curation, Z. L., H. Z. and Z. W.; formal analysis, J. Y., H. Z. and Z. W.; funding acquisition, J. Y., H. Z. and J. X.; investigation, Z. L., J. L. and H. Z.; methodology, Z. L., H. Z. and Z. W.; project administration, H. Z., J. L. and J. Y.; resources, H. Z., J. L. and P. Z.; software, S. L., X. H. and Y. W.; supervision, J. Y., H. Z. and Z. L.; validation, J. Y., H. Z. and J. L.; visualization, X. J., P. Z. and X. W.; writing – original draft, J. Y., H. Z. and Z.L.; writing – review & editing, Z. L., H. Z. and Z. W. All authors have read and agreed to the published version of the manuscript.

Conflicts of interest

The authors have no competing financial interests to declare.

Data availability

No primary research results, software or code have been included and no new data were generated or analyzed as part of this review.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (no. U22A20142), the Fundamental Research Funds for the Central Universities (2024JC007, 2025JG007), the Hebei Province High School Science Research Project (No. BJK2024155), the Innovative Research Group Project of Natural Science Foundation of Hebei Province (no. E2022209093), the Central Guiding Local Science and Technology Development Fund Project (254Z1005G, 246Z4309G). The Science and Technology Planning Project of Inner Mongolia Autonomous Region (2025YFHH0131).

References

1. J. Liu, T. Ye, D. Yu, S. Liu and D. J. A. C. I. E. Yang, Recoverable flexible perovskite solar cells for next-generation portable power sources, Angew. Chem., Int. Ed., 2023, 62(40), e202307225.
2. M. A. Green, E. D. Dunlop, M. Yoshita, N. Kopidakis, K. Bothe, G. Siefer, D. Hinken, M. Rauer, J. Hohl-Ebinger and X. J. Hao, Solar cell efficiency tables (Version 64), Prog. Photovolt. Res. Appl., 2024, 32(7), 425–441.
3. M. A. Green, A. Ho-Baillie and H. J. Snaith, The emergence of perovskite solar cells, Nat. Photonics, 2014, 8(7), 506–514.
4. T. Wu, Z. Qin, Y. Wang, Y. Wu, W. Chen, S. Zhang, M. Cai, S. Dai, J. Zhang and J. Liu, The main progress of perovskite solar cells in 2020–2021, Nano-Micro Lett., 2021, 13, 152.
5. J.-P. Correa-Baena, M. Saliba, T. Buonassisi, M. Grätzel, A. Abate, W. Tress and A. J. S. Hagfeldt, Promises and challenges of perovskite solar cells, Science, 2017, 358(6364), 739–744.
6. H. Dong, C. Ran, W. Gao, M. Li, Y. Xia and W. Huang, Metal Halide Perovskite for next-generation optoelectronics: progresses and prospects, ELight, 2023, 3(1), 3.
7. A. Kojima, K. Teshima, Y. Shirai and T. Miyasaka, Organometal halide perovskites as visible-light sensitizers for photovoltaic cells, J. Am. Chem. Soc., 2009, 131(17), 6050–6051.
8. H. Tan, A. Jain, O. Voznyy, X. Lan, F. P. García de Arquer, J. Z. Fan, R. Quintero-Bermudez, M. Yuan, B. Zhang and Y. J. S. Zhao, Efficient and stable solution-processed planar perovskite solar cells via contact passivation, Science, 2017, 355(6326), 722–726.
9. H. S. Jung, G. S. Han, N.-G. Park and M. J. J. J. Ko, Flexible perovskite solar cells, Joule, 2019, 3(8), 1850–1880.
10. L. Zhang, C. Fu, S. Wang, M. Wang, R. Wang, S. Xiang, Z. Wang, J. Liu, H. Ma and Y. J. A. F. M. Wang, Amorphous F-doped TiO_x Caulked SnO₂ electron transport layer for flexible perovskite solar cells with efficiency exceeding 22.5%, Adv. Funct. Mater., 2023, 33(11), 2213961.
11. Y. Wang, R. Lin, X. Wang, C. Liu, Y. Ahmed, Z. Huang, Z. Zhang, H. Li, M. Zhang and Y. J. N. C. Gao, Oxidation-resistant all-perovskite tandem solar cells in substrate configuration, Nat. Commun., 2023, 14(1), 1819.
12. G. Jeong, D. Koo, J. Seo, S. Jung, Y. Choi, J. Lee and H. J. N. L. Park, Suppressed interdiffusion and degradation in flexible and transparent metal electrode-based perovskite solar cells with a graphene interlayer, Nano Lett., 2020, 20(5), 3718–3727.
13. N. Ren, L. Tan, M. Li, J. Zhou, Y. Ye, B. Jiao, L. Ding and C. J. I. Yi, 25%-Efficiency flexible perovskite solar cells via controllable growth of SnO₂, iEnergy, 2024, 3(1), 39–45.
14. D. Gao, B. Li, Z. Li, X. Wu, S. Zhang, D. Zhao, X. Jiang, C. Zhang, Y. Wang and Z. J. A. M. Li, Highly efficient flexible perovskite solar cells through pentylammonium acetate modification with certified efficiency of 23.35%, Adv. Mater., 2023, 35(3), 2206387.
15. J. Shi, M. W. Samad, F. Li, C. Guo, C. Liu, J. Guo, Y. Zhang, J. Zeng, D. Wang and W. Ma, Dual-Site Molecular Dipole Enables Tunable Interfacial Field Toward Efficient and Stable Perovskite Solar Cells, Adv. Mater., 2024, 36(44), 2410464.
16. H. Liang, W. Zhu, Z. Lin, B. Du, H. Gu, T. Chen, F. Du, L. Bu, Y. Zhou and X. Xie, Enhancing Efficiency and Stability of Inverted Flexible Perovskite Solar Cells via Multi-Functionalized Molecular Design, Angew. Chem., Int. Ed., 2025, e202501267.
17. Z. Chu, B. Fan, W. Shi, Z. Xing, C. Gong, J. Li, L. Li, X. Meng, M. B. K. Niazi, X. Hu and Y. Chen, Synergistic Macroscopic–Microscopic Regulation: Dual Constraints of the Island Effect and Coffee-Ring Effect in Printing Efficient Flexible Perovskite Photovoltaics, Adv. Funct. Mater., 2025, 35(26), 2424191.
18. Z. Yuan, M. Yao, N. Zhang, S. Wang, X. Rui, Q. Zhang and Z. J. S. C. M. Niu, Mechanical analysis of flexible integrated energy storage devices under bending by the finite element method. Science China, Materials, 2021, 64(9), 2182–2192.
19. Q. Dong, M. Chen, Y. Liu, F. T. Eickemeyer, W. Zhao, Z. Dai, Y. Yin, C. Jiang, J. Feng and S. J. J. Jin, Flexible perovskite solar cells with simultaneously improved efficiency, operational stability, and mechanical reliability, Joule, 2021, 5(6), 1587–1601.
20. X. Leng, Y. Zheng, J. He, B. Shen, H. Wang, Q. Li, X. Liu, M. Lin, Y. Shi, Z. J. E. Wei and E. Science, Mechanical strengthening of a perovskite–substrate heterointerface for highly stable solar cells, Energy Environ. Sci., 2024, 17(12), 4295–4303.
21. N. Rolston, K. A. Bush, A. D. Printz, A. Gold-Parker, Y. Ding, M. F. Toney, M. D. McGehee and R. H. J. A. E. M. Dauskardt, Engineering stress in perovskite solar cells to improve stability, Adv. Energy Mater., 2018, 8(29), 1802139.
22. R. Cheacharoen, N. Rolston, D. Harwood, K. A. Bush, R. H. Dauskardt, M. D. J. E. McGehee and E. Science, Design and understanding of encapsulated perovskite solar cells to withstand temperature cycling, Energy Environ. Sci., 2018, 11(1), 144–150.
23. X. Meng, Z. Cai, Y. Zhang, X. Hu, Z. Xing, Z. Huang, Z. Huang, Y. Cui, T. Hu, M. Su, X. Liao, L. Zhang, F. Wang, Y. Song and Y. Chen, Bio-inspired vertebral design for scalable and flexible perovskite solar cells, Nat. Commun., 2020, 11(1), 3016.
24. J. Liu, T. Ye, D. Yu, S. Liu and D. Yang, Recoverable Flexible Perovskite Solar Cells for Next-Generation Portable Power Sources, Angew. Chem., Int. Ed., 2023, 62(40), e202307225.
25. J. Bisquert and E. J. Juarez-Perez, The causes of degradation of perovskite solar cells, ACS Publications, 2019, vol. 10, pp. 5889–5891.
26. G. Abdelmageed, L. Jewell, K. Hellier, L. Seymour, B. Luo, F. Bridges, J. Z. Zhang and S. Carter, Mechanisms for light induced degradation in MAPbI₃ perovskite thin films and solar cells, Appl. Phys. Lett., 2016, 109(23), 233905.
27. N. Aristidou, C. Eames, I. Sanchez-Molina, X. Bu, J. Kosco, M. S. Islam and S. A. Haque, Fast oxygen diffusion and iodide defects mediate oxygen-induced degradation of perovskite solar cells, Nat. Commun., 2017, 8(1), 15218.
28. J. M. Ball and A. Petrozza, Defects in perovskite-halides and their effects in solar cells, Nat. Energy, 2016, 1(11), 1–13.
29. S. Kosar, A. J. Winchester, T. A. Doherty, S. Macpherson, C. E. Petoukhoff, K. Frohna, M. Anaya, N. S. Chan, J. Madéo and M. K. Man, Unraveling the varied nature and roles of defects in hybrid halide perovskites with time-resolved photoemission electron microscopy, Energy Environ. Sci., 2021, 14(12), 6320–6328.
30. Y. Chen, Y. Lei, Y. Li, Y. Yu, J. Cai, M.-H. Chiu, R. Rao, Y. Gu, C. Wang and W. Choi, Strain engineering and epitaxial stabilization of halide perovskites, Nature, 2020, 577(7789), 209–215.
31. B. P. Finkenauer, X. Akriti, K. Ma and L. Dou, Degradation and self-healing in perovskite solar cells, ACS Appl. Mater. Interfaces, 2022, 14(21), 24073–24088.
32. G. Tang, F. Zheng, J. Song, Q. Tai, J. Zhao and F. Yan, Holistic Optimization toward Ultrathin Flexible Perovskite Solar Cells with High Efficiency and Mechanical Robustness, Adv. Sci., 2025, 12(27), 2415372.
33. B. Zhou, M. Li, Q. Xiong, L. Zhang, S. Zhang, J. Sun, J. Tang and W. C. Choy, Soft conjugation extension strategy of self-assembled molecules for achieving efficient and mechanically stable flexible perovskite solar cells, Energy Environ. Sci., 2025, 18, 8803–8814.
34. L. Yang, Q. Xiong, Y. Li, P. Gao, B. Xu, H. Lin, X. Li and T. Miyasaka, Artemisinin-passivated mixed-cation perovskite films for durable flexible perovskite solar cells with over 21% efficiency, J. Mater. Chem. A, 2021, 9(3), 1574–1582.
35. Z. Yi, X. Li, B. Xiao, Q. Jiang, Y. Luo and J. Yang, Dual-interface engineering induced by silane coupling agents with different functional groups constructing high-performance flexible perovskite solar cells, Chem. Eng. J., 2023, 469, 143790.
36. X. Meng, Z. Cai, Y. Zhang, X. Hu, Z. Xing, Z. Huang, Z. Huang, Y. Cui, T. Hu and M. Su, Bio-inspired vertebral design for scalable and flexible perovskite solar cells, Nat. Commun., 2020, 11(1), 3016.
37. X. Hu, Z. Huang, F. Li, M. Su, Z. Huang, Z. Zhao, Z. Cai, X. Yang, X. Meng and P. Li, Nacre-inspired crystallization and elastic “brick-and-mortar” structure for a wearable perovskite solar module, Energy Environ. Sci., 2019, 12(3), 979–987.
38. J. Qi, H. Xiong, C. Hou, Q. Zhang, Y. Li and H. Wang, A kirigami-inspired island-chain design for wearable moistureproof perovskite solar cells with high stretchability and performance stability, Nanoscale, 2020, 12(6), 3646–3656.
39. D. Lv, Q. Jiang, Y. Shang and D. Liu, Highly efficient fiber-shaped organic solar cells toward wearable flexible electronics, npj Flexible Electron., 2022, 6(1), 38.
40. Z. Du, J. Wen, T. Li, X. Wang, H. Zhang and Y. Chen, Nature-Inspired Structure Design for Robust and Efficient Flexible Perovskite Solar Cells, Small, 2025, e08389.
41. H. S. Jung, G. S. Han, N.-G. Park and M. J. Ko, Flexible Perovskite Solar Cells, Joule, 2019, 3(8), 1850–1880.
42. H. Liu, H. Han, J. Xu, X. Pan, K. Zhao, S. Liu and J. Yao, A 0D Additive for Flexible All-Inorganic Perovskite Solar Cells to Go Beyond 60 000 Flexible Cycles, Adv. Mater., 2023, 35(28), 2300302.
43. X. Li, H. Yu, Z. Liu, J. Huang, X. Ma, Y. Liu, Q. Sun, L. Dai, S. Ahmad, Y. Shen and M. Wang, Progress and Challenges Toward Effective Flexible Perovskite Solar Cells, Nano-Micro Lett., 2023, 15(1), 206.
44. S. Guo, J. Yi, Y. Sun and H. Zhou, Recent advances in titanium-based electrode materials for stationary sodium-ion batteries, Energy Environ. Sci., 2016, 9(10), 2978–3006.
45. J. Yu, M. Wang and S. Lin, Probing the Soft and Nanoductile Mechanical Nature of Single and Polycrystalline Organic–Inorganic Hybrid Perovskites for Flexible Functional Devices, ACS Nano, 2016, 10(12), 11044–11057.
46. Y. Du, H. Cai, X. Bao, Z. Xing, Y. Wu, J. Xu, L. Huang, J. Ni, J. Li and J. Zhang, Flexible Perovskite Solar Cells onto Plastic Substrate Exceeding 13% Efficiency Owing to the Optimization of CH₃NH₃PbI_3–xCl_x Film via H₂O Additive, ACS Sustainable Chem. Eng., 2018, 6(1), 1083–1090.
47. R. Tian, S. Zhou, Y. Meng, C. Liu and Z. Ge, Material and Device Design of Flexible Perovskite Solar Cells for Next-Generation Power Supplies, Adv. Mater., 2024, 36(37), 2311473.
48. H. Yang, H.-C. Kwon, S. Ma, K. Kim, S.-C. Yun, G. Jang, J. Park, H. Lee, S. Goh and J. Moon, Energy Level-Graded Al-Doped ZnO Protection Layers for Copper Nanowire-Based Window Electrodes for Efficient Flexible Perovskite Solar Cells, ACS Appl. Mater. Interfaces, 2020, 12(12), 13824–13835.
49. L. Zhang, H. Ma, Z. Ying, Q. Dong, M. Yuan, S. Rong, Z. Wang, S. Wang, S. Li, J. Zhang, D. Cao, W. Han, Y. Yan, W. Tian, J. Bian and Y. Shi, Lowering Charge Transport Barriers by Eliminating the Electric Double Layer Residues to Reconstruct Adjacent SnO₂ Nanocrystals for High-Efficiency Flexible Perovskite Solar Cells, Adv. Funct. Mater., 2024, 34(45), 2406946.
50. T. Luo, G. Ye, X. Chen, H. Wu, W. Zhang and H. Chang, F-doping-Enhanced Carrier Transport in the SnO₂/Perovskite Interface for High-Performance Perovskite Solar Cells, ACS Appl. Mater. Interfaces, 2022, 14(37), 42093–42101.
51. J. Fan, Y. Yang, T. Jiang, J. Zhang, L. Wu, W. Wang, G. Zeng, J. Li, M. A. Halim and X. Hao, Performance Enhancement of Flexible Perovskite Solar Cells Enabled by Ammonium Halide Passivation, Energy Fuels, 2023, 37(23), 19220–19229.
52. D. A. M. de Alencar, G. Koch, F. De Rossi, A. Generosi, G. Ferraro, M. Bonomo, S. Noola, G. Pellis, P. Quagliotto, B. Paci, F. Brunetti and C. Barolo, Phenothiazine-Modified PTAA Hole Transporting Materials for Flexible Perovskite Solar Cells: A Trade-Off Between Performance and Sustainability, Adv. Sustainable Syst., 2025, 9(1), 2400674.
53. T. Li, Y. Zhu, Z. Du, J. Wen, Y. Xie, L. Huan, M. Duan, H. Zhang and Y. Chen, Rational Interface Design Toward Mechanically Durable Flexible Perovskite Solar Cells, Small, 2025, 21(26), 2503109.
54. X. Hu, X. Meng, L. Zhang, Y. Zhang, Z. Cai, Z. Huang, M. Su, Y. Wang, M. Li, F. Li, X. Yao, F. Wang, W. Ma, Y. Chen and Y. Song, A Mechanically Robust Conducting Polymer Network Electrode for Efficient Flexible Perovskite Solar Cells, Joule, 2019, 3(9), 2205–2218.
55. X. Yang, H. Yang, M. Su, J. Zhao, X. Meng, X. Hu, T. Xue, Z. Huang, Y. Lu, Y. Li and Z. Yang, Scalable Flexible Perovskite Solar Cells Based on a Crystalline and Printable Template with Intelligent Temperature Sensitivity, Sol. RRL, 2022, 6(4), 2100991.
56. Y. Zhu, Y. Zhang, M. Hu, Y. Hao, W. Huang, H. Park and J. Lu, Slot-Die Coating Ultra-Uniform NiOx Hole Transporting Layer via Eliminating the “Coffee-Ring” Effect for Flexible Perovskite Solar Modules, Adv. Funct. Mater., 2025, e12921.
57. A. A. Goje, N. A. Ludin, M. A. Ibrahim, S. Sepeai, M. S. Su'ait, U. Syafiq and P. Chelvanathan, Optimization of PCBM electron transport layer concentration for the fabrication of lead-free flexible perovskite solar cells, J. Renewable Sustainable Energy, 2025, 17(4), 043505.
58. S. Wu, J. Zhang, M. Qin, F. Li, X. Deng, X. Lu, W.-J. Li and A. K. Y. Jen, Manipulating Crystallographic Orientation via Cross-Linkable Ligand for Efficient and Stable Perovskite Solar Cells, Small, 2023, 19(19), 2207189.
59. Y. Zhu, Y. Zhang, M. Hu, Y. Hao, W. Huang, H. Park and J. Lu, Slot-Die Coating Ultra-Uniform NiOx Hole Transporting Layer via Eliminating the “Coffee-Ring” Effect for Flexible Perovskite Solar Modules, Adv. Funct. Mater., 2025, e12921.
60. M. Dkhili, G. Lucarelli, F. De Rossi, B. Taheri, K. Hammedi, H. Ezzaouia, F. Brunetti and T. M. Brown, Attributes of High-Performance Electron Transport Layers for Perovskite Solar Cells on Flexible PET versus on Glass, ACS Appl. Energy Mater., 2022, 5(4), 4096–4107.
61. J. M. Burst, W. L. Rance, D. M. Meysing, C. A. Wolden, W. K. Metzger, S. M. Garner, P. Cimo, T. M. Barnes, T. A. Gessert and M. O. Reese In Performance of transparent conductors on flexible glass and plastic substrates for thin film photovoltaics, 2014, pp. 1589-1592.
62. M. Lee, Y. Jo, D. S. Kim and Y. Jun, Flexible organo-metal halide perovskite solar cells on a Ti metal substrate, J. Mater. Chem. A, 2015, 3(8), 4129–4133.
63. M. Lee, Y. Ko, B. K. Min and Y. Jun, Silver Nanowire Top Electrodes in Flexible Perovskite Solar Cells using Titanium Metal as Substrate, ChemSusChem, 2016, 9(1), 31–35.
64. J. P. Tiwari, Flexible Perovskite Solar Cells: A Futuristic IoTs Powering Solar Cell Technology, Short Review, Small Methods, 2025, 9(1), 2400624.
65. L. Gao, L. Chao, M. Hou, J. Liang, Y. Chen, H.-D. Yu and W. Huang, Flexible, transparent nanocellulose paper-based perovskite solar cells, npj Flexible Electron., 2019, 3(1), 4.
66. K. Zhu, Z. Lu, S. Cong, G. Cheng, P. Ma, Y. Lou, J. Ding, N. Yuan, M. H. Rümmeli and G. Zou, Ultraflexible and Lightweight Bamboo-Derived Transparent Electrodes for Perovskite Solar Cells, Small, 2019, 15(33), 1902878.
67. H. Wang, X. Zhang, Y. Ma, M. Wang and J. Wang, Giant Humidity Effect of 2D Perovskite on Paper Substrate: Optoelectronic Performance and Mechanical Flexibility, Adv. Opt. Mater., 2023, 11(12), 2203016.
68. Z. Xu, T. Xue, Q. Guo, J. Yao, G. Li, J. Du, E. Zhou and Z. Tan, Emerging flexible photovoltaic technology: From materials to devices, Inform. Funct. Mater., 2025, 2(1), 1–39.
69. B. T. Feleki, R. K. M. Bouwer, M. M. Wienk and R. A. J. Janssen, Perovskite Solar Cells on Polymer-Coated Smooth and Rough Steel Substrates, Sol. RRL, 2022, 6(4), 2100898.
70. U. Ryu, S. Jee, J.-S. Park, I. K. Han, J. H. Lee, M. Park and K. M. Choi, Nanocrystalline Titanium Metal–Organic Frameworks for Highly Efficient and Flexible Perovskite Solar Cells, ACS Nano, 2018, 12(5), 4968–4975.
71. B. Cao, L. Yang, S. Jiang, H. Lin, N. Wang and X. Li, Flexible quintuple cation perovskite solar cells with high efficiency, J. Mater. Chem. A, 2019, 7(9), 4960–4970.
72. A. Madeira, D. T. Papanastasiou, T. Toupance, L. Servant, M. Tréguer-Delapierre, D. Bellet and I. A. Goldthorpe, Rapid synthesis of ultra-long silver nanowires for high performance transparent electrodes, Nanoscale Adv., 2020, 2(9), 3804–3808.
73. D. Bellet, M. Lagrange, T. Sannicolo, S. Aghazadehchors, V. H. Nguyen, D. P. Langley, D. Muñoz-Rojas, C. Jiménez, Y. Bréchet and N. D. Nguyen, Transparent Electrodes Based on Silver Nanowire Networks: From Physical Considerations towards Device Integration, Materials, 2017, 570.
74. W. Chen, R. Zhang, X. Yang, H. Wang, H. Yang, X. Hu and S. Zhang, A 1D:2D structured AgNW:MXene composite transparent electrode with high mechanical robustness for flexible photovoltaics, J. Mater. Chem. C, 2022, 10(22), 8625–8633.
75. J. H. Heo, D. H. Shin, M. H. Jang, M. L. Lee, M. G. Kang and S. H. Im, Highly flexible, high-performance perovskite solar cells with adhesion promoted AuCl₃-doped graphene electrodes, J. Mater. Chem. A, 2017, 5(40), 21146–21152.
76. H. Dong, Z. Wu, Y. Jiang, W. Liu, X. Li, B. Jiao, W. Abbas and X. Hou, A flexible and thin graphene/silver nanowires/polymer hybrid transparent electrode for optoelectronic devices, ACS Appl. Mater. Interfaces, 2016, 8(45), 31212–31221.
77. D. Koo, S. Jung, J. Seo, G. Jeong, Y. Choi, J. Lee, S. M. Lee, Y. Cho, M. Jeong and J. Lee, Flexible organic solar cells over 15% efficiency with polyimide-integrated graphene electrodes, Joule, 2020, 4(5), 1021–1034.
78. Y. Li, R. Wen, P. Li and X. Fan, Metallic and low-work-function PEDOT: PSS cathodes for flexible organic solar cells exhibiting over 15% efficiency and high stability, ACS Appl. Energy Mater., 2022, 5(6), 7692–7700.
79. S. I. Na, S. S. Kim, J. Jo and D. Y. Kim, Efficient and flexible ITO-free organic solar cells using highly conductive polymer anodes, Adv. Mater., 2008, 20(21), 4061–4067.
80. X. Fan, B. Xu, S. Liu, C. Cui, J. Wang and F. Yan, Transfer-printed PEDOT: PSS electrodes using mild acids for high conductivity and improved stability with application to flexible organic solar cells, ACS Appl. Mater. Interfaces, 2016, 8(22), 14029–14036.
81. H. Luo, X. Lin, X. Hou, L. Pan, S. Huang and X. Chen, Efficient and air-stable planar perovskite solar cells formed on graphene-oxide-modified PEDOT: PSS hole transport layer, Nano-Micro Lett., 2017, 9(4), 39.
82. W. Cao, J. Li, H. Chen and J. Xue, Transparent electrodes for organic optoelectronic devices: a review, J. Photonics Energy, 2014, 4(1), 040990.
83. X. Wang, A. K. K. Kyaw, C. Yin, F. Wang, Q. Zhu, T. Tang, P. I. Yee and J. Xu, Enhancement of thermoelectric performance of PEDOT: PSS films by post-treatment with a superacid, RSC Adv., 2018, 8(33), 18334–18340.
84. Y. Li, L. Meng, Y. Yang, G. Xu, Z. Hong, Q. Chen, J. You, G. Li, Y. Yang and Y. Li, High-efficiency robust perovskite solar cells on ultrathin flexible substrates, Nat. Commun., 2016, 7(1), 10214.
85. G. Hashmi, K. Miettunen, T. Peltola, J. Halme, I. Asghar, K. Aitola, M. Toivola and P. Lund, Review of materials and manufacturing options for large area flexible dye solar cells, Renewable Sustainable Energy Rev., 2011, 15(8), 3717–3732.
86. Z. Song, C. Li, L. Chen and Y. Yan, Perovskite solar cells go bifacial—mutual benefits for efficiency and durability, Adv. Mater., 2022, 34(4), 2106805.
87. C. Ran, Y. Wang, W. Gao, Y. Xia, Y. Chen and W. Huang, Lead Sources in Perovskite Solar Cells: Toward Controllable, Sustainable, and Large-Scalable Production, Sol. RRL, 2021, 5(12), 2100665.
88. H. Liu, H. Han, J. Xu, X. Pan, K. Zhao, S. Liu and J. Yao, A 0D Additive for Flexible All-Inorganic Perovskite Solar Cells to Go Beyond 60 000 Flexible Cycles, Adv. Mater., 2023, 35(28), 2300302.
89. Z. Yang, C. C. Chueh, F. Zuo, J. H. Kim, P. W. Liang and A. K. Y. Jen, High-performance fully printable perovskite solar cells via blade-coating technique under the ambient condition, Adv. Energy Mater., 2015, 5(13), 1500328.
90. T. Ahmad, B. Wilk, E. Radicchi, R. Fuentes Pineda, P. Spinelli, J. Herterich, L. A. Castriotta, S. Dasgupta, E. Mosconi and F. De Angelis, New fullerene derivative as an n-type material for highly efficient, flexible perovskite solar cells of ap–i–n configuration, Adv. Funct. Mater., 2020, 30(45), 2004357.
91. P. Holzhey, M. Prettl, S. Collavini, C. Mortan and M. Saliba, Understanding the impact of surface roughness: changing from FTO to ITO to PEN/ITO for flexible perovskite solar cells, Sci. Rep., 2023, 13(1), 6375.
92. W. Qiu, U. W. Paetzold, R. Gehlhaar, V. Smirnov, H.-G. Boyen, J. G. Tait, B. Conings, W. Zhang, C. B. Nielsen and I. McCulloch, An electron beam evaporated TiO₂ layer for high efficiency planar perovskite solar cells on flexible polyethylene terephthalate substrates, J. Mater. Chem. A, 2015, 3(45), 22824–22829.
93. X. Zhu, Y. Li, Q. Z. Li, N. Wang, S. Yang, X. Gao, L. Zhang, P. Wang, Z. Liang and J. Li, Restrictive Heterointerfacial Delamination in Flexible Perovskite Photovoltaics Using a Bifacial Linker, Adv. Mater., 2025, 37(13), 2419329.
94. J. Wu, X. Xu, Y. Zhao, J. Shi, Y. Xu, Y. Luo, D. Li, H. Wu and Q. Meng, DMF as an Additive in a Two-Step Spin-Coating Method for 20% Conversion Efficiency in Perovskite Solar Cells, ACS Appl. Mater. Interfaces, 2017, 9(32), 26937–26947.
95. M. Xu, J. Feng, Z.-J. Fan, X.-L. Ou, Z.-Y. Zhang, H.-Y. Wang and H.-B. Sun, Flexible perovskite solar cells with ultrathin Au anode and vapour-deposited perovskite film, Sol. Energy Mater. Sol. Cells, 2017, 169, 8–12.
96. N. Jiang, H.-W. Zhang, Y.-F. Liu, Y.-F. Wang, D. Yin and J. Feng, Transfer-imprinting-assisted growth of 2D/3D perovskite heterojunction for efficient and stable flexible inverted perovskite solar cells, Nano Lett., 2023, 23(13), 6116–6123.
97. O. Y. Gong, G. S. Han, S. Lee, M. K. Seo, C. Sohn, G. W. Yoon, J. Jang, J. M. Lee, J. H. Choi and D.-K. Lee, van der Waals force-assisted heat-transfer engineering for overcoming limited efficiency of flexible perovskite solar cells, ACS Energy Lett., 2022, 7(9), 2893–2903.
98. M. Haghighi, N. Ghazyani, S. Mahmoodpour, R. Keshtmand, A. Ghaffari, H. Luo, R. Mohammadpour, N. Taghavinia and M. Abdi-Jalebi, Low-Temperature Processing Methods for Tin Oxide as Electron Transporting Layer in Scalable Perovskite Solar Cells, Sol. RRL, 2023, 7(10), 2201080.
99. Z. Yi, X. Li, B. Xiao, Y. Luo, Q. Jiang and J. Yang, Large improvement of photovoltaic performance of flexible perovskite solar cells using a multifunctional phospho-ethanolamine-modified SnO2 layer. Science China, Materials, 2022, 65(12), 3392–3401.
100. L. Zhang, H. Ma, Z. Ying, Q. Dong, M. Yuan, S. Rong, Z. Wang, S. Wang, S. Li and J. Zhang, Lowering Charge Transport Barriers by Eliminating the Electric Double Layer Residues to Reconstruct Adjacent SnO2 Nanocrystals for High-Efficiency Flexible Perovskite Solar Cells, Adv. Funct. Mater., 2024, 34(45), 2406946.
101. L. Yang, J. Feng, Z. Liu, Y. Duan, S. Zhan, S. Yang, K. He, Y. Li, Y. Zhou and N. Yuan, Record-efficiency flexible perovskite solar cells enabled by multifunctional organic ions interface passivation, Adv. Mater., 2022, 34(24), 2201681.
102. Z. Wu, P. Li, J. Zhao, T. Xiao, H. Hu, P. Sun, Z. Wu, J. Hao, C. Sun and H. Zhang, Low-Temperature-Deposited TiO₂ Nanopillars for Efficient and Flexible Perovskite Solar Cells, Adv. Mater. Interfaces, 2021, 8(3), 2001512.
103. W. Xu, X. Tang, J. Xiong, W. Xu, H. Zhou, C. Yu, Y. Lou and L. Feng, Organic-Hydrochloride-Modified ZnO Electron Transport Layer for Efficient Defect Passivation and Stress Release in Rigid and Flexible all Inorganic Perovskite Solar Cells, Small, 2024, 20(32), 2312230.
104. M. J. Peers, D. H. Thornton, Y. N. Majchrzak, G. Bastille-Rousseau and D. L. Murray, De-extinction potential under climate change: extensive mismatch between historic and future habitat suitability for three candidate birds, Biol. Conserv., 2016, 197, 164–170.
105. L. Huang, Z. Hu, J. Xu, K. Zhang, J. Zhang, J. Zhang and Y. Zhu, Efficient and stable planar perovskite solar cells with a non-hygroscopic small molecule oxidant doped hole transport layer, Electrochim. Acta, 2016, 196, 328–336.
106. Y. Wang, L. Duan, M. Zhang, Z. Hameiri, X. Liu, Y. Bai and X. Hao, PTAA as efficient hole transport materials in perovskite solar cells: a review, Sol. RRL, 2022, 6(8), 2200234.
107. Y. Li, J.-F. Liao, H. Pan and G. Xing, Interfacial Engineering for High-Performance PTAA-Based Inverted 3D Perovskite Solar Cells, Sol. RRL, 2022, 6(12), 2200647.
108. D. Gao, B. Li, Z. Li, X. Wu, S. Zhang, D. Zhao, X. Jiang, C. Zhang, Y. Wang and Z. Li, Highly efficient flexible perovskite solar cells through pentylammonium acetate modification with certified efficiency of 23.35%, Adv. Mater., 2023, 35(3), 2206387.
109. X. Ma, W. Peng, S. Jiang, M. Li, A. Zhang, C. Li and X. Li, How to stabilize the current of efficient inverted flexible perovskite solar cells at the maximum power point, Small, 2024, 20(26), 2310568.
110. D. Wang, Z. Liu, Y. Qiao, Z. Jiang, P. Zhu, J. Zeng, W. Peng, Q. Lian, G. Qu and Y. Xu, Rigid molecules anchoring on NiOx enable> 26% efficiency perovskite solar cells, Joule, 2025, 9(3), 101815.
111. J. Xie, Q. Chen, Q. Xue, I. F. Perepichka and G. Xie, H₂O₂-modified NiOx for perovskite photovoltaic modules, Innovation, 2024, 5(4), 100650.
112. Q. Lian, P. l Wang, G. Wang, X. Zhang, Y. Huang, D. Li, G. Mi, R. Shi, A. Amini and L. Zhang, Doping free and amorphous NiOx film via UV irradiation for efficient inverted perovskite solar cells, Adv. Sci., 2022, 9(18), 2201543.
113. J. Suo, B. Yang, D. Bogachuk, G. Boschloo and A. Hagfeldt, The dual use of SAM molecules for efficient and stable perovskite solar cells, Adv. Energy Mater., 2025, 15(2), 2400205.
114. L. Li, Y. Wang, X. Wang, R. Lin, X. Luo, Z. Liu, K. Zhou, S. Xiong, Q. Bao and G. Chen, Flexible all-perovskite tandem solar cells approaching 25% efficiency with molecule-bridged hole-selective contact, Nat. Energy, 2022, 7(8), 708–717.
115. Y. Xu, F. Fei, X. Dong, L. Li, Y. Li, N. Yuan and J. Ding, Uniform Coverage Functional Layers Enable High-Efficient Flexible Perovskite Solar Modules with an Outstanding Fill Factor, Sol. RRL, 2023, 7(16), 2300283.
116. Z. Zheng, F. Li, J. Gong, Y. Ma, J. Gu, X. Liu, S. Chen and M. Liu, Pre-buried additive for cross-layer modification in flexible perovskite solar cells with efficiency exceeding 22%, Adv. Mater., 2022, 34(21), 2109879.
117. Y. Yu, M. T. Hoang, Y. Yang and H. Wang, Critical assessment of carbon pastes for carbon electrode-based perovskite solar cells, Carbon, 2023, 205, 270–293.
118. T. M. Schmidt, T. T. Larsen-Olsen, J. E. Carlé, D. Angmo and F. C. Krebs, Upscaling of perovskite solar cells: fully ambient roll processing of flexible perovskite solar cells with printed back electrodes, Adv. Energy Mater., 2015, 5(15), 1500569.
119. B. A. Kamino, B. Paviet-Salomon, S.-J. Moon, N. Badel, J. Levrat, G. Christmann, A. Walter, A. Faes, L. Ding and J. J. Diaz Leon, Low-temperature screen-printed metallization for the scale-up of two-terminal perovskite–silicon tandems, ACS Appl. Energy Mater., 2019, 2(5), 3815–3821.
120. V. Ferguson, S. R. P. Silva and W. Zhang, Carbon materials in perovskite solar cells: prospects and future challenges, Energy Environ. Mater., 2019, 2(2), 107–118.
121. U. Kim, J. S. Nam, J. Yoon, J. Han, M. Choi and I. Jeon, Enhanced performance of solution-processed carbon nanotube transparent electrodes in foldable perovskite solar cells through vertical separation of binders by using eco-friendly parylene substrate, Carbon Energy, 2024, 6(7), e471.
122. F. Deng, Y. Shen, Y. Li, X. Han, M. Huang and X. Tao, Highly Efficient (>13%) and Robust Flexible Perovskite Solar Cells Using an Ultrasimple All-Carbon-Electrode Configuration, ACS Appl. Mater. Interfaces, 2023, 15(39), 46054–46063.
123. X. Yao, J. Duan, Y. Zhao, J. Zhang, Q. Guo, Q. Zhang, X. Yang, Y. Duan, P. Yang and Q. Tang, Stretchable alkenamides terminated Ti₃C₂T_x MXenes to release strain for lattice-stable mixed-halide perovskite solar cells with suppressed halide segregation, Carbon Energy, 2023, 5(12), e387.
124. X. Wu, G. Xu, F. Yang, W. Chen, H. Yang, Y. Shen, Y. Wu, H. Chen, J. Xi, X. Tang, Q. Cheng, Y. Chen, X.-M. Ou, Y. Li and Y. Li, Realizing 23.9% Flexible Perovskite Solar Cells via Alleviating the Residual Strain Induced by Delayed Heat Transfer, ACS Energy Lett., 2023, 8(9), 3750–3759.
125. S. He, S. Li, A. Zhang, G. Xie, X. Wang, J. Fang, Y. Qi and L. Qiu, Residual strain reduction leads to efficiency and operational stability improvements in flexible perovskite solar cells, Mater. Adv., 2022, 3(15), 6316–6323.
126. Z. Xu, R. Yu, T. Xue, Q. Guo, Q. Lv, C. Zhang, E. Zhou and Z. Tan, Stress release via thermodynamic regulation towards efficient flexible perovskite solar cells, Energy Environ. Sci., 2025, 18, 4324–4334.
127. M. Zhang, Y. Qiang, Z. Li, Z. Li and C. Zhang, Mechanism and regulation of tensile-induced degradation of flexible perovskite solar cells, Energy Adv., 2024, 3(6), 1431–1438.
128. Q. Li, Y. Zheng, H. Wang, X. Liu, M. Lin, X. Sui, X. Leng, D. Liu, Z. Wei, M. Song, D. Li, H. G. Yang, S. Yang and Y. Hou, Graphene-polymer reinforcement of perovskite lattices for durable solar cells, Science, 2025, 387(6738), 1069–1077.
129. J.-I. Park, J. H. Heo, S.-H. Park, K. I. Hong, H. G. Jeong, S. H. Im and H.-K. Kim, Highly flexible InSnO electrodes on thin colourless polyimide substrate for high-performance flexible CH₃NH₃PbI₃ perovskite solar cells, J. Power Sources, 2017, 341, 340–347.
130. T. Zhang, X. Pan, J. Li, X. Tang, G. Xu, X. Lin, C. Han, W. Liu, T. Xu, S. Huang, H. Mou, Y. Yin, J. Zheng, C. Ju, J. Zhu and Y. Li, Exclusive Encapsulation Adhesive in a Neutral-Plane Model for Ultrahigh Mechanical Stability of Flexible Perovskite Solar Cells, Adv. Mater., 2025, 37(34), 2501776.
131. X. Li, H. Yu, Z. Liu, J. Huang, X. Ma, Y. Liu, Q. Sun, L. Dai, S. Ahmad, Y. Shen and M. Wang, Progress and Challenges Toward Effective Flexible Perovskite Solar Cells, Nano-Micro Lett., 2023, 15(1), 206.
132. T. W. Jones, A. Osherov, M. Alsari, M. Sponseller, B. C. Duck, Y.-K. Jung, C. Settens, F. Niroui, R. Brenes and C. V. Stan, Lattice strain causes non-radiative losses in halide perovskites, Energy Environ. Sci., 2019, 12(2), 596–606.
133. H. Xie, T. Liang, X. Yin, J. Liu, D. Liu, G. Wang, B. Gao and W. Que, Mechanical stability study on PEDOT: PSS-based ITO-free flexible perovskite solar cells, ACS Appl. Energy Mater., 2022, 5(3), 3081–3091.
134. Y. Meng, C. Liu, R. Cao, J. Zhang, L. Xie, M. Yang, L. Xie, Y. Wang, X. Yin and C. Liu, Pre-buried ETL with bottom-up strategy toward flexible perovskite solar cells with efficiency over 23%, Adv. Funct. Mater., 2023, 33(28), 2214788.
135. Z. Wang, J. Wang, Z. Li, Z. Chen, L. Shangguan, S. Fan and Y. Duan, Crosslinking and densification by plasma-enhanced molecular layer deposition for hermetic seal of flexible perovskite solar cells, Nano Energy, 2023, 109, 108232.
136. X. Li, H. Yu, Z. Liu, J. Huang, X. Ma, Y. Liu, Q. Sun, L. Dai, S. Ahmad and Y. Shen, Progress and challenges toward effective flexible perovskite solar cells, Nano-Micro Lett., 2023, 15(1), 206.
137. M. F. Kanninen, An augmented double cantilever beam model for studying crack propagation and arrest, Int. J. Fract., 1973, 9(1), 83–92.
138. H. Liang, W. Yang, J. Xia, H. Gu, X. Meng, G. Yang, Y. Fu, B. Wang, H. Cai and Y. Chen, Strain effects on flexible perovskite solar cells, Adv. Sci., 2023, 10(35), 2304733.
139. O. V. Oyelade, O. Oyewole, D. Oyewole, S. Adeniji, R. Ichwani, D. Sanni and W. Soboyejo, Pressure-assisted fabrication of perovskite solar cells, Sci. Rep., 2020, 10(1), 7183.
140. J. Luo, J. Xia, H. Yang, C. Sun, N. Li, H. A. Malik, H. Shu, Z. Wan, H. Zhang and C. J. Brabec, A pressure process for efficient and stable perovskite solar cells, Nano Energy, 2020, 77, 105063.
141. D.-J. Xue, Y. Hou, S.-C. Liu, M. Wei, B. Chen, Z. Huang, Z. Li, B. Sun, A. H. Proppe and Y. Dong, Regulating strain in perovskite thin films through charge-transport layers, Nat. Commun., 2020, 11(1), 1514.
142. J. I. J. Choi, M. E. Khan, Z. Hawash, K. J. Kim, H. Lee, L. K. Ono, Y. Qi, Y.-H. Kim and J. Y. Park, Atomic-scale view of stability and degradation of single-crystal MAPbBr₃ surfaces, J. Mater. Chem. A, 2019, 7(36), 20760–20766.
143. G. Mannino, I. Deretzis, E. Smecca, F. Giannazzo, S. Valastro, G. Fisicaro, A. La Magna, D. Ceratti and A. Alberti, CsPbBr₃, MAPbBr₃, and FAPbBr₃ bromide perovskite single crystals: interband critical points under dry N₂ and optical degradation under humid air, J. Phys. Chem. C, 2021, 125(9), 4938–4945.
144. R. Long, W. Fang and O. V. Prezhdo, Moderate humidity delays electron–hole recombination in hybrid organic–inorganic perovskites: time-domain ab initio simulations rationalize experiments, J. Phys. Chem. Lett., 2016, 7(16), 3215–3222.
145. E. Mosconi, J. M. Azpiroz and F. De Angelis, Ab initio molecular dynamics simulations of methylammonium lead iodide perovskite degradation by water, Chem. Mater., 2015, 27(13), 4885–4892.
146. J. M. Frost, K. T. Butler, F. Brivio, C. H. Hendon, M. Van Schilfgaarde and A. Walsh, Atomistic origins of high-performance in hybrid halide perovskite solar cells, Nano Lett., 2014, 14(5), 2584–2590.
147. C. H. Chen, Z. H. Su, Y. H. Lou, Y. J. Yu, K. L. Wang, G. L. Liu, Y. R. Shi, J. Chen, J. J. Cao and L. Zhang, Full-dimensional grain boundary stress release for flexible perovskite indoor photovoltaics, Adv. Mater., 2022, 34(16), 2200320.
148. Q.-Q. Chu, Z. Sun, D. Wang, B. Cheng, H. Wang, C.-P. Wong and B. Fang, Encapsulation: The path to commercialization of stable perovskite solar cells, Matter, 2023, 6(11), 3838–3863.
149. F. Song, D. Zheng, J. Feng, J. Liu, T. Ye, Z. Li, K. Wang, S. Liu and D. Yang, Mechanical durability and flexibility in perovskite photovoltaics: advancements and applications, Adv. Mater., 2024, 36(18), 2312041.
150. G. E. Eperon, S. D. Stranks, C. Menelaou, M. B. Johnston, L. M. Herz and H. J. Snaith, Formamidinium lead trihalide: a broadly tunable perovskite for efficient planar heterojunction solar cells, Energy Environ. Sci., 2014, 7(3), 982–988.
151. D. Lin, Y. Gao, T. Zhang, Z. Zhan, N. Pang, Z. Wu, K. Chen, T. Shi, Z. Pan and P. Liu, Vapor deposited pure α-FAPbI3 perovskite solar cell via moisture-induced phase transition strategy, Adv. Funct. Mater., 2022, 32(48), 2208392.
152. S. Dastidar, C. J. Hawley, A. D. Dillon, A. D. Gutierrez-Perez, J. E. Spanier and A. T. Fafarman, Quantitative phase-change thermodynamics and metastability of perovskite-phase cesium lead iodide, J. Phys. Chem. Lett., 2017, 8(6), 1278–1282.
153. N. Aristidou, I. Sanchez-Molina, T. Chotchuangchutchaval, M. Brown, L. Martinez, T. Rath and S. A. Haque, The role of oxygen in the degradation of methylammonium lead trihalide perovskite photoactive layers, Angew. Chem., 2015, 127(28), 8326–8330.
154. F. T. O'Mahony, Y. H. Lee, C. Jellett, S. Dmitrov, D. T. Bryant, J. R. Durrant, B. C. O'Regan, M. Graetzel, M. K. Nazeeruddin and S. A. Haque, Improved environmental stability of organic lead trihalide perovskite-based photoactive-layers in the presence of mesoporous TiO₂, J. Mater. Chem. A, 2015, 3(14), 7219–7223.
155. N. K. Noel, S. D. Stranks, A. Abate, C. Wehrenfennig, S. Guarnera, A.-A. Haghighirad, A. Sadhanala, G. E. Eperon, S. K. Pathak and M. B. Johnston, Lead-free organic–inorganic tin halide perovskites for photovoltaic applications, Energy Environ. Sci., 2014, 7(9), 3061–3068.
156. X. He, T. Wu, X. Liu, Y. Wang, X. Meng, J. Wu, T. Noda, X. Yang, Y. Moritomo and H. Segawa, Highly efficient tin perovskite solar cells achieved in a wide oxygen concentration range, J. Mater. Chem. A, 2020, 8(5), 2760–2768.
157. J. J. Patil, W. H. Chae, A. Trebach, K. J. Carter, E. Lee, T. Sannicolo and J. C. Grossman, Failing forward: Stability of transparent electrodes based on metal nanowire networks, Adv. Mater., 2021, 33(5), 2004356.
158. W. Chen, R. Zhang, X. Yang, H. Wang, H. Yang, X. Hu and S. Zhang, A 1D: 2D structured AgNW: MXene composite transparent electrode with high mechanical robustness for flexible photovoltaics, J. Mater. Chem. C, 2022, 10(22), 8625–8633.
159. J. Xing, Q. Wang, Q. Dong, Y. Yuan, Y. Fang and J. Huang, Ultrafast ion migration in hybrid perovskite polycrystalline thin films under light and suppression in single crystals, Phys. Chem. Chem. Phys., 2016, 18(44), 30484–30490.
160. Y.-C. Zhao, W.-K. Zhou, X. Zhou, K.-H. Liu, D.-P. Yu and Q. Zhao, Quantification of light-enhanced ionic transport in lead iodide perovskite thin films and its solar cell applications, Light: Sci. Appl., 2017, 6(5), e16243.
161. G. Y. Kim, A. Senocrate, T.-Y. Yang, G. Gregori, M. Grätzel and J. Maier, Large tunable photoeffect on ion conduction in halide perovskites and implications for photodecomposition, Nat. Mater., 2018, 17(5), 445–449.
162. D. Barboni and R. A. De Souza, The thermodynamics and kinetics of iodine vacancies in the hybrid perovskite methylammonium lead iodide, Energy Environ. Sci., 2018, 11(11), 3266–3274.
163. R. Heiderhoff, T. Haeger, N. Pourdavoud, T. Hu, M. Al-Khafaji, A. Mayer, Y. Chen, H.-C. Scheer and T. Riedl, Thermal conductivity of methylammonium lead halide perovskite single crystals and thin films: a comparative study, J. Phys. Chem. C, 2017, 121(51), 28306–28311.
164. Z. Guo, S. J. Yoon, J. S. Manser, P. V. Kamat and T. Luo, Structural phase-and degradation-dependent thermal conductivity of CH3NH3PbI3 perovskite thin films, J. Phys. Chem. C, 2016, 120(12), 6394–6401.
165. F. Pei, N. Li, Y. Chen, X. Niu, Y. Zhang, Z. Guo, Z. Huang, H. Zai, G. Liu and Y. Zhang, Thermal management enables more efficient and stable perovskite solar cells, ACS Energy Lett., 2021, 6(9), 3029–3036.
166. N. Rolston, K. A. Bush, A. D. Printz, A. Gold-Parker, Y. Ding, M. F. Toney, M. D. McGehee and R. H. Dauskardt, Engineering stress in perovskite solar cells to improve stability, Adv. Energy Mater., 2018, 8(29), 1802139.
167. Z. Ni, H. Jiao, C. Fei, H. Gu, S. Xu, Z. Yu, G. Yang, Y. Deng, Q. Jiang and Y. Liu, Evolution of defects during the degradation of metal halide perovskite solar cells under reverse bias and illumination, Nat. Energy, 2022, 7(1), 65–73.
168. Y. Jiang, S.-C. Yang, Q. Jeangros, S. Pisoni, T. Moser, S. Buecheler, A. N. Tiwari and F. Fu, Mitigation of vacuum and illumination-induced degradation in perovskite solar cells by structure engineering, Joule, 2020, 4(5), 1087–1103.
169. J. Kim, A. Ho-Baillie and S. Huang, Review of novel passivation techniques for efficient and stable perovskite solar cells, Sol. RRL, 2019, 3(4), 1800302.
170. T. Leijtens, G. E. Eperon, S. Pathak, A. Abate, M. M. Lee and H. J. Snaith, Overcoming ultraviolet light instability of sensitized TiO₂ with meso-superstructured organometal tri-halide perovskite solar cells, Nat. Commun., 2013, 4(1), 2885.
171. A. F. Castro-Méndez, J. Hidalgo and J. P. Correa-Baena, The role of grain boundaries in perovskite solar cells, Adv. Energy Mater., 2019, 9(38), 1901489.
172. I. Visoly-Fisher, S. R. Cohen, K. Gartsman, A. Ruzin and D. Cahen, Understanding the beneficial role of grain boundaries in polycrystalline solar cells from single-grain-boundary scanning probe microscopy, Adv. Funct. Mater., 2006, 16(5), 649–660.
173. Y. Yan, R. Wang, Q. Dong, Y. Yin, L. Zhang, Z. Su, C. Wang, J. Feng, M. Wang and J. Liu, Polarity and moisture induced trans-grain-boundaries 2D/3D coupling structure for flexible perovskite solar cells with high mechanical reliability and efficiency, Energy Environ. Sci., 2022, 15(12), 5168–5180.
174. G. Tang, F. Zheng, J. Song, Q. Tai, J. Zhao and F. Yan, Holistic Optimization toward Ultrathin Flexible Perovskite Solar Cells with High Efficiency and Mechanical Robustness, Adv. Sci., 2025, 2415372.
175. B. Liu, M. Long, M. Cai, L. Ding and J. Yang, Interfacial charge behavior modulation in 2D/3D perovskite heterostructure for potential high-performance solar cells, Nano Energy, 2019, 59, 715–720.
176. Y.-W. Jang, S. Lee, K. M. Yeom, K. Jeong, K. Choi, M. Choi and J. H. Noh, Intact 2D/3D halide junction perovskite solar cells via solid-phase in-plane growth, Nat. Energy, 2021, 6(1), 63–71.
177. Z. Wang, Y. Lu, Z. Xu, J. Hu, Y. Chen, C. Zhang, Y. Wang, F. Guo and Y. Mai, An embedding 2D/3D heterostructure enables high-performance FA-alloyed flexible perovskite solar cells with efficiency over 20%, Adv. Sci., 2021, 8(22), 2101856.
178. M. Li, Y. G. Yang, Z. K. Wang, T. Kang, Q. Wang, S. H. Turren-Cruz, X. Y. Gao, C. S. Hsu, L. S. Liao and A. Abate, Perovskite grains embraced in a soft fullerene network make highly efficient flexible solar cells with superior mechanical stability, Adv. Mater., 2019, 31(25), 1901519.
179. L. Xie, S. Du, J. Li, C. Liu, Z. Pu, X. Tong, J. Liu, Y. Wang, Y. Meng and M. Yang, Molecular dipole engineering-assisted strain release for mechanically robust flexible perovskite solar cells, Energy Environ. Sci., 2023, 16(11), 5423–5433.
180. Y. Wang, W. Chang, W. You, H. Xue, Y. Zhou and J. Zhou, Constructing Synergistic Interactions Between Multi-Hydroxyl Molecules and Perovskite to Alleviate Mechanical-Thermal Mismatch for Achieving High-Performance Flexible Solar Cells, Angew. Chem., 2025, e202512376.
181. H. Liu, J. Xu, H. Han, C. Zhao, Y. Fu, K. Lang, P. Zou, X. Pan, X. Gao and K. Zhao, Debridement Strategy by Pre-Bending Passivation for Flexible All-Inorganic Perovskite Solar Cells Beyond 70 000 Bending Cycles, Adv. Funct. Mater., 2024, 34(34), 2400975.
182. Z. Dai, S. K. Yadavalli, M. Chen, A. Abbaspourtamijani, Y. Qi and N. P. Padture, Interfacial toughening with self-assembled monolayers enhances perovskite solar cell reliability, Science, 2021, 372(6542), 618–622.
183. B. L. Watson, N. Rolston, K. A. Bush, T. Leijtens, M. D. McGehee and R. H. Dauskardt, Cross-linkable, solvent-resistant fullerene contacts for robust and efficient perovskite solar cells with increased J sc and V oc, ACS Appl. Mater. Interfaces, 2016, 8(39), 25896–25904.
184. N. Ren, B. Chen, R. Li, P. Wang, S. Mazumdar, B. Shi, C. Zhu, Y. Zhao and X. Zhang, Humidity-Resistant Flexible Perovskite Solar Cells with over 20% Efficiency, Sol. RRL, 2021, 5(4), 2000795.
185. Z. Dai, S. Li, X. Liu, M. Chen, C. E. Athanasiou, B. W. Sheldon, H. Gao, P. Guo and N. P. Padture, Dual-Interface-Reinforced Flexible Perovskite Solar Cells for Enhanced Performance and Mechanical Reliability, Adv. Mater., 2022, 34(47), 2205301.
186. H. Zheng, F. Li, Y. Zhang, Y. Meng, S. Gong, C. Zhang and J. Dai, Self-assembled monolayers for improved performance in flexible pin perovskite solar cells, Mater. Today Commun., 2025, 44, 111899.
187. B. Zhou, M. Li, Q. Xiong, L. Zhang, S. Zhang, J. Sun, J. Tang and W. C. Choy, Soft conjugation extension strategy of self-assembled molecules for achieving efficient and mechanically stable flexible perovskite solar cells, Energy Environ. Sci., 2025, 18, 8803–8814.
188. M. Fahim, I. Firdous and W. A. Daoud, Cascade Bridge Interfacial Design for Stable and Sustainable Flexible Perovskite Solar Cells, SusMat, 2025, e70016.
189. Z. Li, C. Jia, Z. Wan, J. Xue, J. Cao, M. Zhang, C. Li, J. Shen, C. Zhang and Z. Li, Hyperbranched polymer functionalized flexible perovskite solar cells with mechanical robustness and reduced lead leakage, Nat. Commun., 2023, 14(1), 6451.
190. Y. Cao, J. Feng, Z. Xu, L. Zhang, J. Lou, Y. Liu, X. Ren, D. Yang and S. Liu, Bifunctional trifluorophenylacetic acid additive for stable and highly efficient flexible perovskite solar cell, InfoMat, 2023, 5(10), e12423.
191. Z. Li, C. Jia, Z. Wan, J. Cao, J. Shi, J. Xue, X. Liu, H. Wu, C. Xiao and C. Li, Boosting mechanical durability under high humidity by bioinspired multisite polymer for high-efficiency flexible perovskite solar cells, Nat. Commun., 2025, 16(1), 1771.
192. Y. Cao, L. Yang, N. Yan, L. Meng, X. Chen, J. Zhang, D. Qi, J. Pi, N. Li and X. Feng, Buried interface modification for high performance and stable perovskite solar cells, Energy Environ. Sci., 2025, 18(8), 3659–3667.
193. D. Liu, H. Zheng, Y. Ahmed, C. Zheng, Y. Wang, H. Chen, L. Chen and S. Li, Enhanced photovoltaic performance of SnO₂ based flexible perovskite solar cells via introducing interfacial dipolar layer and defect passivation, J. Power Sources, 2022, 519, 230814.
194. J. Li, L. Xie, G. Liu, Z. Pu, X. Tong, S. Yang, M. Yang, J. Liu, J. Chen and Y. Meng, Multifunctional trifluoroborate additive for simultaneous carrier dynamics governance and defects passivation to boost efficiency and stability of inverted perovskite solar cells, Angew. Chem., Int. Ed., 2024, 63(14), e202316898.
195. L. Dong, S. Qiu, J. G. Cerrillo, M. Wagner, O. Kasian, S. Feroze, D. Jang, C. Li, V. M. Le Corre and K. Zhang, Fully printed flexible perovskite solar modules with improved energy alignment by tin oxide surface modification, Energy Environ. Sci., 2024, 17(19), 7097–7106.
196. J. Xu, X. Zhu, J. Dai, M. Zhang, X. Wei, T. Lei, H. Xie, Y. Pan, J. Cao and Z. Wu, Improved humidity resistance and bending stability of flexible perovskite photovoltaic module by Incorporating polymerized networks, Chem. Eng. J., 2025, 510, 161624.
197. P. Zhao, Z. Gong, Z. Fang, R. Sun, D. Lin, J. Wu, C. Liu, Q. Ye, P. Guo and H. Wang, Multi-Dimensional Stress Release by Interfacial Embedding of Nanolubricants for Mechanically Stable Perovskite Solar Cells, Adv. Funct. Mater., 2025, 2501166.
198. F. C. Liang, E. Akman, S. Aftab, M. K. Mohammed, H. Hegazy, X. Zhang and F. Zhang, Self-healing polymers in rigid and flexible perovskite photovoltaics, InfoMat, 2025, 7(1), e12628.
199. X. Meng, Z. Xing, X. Hu, Z. Huang, T. Hu, L. Tan, F. Li and Y. Chen, Stretchable perovskite solar cells with recoverable performance, Angew. Chem., Int. Ed., 2020, 59(38), 16602–16608.
200. Z. Chen, Q. Cheng, H. Chen, Y. Wu, J. Ding, X. Wu, H. Yang, H. Liu, W. Chen and X. Tang, Perovskite grain-boundary manipulation using room-temperature dynamic self-healing “ligaments” for developing highly stable flexible perovskite solar cells with 23.8% efficiency, Adv. Mater., 2023, 35(18), 2300513.
201. T. H. Han, Y. Zhao, J. Yoon, J. Y. Woo, E. H. Cho, W. D. Kim, C. Lee, J. W. Lee, J. M. Choi and J. Han, Spontaneous hybrid cross-linked network induced by multifunctional copolymer toward mechanically resilient perovskite solar cells, Adv. Funct. Mater., 2022, 32(40), 2207142.
202. S. Ji, B. G. Hyun, K. Kim, S. Y. Lee, S.-H. Kim, J.-Y. Kim, M. H. Song and J.-U. Park, Photo-patternable and transparent films using cellulose nanofibers for stretchable origami electronics, NPG Asia Mater., 2016, 8(8), e299.
203. C. Jia, X. Zhao, Y.-H. Lai, J. Zhao, P.-C. Wang, D.-S. Liou, P. Wang, Z. Liu, W. Zhang and W. Chen, Highly flexible, robust, stable and high efficiency perovskite solar cells enabled by van der Waals epitaxy on mica substrate, Nano Energy, 2019, 60, 476–484.
204. B. Han, Y. Huang, R. Li, Q. Peng, J. Luo, K. Pei, A. Herczynski, K. Kempa, Z. Ren and J. Gao, Bio-inspired networks for optoelectronic applications, Nat. Commun., 2014, 5(1), 5674.
205. B. Fan, J. Xiong, Y. Zhang, C. Gong, F. Li, X. Meng, X. Hu, Z. Yuan, F. Wang and Y. Chen, A bionic interface to suppress the coffee-ring effect for reliable and flexible perovskite modules with a near-90% yield rate, Adv. Mater., 2022, 34(29), 2201840.
206. R. H. Siddique, G. Gomard and H. Hölscher, The role of random nanostructures for the omnidirectional anti-reflection properties of the glasswing butterfly, Nat. Commun., 2015, 6(1), 6909.
207. S. Zou, Y. Xin, J. Jin, Z. Lin, Y. He, J. Liang, X. Yan and J. Huang, Inverse Opal Photonic Crystal Structured Bifacial-Iridescent Efficient Perovskite Solar Cells and Modules, Adv. Mater., 2025, 37(27), 2420130.
208. Y. Wang, R. Sun, W. Zhao, X. Lu, W. Xiao, F. Meng, X. Zhan, J. Lu, F. Gao and Q. Zhang, Transparent, Anti-Fouling and Mechanically Stable Coating with Hybrid Architecture Inspired by Corn Bracts-Coating Strategy, Adv. Funct. Mater., 2025, 35(15), 2418795.
209. J. Yoon, U. Kim, J. S. Choi, M. Choi and S. M. Kang, Bioinspired liquid-repelling sealing films for flexible perovskite solar cells, Mater. Today Energy, 2021, 20, 100622.
210. P. Wu, J. H. Heo and F. Zhang, Lead chemisorption: Paving the last step for industrial perovskite solar cells, Nano Res. Energy, 2024, 3, e9120093.
211. C. Yang, W. Hu, J. Liu, C. Han, Q. Gao, A. Mei, Y. Zhou, F. Guo and H. Han, Achievements, challenges, and future prospects for industrialization of perovskite solar cells, Light: Sci. Appl., 2024, 13(1), 227.
212. W.-Y. Gao, C.-X. Ran, L. Zhao, H. Dong, W.-Y. Li, Z.-Q. Gao, Y.-D. Xia, H. Huang and Y.-H. Chen, Machine learning guided efficiency improvement for Sn-based perovskite solar cells with efficiency exceeding 20%, Rare Met., 2024, 43(11), 5720–5733.
213. J. Zhang, J. Wu, V. M. Le Corre, J. A. Hauch, Y. Zhao and C. J. Brabec, Advancing perovskite photovoltaic technology through machine learning-driven automation, InfoMat, 2025, 7(5), e70005.
214. Y. Liu, X. Tan, J. Liang, H. Han, P. Xiang and W. Yan, Machine learning for perovskite solar cells and component materials: key technologies and prospects, Adv. Funct. Mater., 2023, 33(17), 2214271.

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