Defect passivation of perovskites for higher efficiency and enhanced stability: applications in solar cells, photoluminescence, and photocatalysis

Abstract

Metal halide perovskites have gained significant attention due to their distinctive photoelectrical properties. However, their sensitivity to some stability stressors has reduced their performance in many fields. The generation of defects has been considered a major contributor to the degradation and low performance of perovskites. Therefore, numerous passivation strategies have been proposed to mitigate the adverse effects of defects. In this review, we present various methods for passivating defects in perovskites, including polymer passivation, bulky organic cations, Lewis acid–base interactions, and metal cations. The effects of passivation on enhancing device performance and improving stability are also discussed. Finally, an outlook is presented to propose novel passivation approaches, especially in photocatalytic applications.

---

Broader context

Metal halide perovskites have rapidly emerged as pivotal materials for solar energy conversion and a wide spectrum of optoelectronic applications due to their exceptional efficiency, low processing cost, and versatile compositional tunability. Their potential extends beyond photovoltaics to promising frontiers such as light-emitting diodes (LEDs), photodetectors, and solar-driven photocatalysis, where superior light absorption and charge transport are paramount. However, the widespread technological deployment of perovskites is critically hampered by their long-term instability under realistic operating conditions. This instability stems from a complex interplay of environmental stressors (moisture, oxygen, heat), intrinsic ion migration, and, fundamentally, defect formation. Defects act as central agents in this degradation, serving as non-radiative recombination centers that limit performance, as channels for ion migration that cause hysteresis and phase segregation, and as nucleation sites for chemical decomposition. This review highlights defect formation as the core determinant of both efficiency losses and operational degradation in metal halide perovskites. It discusses recent, multidisciplinary strategies to mitigate these issues through advanced defect passivation. By consolidating breakthroughs across chemical doping, molecular surface engineering, and interfacial design, this work provides a comprehensive guide for enhancing material durability and electronic functionality. The insights presented are broadly relevant to the development of stable, high-performance perovskite-based technologies—not only in photovoltaics but also in LEDs, photocatalysis, and beyond—thereby accelerating progress toward sustainable and scalable energy and optoelectronic solutions.

1. Introduction

In recent years, metal halide perovskites (MHPs), with the general formula ABX₃, where A is a monovalent organic cation (CH₃NH₃⁺, NH₂CHNH₂⁺, etc.) or an inorganic cation (Cs⁺), B is a divalent metal cation (usually Pb²⁺), and X is a halide anion,¹ have emerged as one of the most promising semiconductors with a wide range of applications. These perovskite structures have shown remarkable applications as solar cells, mainly due to their unique photoelectrical properties, such as high charge-carrier mobility, broad-spectrum light absorption, high light absorption coefficient, and high tolerance to crystal defects.^2–6 Perovskite solar cells (PSCs) have attracted significant attention from scientists due to their impressive photovoltaic properties and low manufacturing costs, comparable to those of traditional silicon-based solar cells.⁷ The power conversion efficiency (PCE) of organic-inorganic PSCs on the lab scale increased dramatically in just 10 years, from 3.8% in 2009 (ref. 8) to 25.5% in 2020 (ref. 9), and more than 26% in recent years.^10–13 Many attempts are ongoing to further enhance the PCE of perovskite solar cells and achieve power conversion efficiencies (PCEs) of up to 27%. (ref. 14) Additionally, a combined analysis based on Shockley–Queisser theory and experimentally achievable photovoltaic parameters suggests that the practical efficiency potential of single-junction PSCs with a band gap of 1.5–1.6 eV could exceed 30%.¹⁵ Achieving this goal requires significantly more effort.

The excellent performance of MHPs was also observed in light-emitting devices (LEDs), as they exhibit an extremely high photoluminescence quantum yield (PLQY) of 100%.¹⁶ They have narrow photoluminescence (PL) peaks with a full width at half-maximum (FWHM) of roughly 12–40 nm, resulting in high purity of color, which is better than that for conventional quantum dot (QD) LEDs.¹⁷ Their emission wavelengths can be tuned across the entire visible and near-IR spectral region by varying the halide composition of perovskites.¹⁸ The first room-temperature perovskite LEDs (PeLEDs) were introduced in 2014 with an external quantum efficiency (EQE) of 0.76%.¹⁹ Since then, several studies have been conducted in this field of perovskite materials, and the EQEs of PeLEDs have been boosted to an incredible 22%.²⁰ Moreover, the synthesis of perovskite materials is straightforward from inexpensive starting materials, potentially decreasing fabrication costs.¹⁸ Due to the above-mentioned outstanding properties, PeLEDs have emerged as potential candidates for next-generation light-emitting devices.

In addition to remarkable applications as solar cells and light-emitting devices, MHPs have recently gained significant attention in photocatalysis, which exploits their unique photophysical properties, including a tunable bandgap, high charge-carrier mobility, and efficient electron–hole separation.² The potential energy gap between the valence and conduction bands of MHPs makes them well-suited to act as photocatalysts in H₂ generation and CO₂ reduction reactions.²¹ Despite these excellent characteristics, industrial applications of metal halide perovskites still suffer from instability. MHPs are highly sensitive to moisture and oxygen; they exhibit poor stability under ultraviolet (UV) radiation, polar solvents (e.g., water), and thermal effects.^22–25 The degradation of conventional perovskites releases heavy metals like lead, inducing significant risks to both the environment and human health while also reducing their optical performance (eqn (1) and (2)):²⁶

Pb(OH)₂ → PbO + H₂O (2)

As a result, it is imperative to develop strategies to produce novel perovskite derivatives with superior optical performance and stability. The studies indicated that halide composition adjustment could significantly improve the stability of perovskites. Noh et al. prepared a CH₃NH₃Pb(I_1−xBr_x)₃ perovskite by substituting I with Br.²⁷ Compared to the standard material CH₃NH₃PbI₃ (MAPbI₃) (x = 0), the stability of perovskite solar cells containing Br was significantly improved.²⁸ The mixed-halide perovskite CsPb(Br_xCl_1−x) was reported to have better stability than CsPbBr₃. Thus, their activity in CO₂ photoreduction was dramatically improved. The total formation rate of CO and CH₄ was approximately 4.5 times higher than that of the pristine CsPbBr₃. Knezevic et al. reported that adjusting the bandgap of CsPbBr₃ covered by a thin layer of porous TiO₂ via anion substitution at room temperature improves stability and enables reaching optimal charge-carrier separation and stabilization in aqueous media for 3 hours.²⁹ The encapsulation of CsPbX₃ into mesoporous silica films with a chiral nematic structure could enhance the perovskites' stability under ambient conditions.³⁰ In addition to conventional three-dimensional (3D) structures, MHPs were found to exist as two-dimensional (2D) structures. The 2D perovskites were shown to maintain unchanged optical properties in water.³¹ The exposure of 2D perovskite structures to 52% relative humidity during 46 days indicated no significant decomposition, while 3D perovskites showed new reflection peaks in X-ray diffraction (XRD) patterns, indicating the segregation of MHP and the formation of PbI₂.32 As a result, solar cells fabricated from (PEA)₂(MA)₂[Pb₃I₁₀] perovskite 2D materials exhibit higher moisture resistance than devices containing 3D materials. In photocatalytic applications in water, 2D MHP nanosheets show greater photocatalytic activity for CO₂ reduction compared to traditional MHP nanocrystals.³¹ The PeLEDs that used quasi-2D perovskite film were also reported to show higher current efficiency and luminance than the 3D perovskite-based technology.

Nevertheless, the performance advantage of a given dimensionality is strongly dependent on the reaction environment. In non-aqueous media, 3D perovskite nanocrystals can outperform 2D nanosheets, as exemplified by CO generation rates that are 3.8 times higher for 3D nanocrystals, which also exhibit higher photoluminescence quantum efficiency (PLQE).³³ These observations indicate that while reduced dimensionality improves stability and surface passivation in aqueous systems, it does not universally guarantee superior photocatalytic activity across all media. Elemental doping provides a powerful strategy to tune both the structural dimensionality and electronic properties of MHPs. In our work, Cu²⁺ doping preserves the three-dimensional framework of CsPbBr₃, whereas Bi³⁺ doping induces a transformation toward a two-dimensional structure. In toluene oxidation, due to an organic solvent environment, Cu-doped 3D CsPbBr₃ exhibits superior photocatalytic activity compared with Bi-doped 2D CsPbBr₃.34 This comparison underscores a wider array of doping strategies. The introduction of extrinsic species can modify the electrical doping of the perovskite film.³⁵ Such changes may arise from intrinsic defect doping, extrinsic impurity incorporation, or charge transfer between the passivating species and the perovskite lattice.³⁶ These processes can change the concentration of free carriers and adjust the Fermi level, thereby affecting the electronic properties of the perovskite film. Additionally, changes in defect distributions may promote ionic migration pathways within the perovskite lattice, thereby further influencing local carrier density and accelerating interfacial degradation under operational conditions.³⁷

Encapsulating MHPs with an overlayer has been shown to be highly effective in protecting their surfaces, thereby significantly increasing their stability in air and water. Li et al. successfully increased the stability of CH₃NH₃PbI₃ perovskite solar cells by spin-coating the surface with butylphosphonic acid 4-ammonium chloride (4-ABPACl).³⁸ The Wentao group reported the successful preparation of CsPbBr₃ nanocrystals coated with a polymer, polyaniline (PANI), which can maintain their stability for approximately 11 days in air.³⁹ Metal oxides such as SiO₂ were used to encapsulate CsPbBr₃ quantum dots (QDs), and it was found that the photoluminescence (PL) of CsPbBr₃@SiO₂ powders remained almost unchanged after 40 days of storage under ambient conditions, and their PL intensity was maintained at 80% after they were continuously illuminated under a UV lamp for 108 hours.⁴⁰ Our group showed that encapsulating CsPbBr₃ with a TiO₂ overlayer enhances the stability of H₂ generation in aqueous solutions.²⁹

The stability affecting MHPs also stems from defects. Defects in semiconductor crystals are either interruptions to the perfect crystal lattice or the presence of foreign atoms (impurities) in the lattice, and they can have cascading effects on device performance, as shown in Fig. 1.^41,42 Defects are usually categorized into three types, which are (1) intrinsic point defects, such as atomic vacancies (missing atoms), interstitials (extra atoms), impurity (foreign atoms) and anti-site substitutions (wrong lattice sites) (Fig. 1a);⁴² (2) two-dimensional defects, for example, dislocation and grain boundaries (GBs) (Fig. 1b); and (3) three-dimensional defects like precipitates and metal clusters (Fig. 1c).^41,43 The concentration of point defects in perovskites is usually higher than that of other types, since their formation energy is much higher.⁴⁴ From point defects to three-dimensional defects, these imperfections influence key material parameters, including trap states, carrier recombination, and surface activity.^45–49 These changes directly affect device performance, including optoelectronic efficiency, photocatalytic activity, and overall stability.

Fig. 1 Left: different forms of defects: (a) intrinsic point defects, (b) two-dimensional defects, and (c) three-dimensional defects, and the influence of the defect on device parameters and performance; middle: the effects of defects on different parameters of materials; right: the impacts of defects on the device's performance.

The defects mainly arise from the rapid crystallization and growth processes of the perovskite films, since these steps are very difficult to control fully.⁷ For example, grain boundaries form during the crystallization process when multiple crystallites grow but do not perfectly align. Other possible causes of perovskites' defects could be (i) a non-stoichiometric ratio of the starting materials (e.g., lead, halide, organic cations); (ii) environmental factors (e.g., air, moisture, light); and (iii) processing conditions (e.g., solvent systems, synthesis methods, temperature).⁵⁰ For instance, the diffusion of Ag⁺ or Au⁺ from the electrode into perovskite layers in solar cells can introduce impurity defects, or the reduction of Pb²⁺ to Pb⁰ during the synthesis process is associated with a precipitation defect.

Defects play an essential role in controlling the optoelectrical and structural properties of perovskite materials. Therefore, they drastically influence the optical performance of MHPs. Defects can provide several benefits, such as active photocatalysis sites and holes for charge transport. On the other hand, defects can be detrimental because they introduce trap states in the band gap, which may act as centers for nonradiative recombination, reducing the photoluminescence performance and stability of perovskites.⁵¹ As a result, eliminating the negative impacts caused by defects will be a key step to further enhance the stability and the overall performance of perovskites. The preparation of single-crystalline perovskite materials can be a solution for defect problems since single-crystalline perovskites are free of grain boundaries and have a low density of defects compared to polycrystalline perovskites.⁴³ However, it is challenging to synthesize single-crystal perovskite materials with suitable device-scale thickness. Therefore, defect passivation is expected to be the most efficient method for mitigating the negative effects of defects in perovskites.

In this review, we will summarize different strategies for defect passivation in metal halide perovskites, including passivation by organic ions, Lewis acids and bases, and metal ions. The mechanism for passivating the negatively and positively charged defects will be shown. Their effect on increasing the stability of perovskite materials will also be discussed, focusing on improving their optical performance and applications in solar cells, light-emitting diodes, and photocatalysis.

2. Defect passivation by organic molecules

In the process of advanced perovskite materials, a range of organic additives has been used to improve film morphology, interfacial properties, and long-term device stability. These additives operate through different mechanisms and therefore need to be discussed according to their functional roles.

Polymeric and biopolymeric materials, such as PMMA and chitosan, are often employed as coating or encapsulation agents.^52,53 Because nanoparticles and microparticles typically possess high surface energy and are prone to forming fissured domains, polymer coatings can effectively reduce surface roughness and enhance interfacial wettability at the polymer–polymer junction between the perovskite layer and the hole transport layer (HTL).^54,55 In addition, polymer matrices can encapsulate physically perovskite grains and grain boundaries, thereby limiting ion migration pathways and providing partial protection against environmental factors such as moisture and oxygen. These effects improve device performance and operational stability.

In contrast, organic ammonium salts or bulky organic cations interact more directly with the perovskite crystal lattice. By intercalating between the inorganic octahedral layers, these species can promote the formation of layered or quasi-two-dimensional (2D) perovskite structures or 2D/3D heterostructures. Such architectures enhance resistance to ion migration and environmental degradation while preserving the crystalline framework of the light-absorbing material. However, due to their relatively insulating nature, excessive incorporation may hinder charge transport and reduce device performance.⁵⁶

Another important class of additives includes small-molecule ligands, which function by passivating chemical defects. These molecules can coordinate with under-coordinated metal ions or compensate ionic defects at surfaces and grain boundaries, thereby suppressing trap states and reducing non-radiative recombination losses.⁵⁷ Organic molecules may also introduce additional functionalities into perovskite systems; for example, additives such as ethylene glycol have been reported to induce self-healing behavior or enable property tuning in composite structures.⁵⁸

Given the diversity of molecular structures and mechanisms involved, it is useful to classify organic molecules according to their primary functional roles. The following sections discuss organic additives in two main categories: (i) organic capping ligands, which mainly regulate surface chemistry and interfacial interactions, and (ii) defect passivation agents based on Lewis acid–base interactions, which aim to suppress electronic defects in perovskite films.

2.1 Organic capping ligands

Metal halide perovskite nanocrystals can be synthesized by a hot-injection method, which involves injecting Cs-oleate into a solution containing lead salts in oleic acid (OA), oleylamine (OAm), and octadecene (ODE). These capping ligands are essential in preparing perovskites since they are responsible for colloidal stability and shape control.⁵⁹ Organic capping ligands can improve surface characteristics. It would need more research in terms of surface modification of perovskites for different applications. Meanwhile, long-chain OA/OAm ligands could easily desorb from the surface of perovskites, generating several defects,² and can further lead to halide migration and segregation, inducing the decomposition of perovskites.

These surface defects not only cause the structural integrity of perovskites but also affect their optoelectronic and catalytic performance. Particularly, OA/OAm-capped perovskites are unfavorable for CO₂ photoreduction since the long-chain capping ligands hinder efficient charge separation on the surface of MHPs and thus decrease the photocatalytic performance.² Therefore, developing novel ligands capable of passivating surface defects and improving the stability of perovskite nanocrystals (NCs) is imperative, as replacements for the traditional long-chain OA/OAm.

In 2022, Li et al. employed the reactive thionyl bromide (SOBr₂) to replace the original ligands (OA/OAm) and compensate for bromine vacancies on CsPbBr₃ nanocrystals (Fig. 2a).⁶⁰ This approach aimed to enhance stability while also facilitating charge transfer and separation from CsPbBr₃ to g-C₃N₄. As a result, CsPbBr₃–SOBr₂ NCs exhibited elevated CO₂ photoreduction activity. The photocatalytic yield is 69 µmol g⁻¹ h⁻¹ in terms of electron consumption, which was approximately six times higher than that of pristine CsPbBr₃. Furthermore, when combined with g-C₃N₄, the CO₂ photoreduction yield reached an even higher value of 190 µmol g⁻¹ h⁻¹. The utilization of tetrafluoroborate salts (BF⁴⁻) was reported as a defect treatment agent with subsequently loaded Co²⁺ as a co-catalyst (Fig. 2b).⁶¹ The results demonstrated that CsPbBr₃–BF₄ exhibited high photocatalytic CO₂ performance, with CO and CH₄ evolution rates of 83.8 µmol g⁻¹ h⁻¹.

Fig. 2 (a) Schematic representation of SOBr₂ ligand modified-CsPbBr₃ NCs. Reproduced with permission.⁶⁰ Copyright 2022, American Chemical Society. (b) Schematic representation of the treatment of CsPbBr₃ with BF₄⁻/Co²⁺ ions. Reproduced with permission.⁶¹ Copyright 2021, Wiley-VCH GmbH. (c) Schematic representation of surface passivation by IDA (left); the PLQYs of OA-treated and IDA-treated CsPbX₃ NCs and EQE of corresponding PeLED devices (right). Reproduced with permission.⁶² Copyright 2017, American Chemical Society.

Because surface treatment can adjust the surface characteristics of the perovskites, a post-synthesis approach was proposed to passivate the surface defects of CsPbBr₃ nanocrystals by using a bidentate ligand 2,2′-iminodibenzoic acid (IDA) (Fig. 2c).⁶² The IDA ligand was found to be a key compound, showing much stronger binding to the perovskite surface than the OA ligand does, which can be attributed to strong interactions between the dual carboxylic groups and undercoordinated Pb²⁺ sites. The two carboxyl groups of IDA can simultaneously coordinate to surface Pb²⁺ centers, forming a bidentate chelate at the nanocrystal surface. Compared with monodentate ligands like OA, this chelating coordination offers stronger interfacial binding, helping reduce ligand desorption or dynamic surface ligand exchange during storage. The surface trap density decreased, and additional electrons were injected into perovskite NCs. The enhanced surface coordination structure helps maintain the passivated surface state, which reduces the reformation of undercoordinated sites and defect-assisted nonradiative recombination over time. The stability of the cubic perovskite phase and electronic coupling between ligands and NCs were remarkably improved. In this work, the IDA-treated CsPbX₃ NCs exhibited an excellent PLQY of 95%, compared to 80% recorded for the pristine ones, as illustrated in Fig. 2c. Consequently, the EQE of the red LED device based on IDA-treated CsPbI₃ NCs reached a maximum value of 5%, which was almost 2-fold higher than that of the control device. Stability tests also revealed that IDA-treated NCs showed significantly improved stability, with no phase change after 40 days. Moreover, IDA-treated NCs retained 90% of PL emission after 15 days, and the PLQY remained almost the same after washing with ethyl acetate. The persistence of surface-bound IDA species after antisolvent washing, in contrast to the pronounced ligand loss observed for OA-capped nanocrystals, was supported by Fourier-transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses.

2.1.1 Organic ammonium cations. Organic ammonium cations have been employed by many groups for perovskite defect passivation because they can readily form ionic bonds with uncoordinated ions, thereby healing defects within the perovskite crystal lattice. For instance, a straightforward method was reported to reduce the level of electronic defects at the interface between the perovskite film and the hole transport layer (HTL). To do so, the surface of the perovskite was modified via the addition of organic ammonium salts, including ethylammonium iodide (EAI), imidazolium iodide (IAI), and guanidinium iodide (GuaI).⁶³ Introducing salts prevented the irreversible decomposition of perovskites by fixing the A-site cation defects and enhancing the stability of the perovskite absorber. The photovoltaic devices fabricated from EAI-, IAI-, and GuaI-perovskite showed significantly improved photoconversion performance compared to the original devices, with great power conversion efficiencies up to 21.0%.

The defects' passivation by ammonium salts further increased the operational stability of perovskite solar cells, with a minor 5% efficiency loss in the best-performing devices after 550 h of exposure to maximum-power solar-intensity conditions (Fig. 3a). The Gua cation (or GA) was employed to mitigate surface defects and enhance the stability of other types of perovskites.⁶⁴ The surface-stabilizing 1,3,5-tris(bromomethyl)-2,4,6-triethylbenzene (TBTB) was used as a healing agent for bromide vacancy (Fig. 3b).⁶⁵ As a result, the PLQY of the passivated perovskite increased from 79.7% for the pristine MHP to 93.3%, and the performance of the green LED improved, with a high current efficiency of 108 cdA⁻¹ and an impressive EQE of 23.4% being achieved. Liang et al. synthesized a series of phenyl and thienyl-based ammonium salts as the passivators for perovskites, including phenylethylammonium iodide (PMAI), thienyl methyl ammonium iodide (TMAI), phenyl formamidinium iodide (PFAI), thienyl formamidinium iodide (TFAI), phenyl imidazolium iodide (PImI), and thienyl imidazolium iodide (TImI)⁶⁶ (Fig. 3c). These passivators effectively passivated surface defects in as-prepared perovskite thin films, thereby enhancing optoelectronic properties and PLQY by reducing non-radiative recombination.

Fig. 3 (a) Operational stability over time of the control and treated perovskite devices regarding power conversion efficiency. The devices were exposed to constant illumination (LED source, ∼1 sun) at the maximum power point for 550 h. Reproduced with permission.⁶³ Copyright 2019, Nature Communications. (b) Schematic representation of the DFT-proposed mechanism for bromide vacancy passivation driven by TBTB molecules on the GA-terminated FAPbBr₃ surface. Reproduced with permission.⁶⁵ Copyright 2021, Nature Photonics. (c) The molecular structures of different phenyl and thienyl-based ammonium salts as the passivators for perovskites (left); operational stabilities of the PMAI- and PImI-treated devices tested at a constant current density of 10 mA cm⁻² (right). Reproduced with permission.⁶⁶ Copyright 2021, Wiley-VCH GmbH.

The introduction of the passivators also decreased the grain size and surface roughness of perovskite films. The passivated PeLEDs exhibited good color stability with no wavelength shift observed in the electroluminescence spectra under different applied bias voltages. The highest EQE of 15.6% was recorded for the MAPbI₃-based LEDs treated with PImI passivators, which was ten times higher than that of the pristine MAPbI₃ control device. Moreover, the treatment with PImI passivators significantly improved the operational stability of the PeLEDs. The results suggested that the PImI-based device retained 50% of its initial EQE after 2 h under a constant current density of 10 mA cm⁻², whereas the device treated with PMAI lasted only 6 min under the same conditions. To passivate the Br defect and increase the water resistance of the conventional perovskites, the diethylenetriamine ion (DETA³⁺) can be utilized in some cases.⁶⁷

2.1.2 Dual passivation using zwitterionic molecules. Organic cationic or anionic passivators can only act on a single defect at a time, limiting their applicability, as perovskites typically possess multiple defects. Therefore, using a zwitterionic passivator (Zw), which can heal both positive and negative defects, introduces a novel approach to enhance passivation efficiency.

A dual passivation method has been reported for perovskite defects using a bifunctional molecule, such as 4-fluorophenyl methyl ammonium trifluoroacetate (FPMATFA).⁶⁸ The FPMA cations and TFA anions can form electrostatic bonds with uncoordinated lead and halide ions, respectively. Zwitterionic passivators can simultaneously passivate both lead and halide defects, as shown in Fig. 4a. Consequently, the fabricated PeLEDs achieved an EQE of 20.9% at an excitation wavelength of 694 nm. Moreover, due to defect passivation, the FPMATFA-passivated films exhibited better thermal and optical stability than the pristine FPMAI_0.7Br_0.3 film. The FPMATFA device also demonstrated higher storage stability, with its EQE showing no degradation after 2 months. Similarly, 3-(decyldimethylammonio) propane-sulfonate (DPSI), a sulfonic zwitterion salt, was selected for passivating the perovskite's defects.⁶⁹ A small amount of DPSI salt (0.05 wt%) was introduced into the MAPbI₃ precursor solution. The ammonium groups in DPSI formed ionic bonds with MA vacancies, while sulfonic groups combined with iodine vacancies to simultaneously passivate negatively and positively charged defects at the perovskite surface and grain boundaries (Fig. 4b). The strong coordination of the S=O group in DPSI with Pb ions also passivated morphological defects during the fabrication process of the perovskite film. The stability of DPSI-treated PSC devices was then examined by exposing them to continuous AM 1.5 G illumination. The DPSI devices maintain 88% of their initial performance after 480 h, indicating their high stability under UV radiation. Moreover, the treated devices showed excellent moisture resistance, retaining 96% of their initial performance after the 60 h test under relative humidity (RH) conditions in the range of 30–70%. After the passivation, formation of the pinhole as a morphological defect was inhibited, thus decreasing the charge trap density and extending the electron–hole recombination lifetime. As a result, the efficiency of PSCs was boosted to an impressive value of 21.1%.

Fig. 4 (a) Schematic representation of defect passivation at perovskite grain boundaries by FPMATFA. Reproduced with permission.⁶⁸ Copyright 2020, WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. (b) Schematic representation of DPSI mediated perovskite growth and defect passivation.⁶⁹ Copyright 2020, WILEY-VCH Verlag GmbH & Co. KGaA, Wienheim. (c) Schematic representation of passivation of I vacancies by 3-(1-pyridinio)-1-propanesulfonate. Reproduced with permission.⁷⁰ Copyright 2018, the Royal Society of Chemistry. (d) Schematic representation of the reaction process from the precursor to monolithic perovskite grains. Reproduced with permission.⁷¹ Copyright 2019, the Royal Society of Chemistry. (e) Device configuration for the ETL–cathode interface by employing rhodamine. Reproduced with permission.⁷² Copyright 2017, the Royal Society of Chemistry.

In the same context, perovskite solar cells were treated with a 3-(1-pyridinio)-1-propane sulfonate zwitterion to increase their thermal stability and power conversion efficiency⁷⁰ (Fig. 4c). The sulfonic group in the zwitterion was bonded to the SnO₂ surface to modify the SnO₂ electron transport layer (ETL), thereby increasing electron transport mobility and preventing charge recombination. The sulfonate group can strongly anchor to surface hydroxyl groups and undercoordinated metal sites on SnO₂, resulting in an interfacial coordination structure. Meanwhile, the positively charged N atoms healed Pb–I antisite defects to improve the stability of PSC devices. The zwitterionic molecular structure simultaneously interacts with both the SnO₂ ETL and the perovskite surface, thereby helping reduce interfacial ion migration, interfacial bond dissociation, and defect re-formation under thermal and humid stress. Consequently, the Zw–SnO₂-based PSC device showed great thermal stability, maintaining 80% of its initial efficiency after 60 min under heating at 150 °C. Furthermore, the Zw–SnO₂-based device exhibited long-term stability, retaining 93% of its initial performance after 140 h under harsh conditions (85 °C, 85% RH). These findings indicate that zwitterion-derived interfacial passivation remains stable even under harsh aging conditions, enabling effective interfacial charge extraction and mitigating thermally induced interfacial degradation. With further optimization, the modified perovskite solar cells exhibited PCEs of up to 21.43%. Yang et al. treated an MAPbI₃ precursor with ammonium benzenesulfonate (ABS) to produce high-quality PSCs (Fig. 4d). Due to the zwitterionic structure, ABS can simultaneously passivate cationic and anionic defects at grain boundaries, thus considerably reducing the trap density in the perovskite. The fabricated device achieved the highest PCE of 20.62% and showed great moisture stability, with only 15% efficiency loss after storing for 1400 h under ambient conditions.⁷¹ Other groups also employed the introduction of zwitterions onto the charge transport layer. For example, Ciro et al. utilized Rhodamine derivatives to passivate the defects on the ETL of perovskite solar cells⁷² (Fig. 4e). The charge transport efficiency was thereby improved, and the moisture stability of MHPs was also increased since Rhodamine can act as a barrier that prevents the penetration of moisture into the perovskite layer. Therefore, an increase in PCE to 16.6% was obtained.

The zwitterionic amino acid, for example, L-alanine, can be used as an additive in the perovskite precursor solution to passivate both positively and negatively charged defects.⁷³ Under specific pH conditions, positively charged NH³⁺ and negatively charged COO⁻ functional groups effectively passivated both cation and anion defects in MAPbI₃ PSCs (Fig. 5a), increasing perovskite grain size and extending charge-carrier lifetime. This enhancement resulted in an improvement of PCE from 18.3% without the additive to 20.3%. Moreover, the ionic defect passivation method affected the stability of PSCs. The L-alanine-treated device retained nearly 90% of its initial PCE after 16 h of photoirradiation. In comparison, the PCE of a pure device dropped rapidly to 80% of its initial PCE after the same period (Fig. 5b). Therefore, using the zwitterionic form of amino acids, the dual passivation method is an effective way to heal MHPs' ionic defects and fabricate highly stable PSCs. This approach was employed by many other groups with different amino acids, such as (s)-(−)-4-amino-2-hydroxybutyric acid (AHBA) molecules,⁷⁴ which can efficiently passivate the traps/defects at grain boundaries and the surface of perovskite via coordination with uncoordinated lead and iodide ions (Fig. 5c). The COO⁻ group coordinates with undercoordinated Pb²⁺ sites, while the –NH₃⁺ group forms hydrogen bonds with iodide ions (N–H⋯I). Additionally, the –OH group provides additional hydrogen bonding interactions (O–H⋯I). These interactions were confirmed by XPS, which showed shifts in the binding energies of Pb 4f, I 3d, N 1s, and O 1s, indicating chemical coordination between AHBA and the perovskite lattice. The multifunctional molecular structure of AHBA offers multiple interaction sites at grain boundaries and surfaces, which is expected to enhance interfacial coordination and minimize defect reactivation during long-term storage. The PCE was thus boosted from 17.96% to 20.31%, and the intrinsic stability of the devices was also improved, which retained 94% of their initial performance after 60 days of storage in an N₂ atmosphere.

Fig. 5 (a) Schematic representation of the planar p–i–n device architecture and a possible passivation mechanism of the L-alanine additive in the perovskite film. Reproduced with permission.⁷³ Copyright 2020, Wiley-VCH GmbH. (b) Normalized PCE as a function of time and photographs of the perovskite films with and without the L-alanine additive, which were exposed to 1 sun illumination in the air (inset). Reproduced with permission.⁷³ Copyright 2020, Wiley-VCH GmbH. (c) AHBA-passivation at the perovskite surface and grain boundaries through coordination with undercoordinated Pb²⁺ and iodide-related defects.⁷⁴ Copyright 2020, Royal Society of Chemistry.

2.1.3 Organic ammonium cations as a spacer of low-dimensional perovskite overlayers. In addition to passivating defects via electrostatic interactions, organic ions, such as bulky organic ammonium cations, can form new layered perovskites, reducing recombination between light-absorbing and charge-transporting layers in PSCs. These layered perovskites have also been reported to improve MHPs' stability. For example, the incorporation of hydrophobic long-chain organic cations, such as phenylethylammonium (PEA⁺), generated a 2D perovskite layer on the surface of MAPbI₃ (Fig. 6a), which could act as a moisture barrier and thus increase the moisture stability of perovskites. The power conversion efficiency of PSCs was also boosted to 16.8% due to the enhanced open-circuit and fill factor.⁵⁷ A mixed passivation strategy was presented to passivate the perovskite/HTL interface using iso-butylammonium iodide (iBAI) and formamidinium iodide (FAI) (Fig. 6b) to enhance both the power conversion efficiency and the stability of (FAPbI₃)_0.85(MAPbBr₃)_0.15 PSCs.⁷⁵ Upon optimizing the molar fraction of FAI and iBAI, the number of defects on the perovskite surface decreased, which can be attributed to the reaction between iBAI and excess PbI₂, forming a 2D iBA₂PbI₄ passivation layer at the perovskite/HTL interface. FAI can react with PbI₂ to passivate the FA or I vacancies. The passivation layer could inhibit ion migration and interfacial trap filling, thereby reducing hysteresis. Moreover, the formation of the iBA₂PbI₄ layer introduces a hydrophobic organic barrier that can retard the ingress of moisture into the underlying perovskite film. While hydrophobicity itself is not a defect passivation mechanism, it may enhance environmental stability by limiting water-induced degradation pathways. Stability tests of solar cell devices were carried out by storing the devices at 75% RH. After 38 days, the passivated devices exhibited moisture stability two times higher than the original ones. The PCE was thus boosted to a remarkable value of 21.7%.⁷⁵ Tavakoli et al. selected formamidinium chloride (FACl) and 1-adamantylamine hydrochloride (ADAHCl) for the mixed passivation method of the perovskite surface.⁷⁶ FACl served as a chlorine source with better solubility than other precursors such as MACl or PbCl₂, facilitating the efficient replacement of MA⁺ ions with FA⁺ ions, resulting in higher crystallinity and stability of the perovskite. Following the annealing process, Cl in FACl was released from the perovskite absorber surface via volatilization, generating surface defects (Fig. 6c). Therefore, ADAHCl was used as an additive Cl source to passivate the perovskite surface and further improve perovskite film quality by preventing surface recombination. This passivation strategy boosted the PCE of perovskite solar cells to 21.2%. The Cl-treated PSC exhibited better stability than the reference device, as its PCE maintained 88% after 700 h under continuous illumination.⁷⁶

Fig. 6 (a) Schematic representation of the crystal structures of methylammonium lead iodide (MAPI) and a layered perovskite (LPK), forming a junction. Reproduced with permission.⁵⁷ Copyright 2016, American Chemical Society. (b) Schematic representation of the MP passivation treatment method with FAI and iBAI. Reproduced with permission.⁷⁵ Copyright 2018, WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. (c) Schematic representation of perovskite films fabricated by the antisolvent method on SnO₂-coated FTO glass before and after treatment with ADAHCl and FACl. Reproduced with permission.⁷⁶ Copyright 2019, WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

2.2 Defect passivation by Lewis acids and bases

Organic ions exhibited excellent defect passivation properties due to strong electrostatic interactions or ionic bonds with uncoordinated cations and anions within the perovskite crystal structure. Besides, Lewis acids and bases have also been reported to effectively passivate many defects in metal halide perovskite crystals. Lewis bases with strong electron-donating atoms, such as nitrogen and oxygen, can passivate the positively charged defects on the surfaces and grain boundaries (GBs) of perovskite layers. At the same time, Lewis acids can act as passivators of defects with lone-pair electrons, such as I⁻ ions and PbI₃⁻ antisite defects (Fig. 7).

Fig. 7 Schematic representation of defect passivation by Lewis acids and bases.

2.2.1 Nitrogen-based Lewis base passivators. Amine-based passivating materials (APMs) are the most typical Lewis bases for defect healing in MHPs, mainly due to the strong coordination between nitrogen atoms and lead ions. For example, Lee et al. reported the treatment of MAPbBr₃ with ethylenediamine (EDA) to enhance the performance of perovskite light-emitting diodes.⁷⁷ The lone pairs of N atoms formed a strong coordinate bonding with uncoordinated Pb atoms, thus passivating the defect sites in MAPbBr₃. After introducing EDA, the perovskite films exhibited enhanced PL intensities, longer PL lifetimes, and reduced PL blinking, due to the inhibition of non-radiative charge-carrier recombination. Furthermore, improved surface passivation and enhanced interfacial coverage can mitigate ion accumulation at the perovskite/metal interface, thereby suppressing electrode corrosion. However, this treatment mainly improves interfacial stability rather than completely eliminating intrinsic bulk ion migration. The stability of APMs' devices was significantly improved, with almost no color change in the Ag electrode after 30 days of continuous operation (Fig. 8a). XPS and XRD analyses further confirm that the interfacial passivation structure remains stable during long-term aging. The absence of AgBr-related signatures in the APM-treated samples after 30 days indicates that the passivated surface effectively suppresses halide migration from the perovskite layer to the metal electrode. This ongoing inhibition of ion transport suggests that the interfacial coordination environment established by the APMs is resistant to structural disruption under ambient conditions. As a result, highly efficient and stable PeLEDs were obtained, with the highest EQE of 6.2%.⁷⁷ Wang et al. selected phenylalkylamine, including aniline (A), benzylamine (BA), and phenethylamine (PA), as APMs for FAPbI₃ films.⁷⁸ The amino groups passivated the undercoordinated Pb site defects by coordinating with Pb ions or forming hydrogen bonds with I ions. Moreover, the benzene rings exhibited strong hydrophobicity and formed an ordered edge-on packing in benzylamine-modified FAPbI₃ films. Cooperative interactions between amino groups and surface ions, along with the ordered molecular packing of benzyl moieties, are expected to enhance the stability of the surface coordination structure by reducing molecular desorption, preventing surface rearrangement, and minimizing moisture-induced disruption during long-term aging. The perovskite films showed almost no degradation after more than 2900 h of air exposure under an RH level of 50 ± 5%, as presented in Fig. 8b. BA-modified films showed significantly better moisture stability compared to PA-modified films, despite the fact that the two molecules differ by only one additional –CH₂– group. This finding suggests that long-term stability is heavily influenced by the molecular configuration and structural integrity of the passivation layer rather than solely by the presence of amine functional groups. The electronic properties of MHPs were simultaneously enhanced, resulting in a significant increase in PCE to reach 19.2%.⁷⁸ Benzylamine (BA) was further employed to fabricate high thermal-photostability and photovoltaic performance PSCs.⁷⁹ After the treatment with BA molecules, the defects on the perovskite film surface and GBs were effectively passivated, thereby inhibiting phase transformation and perovskite decomposition. The BA-treated PSCs showed greatly enhanced thermal- and photostability. The PL mapping image showed that the pristine film had already turned dark after 8 h of exposure to white LED illumination at 85 °C, whereas the BA-treated film showed only minor changes in its PL emission under the same conditions (Fig. 8c). Owing to these advantages, the BA-treated solar cells exhibited high photovoltaic performance, with a champion efficiency of 17.1%.

Fig. 8 (a) Stability test of the Ag electrode on MAPbBr₃ materials with and without APMs under ambient conditions over time. Reproduced with permission.⁷⁷ Copyright 2017, American Chemical Society. (b) Stability test of pristine FAPbI₃, A-FAPbI₃, BA-FAPbI₃, and PA-FAPbI₃ films under different durations (fresh, 3 days, and 4 months) of exposure under 50 ± 5 RH% air. Reproduced with permission.⁷⁸ Copyright 2016, WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. (c) PL mapping for pristine and BA-treated films aged for 8 h under a white LED light source with an intensity of 200 mW cm⁻² at 85 °C. Reproduced with permission.⁷⁹ Copyright 2017, WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. (d) XRD pattern of HMTA-perovskites after exposure for 10 days under ambient air with a relative humidity of 55%. Reproduced with permission.⁸⁰ Copyright 2017, Elsevier B.V. (e) Normalized PCE of pristine and melaminium-treated perovskites over time under RH of 65% in the dark. Reproduced with permission.⁸¹ Copyright 2018, American Chemical Society. (f–i) Scanning electron microscopy (SEM) images of the pristine perovskite (control) and melaminium-treated perovskite (x = 0.01) after 24 h under RH of 65% in the dark. Reproduced with permission.⁸¹ Copyright 2018, American Chemical Society.

Zheng et al. reported that a tertiary amine, hexamethylenetetramine ((CH₂)₆N₄, HMTA), had a positive effect on stabilizing perovskites.⁸⁰ HMTA can form a strong Pb–N bond, passivating grain boundary defects and preventing the formation of PbI₂ as a decomposition product. Simultaneously, HMTA treatment inhibited water adsorption at the surface and enhanced the water resistance of perovskite solar cells. The HMTA-perovskite showed a very weak PbI₂ peak in the XRD pattern after 10 days of air exposure, indicating much lower degradation (Fig. 8d). Moreover, HMTA enhanced the binding between the perovskite layer and the ZnO ETL, thereby improving interfacial charge transport. As a result, the PCE of HMTA-treated PSCs increased significantly from 12.70% to 17.87%.⁸⁰ Kim et al. reported the introduction of melaminium iodide into a perovskite precursor solution. Besides the coordination of the –NH₂ group with PbI₂, the –C=N– group in the melamine ring interacted with the FAI impurity via hydrogen bonding, thus healing the defects on the surface of perovskites and suppressing non-radiative recombination.⁸¹ The photovoltaic performance of melamine-treated PSCs was significantly improved, yielding a PCE of 17.3%, compared to 15.9% for the pristine PSCs. The influence of melamine on the humidity stability of perovskite was also investigated by exposing it to 65% relative humidity (RH) in the dark. The pristine perovskite showed a significant decrease in PCE from 18% to 16.4% during a reverse scan after 96 h of testing. In contrast, the PCE of the melaminium-treated perovskite experienced a much smaller loss, from 18.4% to 17.4% (Fig. 8e). Moreover, the pristine perovskite exhibited significant surface morphological degradation after a 24 h aging test. In contrast, the melamine-modified perovskite exhibited minimal change in the morphology due to the rear-surface passivation and the low aqueous solubility of melamine (Fig. 8f–i). A large hysteresis was observed in the pristine perovskite after 96 h, mainly due to increased trap states resulting from moisture intrusion. This issue was effectively addressed when the melaminium additive was incorporated into the perovskite surface.⁸¹

2.2.2 Oxygen-based Lewis base passivators. Oxygen-containing Lewis bases have been proven to exhibit passivation ability like nitrogen-containing Lewis bases. For instance, a bilateral interfacial passivation strategy by using diphenylphosphine oxide-4-(triphenylsilyl)phenyl (TSPO1) as the passivator was proposed.⁸² The TSPO1 molecules passivated both the top and bottom of the perovskite emitting layer via the interaction between uncoordinated Pb and the P=O functional group (Fig. 9a). By doing so, interfacial nonradiative recombination was significantly suppressed, leading to enhanced PLQY. Consequently, the passivated PeLEDs reached a maximum EQE of 18.7% and a current efficiency of 75 cd A⁻¹. Moreover, the addition of TSPO1 also significantly improved the stability of PeLEDs. The PL emission intensity of bilateral-passivated perovskite films remained above 85% of the initial value after 10 h of continuous irradiation in ambient air with 40% RH. In contrast, pristine films lost 60% of the original efficiency after the same period. As a result, the operational lifetime of passivated PeLEDs was dramatically increased, which was 20 times longer than that of the control device, reaching 15.8 h.⁸² The carbonyl group C=O demonstrated great coordination with lead ions, prompting several studies on its utilization as a perovskite passivator. Wang et al. incorporated theophylline, caffeine, and theobromine into perovskite films and investigated their impact on defect passivation.⁸³ The results indicated that the –C=O group in the xanthine core of the theophylline molecule strongly interacted with the Pb antisite, while the neighboring N–H on the imidazole ring coordinated to PbI₆⁻ via a hydrogen bond, thus passivating the surface defects (Fig. 9b). The PCE of the theophylline-treated device was boosted to reach 23.48%. For caffeine, the hydrogen bond between the xanthine core and PbI₆⁻ was eliminated since a methyl group was linked to N on the imidazole ring. A weak interaction between caffeine and Pb_I defects was obtained, resulting in a decrease in PCE of the caffeine-treated device to 22.32%. When the N–H and C=O groups were located next to each other on the same six-membered ring to form theobromine, the interaction between N–H and I was disabled, leading to an even weaker interaction. The theobromine-treated device exhibited a significant decrease in PCE to 20.24%. The passivated devices also showed long-term stability, with their PCE retaining more than 90% of the initial value after storage at 40% RH for 500 h.⁸³ An organic dye (AQ310) was employed to passivate trap states at the surfaces and GBs of hybrid perovskite solar cells.⁸⁴ The passivation mechanism is due to the coordination of the –COOH group in AQ310 with uncoordinated Pb ions (Fig. 9c). The trap states were thereby reduced, leading to higher stability. Eventually, the PSC with the AQ310 passivator recorded the best power conversion efficiency of 19.43%, 1.5% higher than that of the original PSC.

Fig. 9 (a) Schematic representation of defect passivation by TSPO1. Reproduced with permission.⁸² Copyright the Author(s), 2020. (b) Schematic representation of surface passivation by theophylline, caffeine, and theobromine. Reproduced with permission.⁸³ Copyright Science, 2019. (c) Schematic representation of the passivation mechanism of AQ310. Reproduced with permission.⁸⁴ Copyright 2018, WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

2.2.3 Sulphur-based Lewis base passivators. Besides N-containing and O-containing Lewis bases, many S-containing bases were also investigated to have good passivation effects on perovskites.⁸⁵ For example, two thiophene isomers (named S2 and S3) were used to passivate the defects in PSCs through the strong interaction of S atoms with uncoordinated Pb²⁺ sites.⁸⁶ The coordination between the lone pair of S atoms and the Pb ion slowed down the crystallization process and prevented the migration of ions. The non-radiative recombination and trap density were significantly reduced, while the charge extraction ability improved. The thiophene-functionalized perovskites further showed excellent thermal stability with minimal decomposition observed at 289 °C. Moreover, the introduction of two thiophene isomers improved perovskite's moisture stability, as much lower PbI₂ diffraction intensities were observed in XRD patterns after 14 days at 65 ± 0% RH. Consequently, the highest PCE of 18% was achieved for the S3-passivated device, which was 6.69% higher than that of the reference device (Fig. 10a).⁸⁶ The thiophene-based interlayers, including 3-phenolic acid (TA 1), thiophene-3-acetic acid (TA 2), and 3-thiophene propanoic acid (TA 3), were reported to increase the conductivity and decrease the work function of SnO₂ ETLs in perovskite solar cells.⁸⁵ The sulfur atoms in the thiophene ring can coordinate with the uncoordinated Pb²⁺ ion in MAPbI₃, thereby passivating ionic defects, reducing trap states, and reducing charge-carrier recombination at SnO₂/MAPbI₃ interfaces (Fig. 10b). Meanwhile, the –COOH groups of the thiophene-based interlayers chemically anchor to the SnO₂ surface and passivate surface –OH dangling bonds, improving the electrical properties of the electron transport layer. In addition, treatment with thiophene-based interlayers improves perovskite crystallinity, resulting in larger grain size and lower defect density. The TA interlayer-modified PSCs also showed better thermal stability, retaining roughly 80% of the initial PCE after 130 h of thermal annealing at 85 °C. As a result, the TA 1, TA 2, and TA 3 interlayer-modified MAPbI₃ achieved PCEs of 19.59%, 18.67%, and 20.61%, respectively, compared to 17.54% of the original one.⁸⁵ Apart from thiophene and its derivatives, another example of an S-containing passivator was p-mercaptobenzoic acid (HOOC-Ph-SH), which was introduced into the TiO₂/MAPbI₃ interface.⁸⁷ The carboxylic group of the passivator was coordinated with TiO₂, while the –SH group was combined with Pb on the perovskite absorber, facilitating electron transfer from the perovskite to TiO₂ and increasing the photovoltaic performance of PSCs (Fig. 10c). Moreover, the perovskite surface was modified with the highly hydrophobic pentafluorobenzenethiol (HS-PhF₅). HS-PhF₅ covered the perovskite surface via the coordination of Pb–S, inhibiting the escape of MA ions and the penetration of water into the perovskite absorber (Fig. 10c). The HS-PhF₅ modified device thereby showed enhanced water resistance, with no significant color change after 8 days and retaining almost 80% of its initial performance after 10 days of storage under ambient conditions with a relative humidity of 45%. Finally, the highest PCE of 14.1% was achieved for the modified PSCs.⁸⁷

Fig. 10 (a) Molecular structure of two isomers used for passivation for perovskite solar cells and their maximum power conversion efficiency. Reproduced with permission.⁸⁶ Copyright 2021, Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. (b) Schematic representation of defect passivation by 3-thenoic acid (TA 1), thiophene-3-acetic acid (TA 2), and 3-thiophenepropanoic acid (TA 3). Reproduced with permission.⁸⁵ Copyright 2021, the Royal Society of Chemistry. (c) Schematic representation of defect passivation by p-mercaptobenzoic acid and pentafluorobenzenethiol. Reproduced with permission.⁸⁷ Copyright 2015, the Royal Society of Chemistry. (d) Schematic representation of photocatalytic hydrogen evolution on bi-functionalized MHPs. Reproduced with permission.⁸⁸ Copyright 2024, Wiley-VCH GmbH.

Recently, Xu et al. introduced a very interesting strategy to improve photocatalytic hydrogen evolution using metal halide perovskites. In particular, MHPs were bi-functionalized with PbS and amorphous molybdenum sulfide (MoS_x) as co-catalysts.⁸⁸ The uncoordinated Pb²⁺ defects on the surface of MHPs were effectively passivated by PbS, thanks to the strong chemical interaction between Pb²⁺ and S²⁻ and thus increased charge transfer efficiency. Meanwhile, MoS_x can significantly promote the hydrogen evolution yield due to its high catalytic activity (Fig. 10d). Consequently, a maximum solar-to-chemical conversion efficiency of ca. 4.63% was achieved on the bi-functionalized FAPbBr_3−xI_x. Taking advantage of a strong Pb–S bond, Meng et al. demonstrated a passivation method by growing CsPbBr₃ quantum dots into a thiol-functionalized covalent-organic framework (COF-SH).⁸⁹ The strong interaction between the Pb atom in the perovskites and the S atom in COF-SH significantly reduced crystal defects and also prevented ion migration. Therefore, the CsPbBr₃@COF-SH composite showed much better thermal and air stability, as well as higher PLQY, compared to those of pristine CsPbBr₃. Moreover, CsPbBr₃@COF-SH was further used in photocatalytic systems with eosin Y (EY) and rose bengal (RB). The results indicate that ESY-CsPbBr₃@COF-SH and RB-CsPbBr₂I@COF-SH systems showed better performances in photocatalytic C–H selection and cross-coupling/annulation reactions, respectively, compared to ESY or RB alone.

2.2.4 Polymer passivators. Polymers are another typical class of effective passivators for MHP defects. Additionally, due to their long alkyl chains, the polymer passivators exhibit strong hydrophobicity and thus enhance the water resistance of perovskites. For example, Li et al. reported the introduction of an interfacial polystyrene (PS) layer between the perovskite film and spiro-OMeTAD layer.⁹⁰ The presence of the PS layer passivated the interface traps and defects. As a result, the PL intensity and carrier lifetime were significantly increased due to suppressed nonradiative recombination. In addition to defect passivation, the hydrophobic polymer chains form a protective interfacial barrier that limits moisture penetration and helps preserve the interfacial passivation structure during environmental exposure. The efficiency of PSCs incorporating polystyrene reached 20.46%. The passivated device retained almost 85% of its initial PCE after 60 days of storage under open-air conditions, which is 20% higher than that of the control device⁹⁰ (Fig. 11a). Contact angle measurements indicated that PS-modified perovskite films had higher water contact angles (approximately 92.5°) compared to pristine films (around 75.1°). Additionally, the PS-modified films exhibited a smaller reduction in contact angle over time, suggesting that the hydrophobic interfacial layer remained effective despite environmental exposure. Furthermore, after 2 months of storage, the PS-modified devices retained their black, opaque appearance, whereas the pristine devices showed significant signs of decomposition.

Fig. 11 (a) Normalized PCE of pristine and polystyrene-treated devices after the stability test in ambient air. Reproduced with permission.⁹⁰ Copyright 2018, American Chemical Society. (b) Schematic representation of perovskite solar cell devices with PEO and PS as the interfacial layers. Reproduced with permission.⁹¹ Copyright 2018, the Royal Society of Chemistry. (c) Infiltrative treatment process of perovskites with poly(vinylidene fluoride) (PVDF). Reproduced with permission.⁹² Copyright 2022, Wiley-VCH GmbH.

Similar to polystyrene, polyethylene oxide (PEO) can be inserted into the perovskite absorption layer and the charge extraction layer to passivate anion vacancies via the coordination of the C–O group with Pb ions⁹¹ (Fig. 11b). In addition, PEO can absorb water molecules, thereby hindering water penetration into the perovskite layer and significantly improving the moisture stability of PSCs (Fig. 11b). The PEO-treated device thereby retained 80% of its initial performance after 120 h of exposure to 88% humidity, while the untreated device showed continuous degradation of PCE from 15% to 1%. For the application of efficient perovskite LEDs, Feng et al. demonstrated an infiltrative treatment method for perovskites using poly(vinylidene fluoride) (PVDF), in which the polymer chains were added into the perovskite films before crystallization⁹² (Fig. 11c). The fluorine atoms in PVDF can interact with MA⁺/FA⁺ and Pb²⁺ ions via hydrogen and ionic bonds, passivating defects on the surfaces and along the GBs of perovskites. As a result, high-quality perovskite films were obtained, and the corresponding PeLEDs achieved an EQE of 22.29%, nearly 7.5% higher than that of the control device. The operating stability of PeLED devices was then measured, and the half-times of polymer-treated devices were nearly 7 times higher than those of the control device, indicating that PVDF significantly improved the stability of perovskite LEDs.⁹² Therefore, it can be inferred that the polymer-assisted passivation method was efficient for increasing the efficiency and stability of PeLEDs, and various polymer passivators were employed for this strategy, such as poly(methyl methacrylate) (PMMA),⁹³ poly(vinylpyrrolidone) (PVP),⁹⁴ and polyethylene glycol (PEG).⁹⁵

2.2.5 π-conjugated base passivators. π-Conjugated molecules are a class of molecules characterized by variable carbon hybridization, enabling the unrestricted movement of π-electrons within the system.⁹⁶ This feature enhanced the stability and electrical conductivity of π-conjugated molecules and their adducts.⁹⁶ Moreover, π-conjugated molecules can coordinate with lead atoms in perovskites via electron donors. Therefore, some π-conjugated materials can act as Lewis base passivators for perovskites, for example, indacenodithiophene end-capped with 1,1-dicyanomethylene-3-indanone (IDIC),⁹⁷ and with 4-bromo-7-dicyanovinyl-2,1,3-benzothiadiazole (SM2).⁹⁸ IDIC was introduced as an interlayer between the perovskite and the cathode. Fig. 12a showed that the O atom in the carbonyl group, the N atom in the cyano group, and the S atom in the thiophene group of IDIC could effectively passivate the Lewis acid traps (e.g., uncoordinated Pb²⁺ and Pb clusters) on the surface and at GBs of MAPbI₃ via formation of Lewis adducts. IDIC can promote electron extraction and transport from the perovskite layer due to its n-type semiconducting property. As a result, the MAPbI₃/IDIC-based solar cells achieved a high PCE of 19.5%, whereas the control device without IDIC achieved only 13.5%. Moreover, the introduction of IDIC enhanced the stability of PSCs when stored under a dry inert atmosphere, maintaining almost 90% of the initial PCE, which is better than the nearly 80% observed for devices without an IDIC layer.⁹⁷ On the other hand, SM2 molecules can be added to the perovskite precursor (Fig. 12b) and then passivate surface and GB defects via strong coordination of two cyano groups to uncoordinated Pb²⁺. It could also increase the charge separation and transport at the perovskite interface due to an appropriate alignment in the energy of its LUMO with the conduction band minimum (CBM) of the perovskite.⁹⁸ Thanks to these benefits, the PSCs treated with SM2 molecules achieved a high PCE of 21.2%.

Fig. 12 (a) Schematic representation of defect passivation in perovskites by forming Lewis adducts with IDIC. Reproduced with permission.⁹⁷ Copyright 2016, WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. (b) Synthesis of SM2 and treatment of perovskite with SM2 to passivate defects. Reproduced with permission.⁹⁸ Copyright 2020, WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Moreover, the hydrophobic nature of SM2 can retard the penetration of water molecules into the perovskite layer. Combined with defect passivation via Lewis acid–base interactions, this contributes to improved moisture stability of the perovskite solar cells. The SM2-treated device retained almost 80% of its initial PCE after 2000 h of storage at 25% RH, whereas the control device showed a significant loss, dropping to 61%.⁹⁸ The defect passivation at GBs by SM2 can also enhance the thermal stability of the perovskite since the grain boundaries can serve as channels for the rapid diffusion of atoms and ions, and they are vulnerable to thermal stress. While the control device degraded to 52% of its initial PCE after heating for 60 h at 80 °C, the one treated with SM2 remained at 71% of the original PCE.⁹⁸

2.2.6 Other Lewis base passivators. Beyond conventional Lewis bases passivators, graphene oxide (GO), oligomeric silica (OS), and graphitic carbon nitride (gC₃N₄) have also been identified as promising Lewis-base passivators for improving the structural and optical stability of metal halide perovskites.

The encapsulation of graphene oxide can not only mitigate surface defects but also improve the stability of MHPs by forming a protective shell, thereby enhancing their optical performance.⁹⁹ For example, the treatment of CsPbBr₃ with GO slightly increased the photocatalytic activity of MHPs in CO₂ reduction, with CO and CH₄ generation yields of 58.8 and 29.6 µmol g⁻¹, respectively, while the amounts of CO and CH₄ for reaction using pristine CsPbBr₃ were 49.5 and 22.9 µmol g⁻¹, respectively (Fig. 13a).¹⁰⁰

Fig. 13 (a) Schematic for photocatalytic CO₂ reduction by CsPbBr₃/GO quantum dots. Reproduced with permission.¹⁰⁰ Copyright 2017, American Chemical Society. (b) Schematic representation of forming an OS-wrapped perovskite thin film and the hypothesized perovskite-OS nanostructures. Reproduced with permission.¹⁰¹ Copyright 2019, American Chemical Society.

Bai et al. demonstrated a facile strategy to wrap perovskite grains with an oligomeric silica (OS) matrix, forming a core–shell structure.¹⁰¹ The –OCH₂CH₃ group in the OS layer can simultaneously passivate the defects at the surface and GBs of perovskites via a coordination bond of an oxygen atom with an uncoordinated Pb²⁺ ion (Fig. 13b). As a result, the trap density was significantly reduced, and the charge-carrier recombination lifetime was prolonged, thereby enhancing the PCE of MAPbI₃ PCs to 21.1%. Furthermore, the OS shell could serve as a physical barrier to prevent the penetration of external moisture and atmospheric gases. It might also inhibit internal ion migration and decomposition by blocking degradation pathways from internal and external sources in perovskite films. As a result, the moisture and operational stabilities of corresponding PSCs were dramatically improved. There was no impurity peak observed in the XRD pattern of the MAPbI₃@OS film after 60 days of exposure to the air, while the pattern of the pristine MAPbI₃ film showed the impurity peak for PbI₂ after exposure to air for 10 days. Moreover, the performance of the MAPbI₃ film drops rapidly due to degradation, whereas the MAPbI₃@OS film maintained almost 90% of its initial PCE after 1200 h.

Graphitic carbon nitride (gC₃N₄, GCN), which shares structural similarities with graphene, can also be used to passivate intrinsic defects and grain boundaries in perovskites. The Cs₂AgBiBr₆-GCN composites showed a reduced trap density due to defect passivation by GCN, resulting in a better photocurrent response compared to that of pristine Cs₂AgBiBr₆.¹⁰² In addition, GCN can serve as a supporting matrix and reduce the hydrophilicity of Cs₂AgBiBr₆, thereby increasing the moisture stability of the perovskites. In terms of photocatalysis, GCN already displayed high photoactivity,¹⁰² Cs₂AgBiBr₆-GCN composites exhibited 3 times and nearly 10 times higher CO and CH₄ production, respectively, compared to pure Cs₂AgBiBr₆ in photocatalytic CO₂ reduction.

2.2.7 Fullerene-based Lewis acid passivators. Fullerenes (C₆₀) and their derivatives are renowned for their high electron affinity and transport capability, which come from their distinctive spherical shape. They have been widely used as electron-transport layers and trap passivators in the design of perovskite solar cells.¹⁰³ Phenyl-C61-butyric acid methyl ester (PCBM) is the most representative fullerene derivative as a Lewis acid passivator. Huang et al. discovered that the deposition of PCBM onto the MAPbI₃ layer leads to a significant reduction in perovskite film trap-states by two orders of magnitude, accompanied by the suppression of photocurrent hysteresis (Fig. 14a).¹⁰⁴ The PCE of the PSC device with the PCBM layer increased by more than 200% to reach 14.9%. They also found that the high trap concentration can be attributed to the low thermal stability of perovskite materials, which decompose at the surface, and that eliminating photocurrent hysteresis can increase the stability of these devices. Niu et al. employed PCBM to passivate Pb–I antisite defects via the formation of a PCBM-halide radical.¹⁰⁵ The device with an MAPbI₃ film passivated with PCBM showed a maximum PCE of 18.41%, compared to 17.34% for the original device. The long-term stability of this perovskite film was also examined by exposure to ambient conditions (RH 50%) for 60 days without encapsulation. The perovskite film treated with PCBM remained unchanged, while the control film faded from black to yellow. Moreover, the PCBM passivated device retained 76% of its initial PCE after 40 days in the dark room, whereas the control device's PCE dropped to 64%. The passivated device also showed significant enhancement in thermal stability, with PCE remaining at almost 85% of the original value after heating at 80 °C for 24 h, compared to 55% for the control. This improvement in stability can be attributed to the combined effects of defect passivation at grain boundaries, strong molecular interactions with MAPbI3, and the enhanced hydrophobicity of the passivated film (Fig. 14b).¹⁰⁵ In 2017, Zhang and co-workers prepared an α-bis-PCBM-containing perovskite film, which exhibited a higher crystal quality and lower defect concentration.¹⁰⁶ The α-bis-PCBM network could passivate voids or pinholes that may form in the bulk active layer, thereby increasing the electron extraction efficiency of PSCs. The stability tests also showed that the α-bis-PCBM-containing perovskite-based device exhibited significant stability improvements, retaining 90.1% of its original PCE after 44 days under ambient conditions at 40% RH. On the other hand, under the same conditions, the PCE of the pristine control device and the PCBM-containing perovskite-based device decreased to 45.4% and 72.6% of their original values, respectively (Fig. 14c). The enhanced stability was further confirmed under additional stress conditions. The device showed minimal degradation of less than 10% after 44 days at 65 °C. Additionally, there was only a 4% drop in efficiency after 600 hours of continuous full-sun illumination with maximum power point tracking. This suggests that the passivation network derived from α-bis-PCBM remains stable even under prolonged environmental and operational stresses. By maintaining a compact microstructure with fewer pinholes and less prominent grain boundaries, the α-bis-PCBM network effectively provides interfacial protection. Moreover, the α-bis-PCBM-containing perovskite-based device showed higher thermal resistance at 85 °C than the other two corresponding devices. As a result, an excellent PCE of 20.8% for the α-bis-PCBM-containing device was obtained, compared to 19.9% for PCBM and 18.8% for the control device (Fig. 14d). Following that, in 2018, bis-PCBM mixed isomers, acting as Lewis acids, were added to the antisolvent, and N-(4-bromophenyl)thiourea (BrPh-ThR), acting as a Lewis base, was added to the perovskite precursor solution (Fig. 14e). Bis-PCBM can passivate the negatively charged defects by accepting an electron from PbI₃⁻ or uncoordinated halide ions, while BrPh-ThR can simultaneously passivate positively charged defects by binding with uncoordinated Pb²⁺ ions.¹⁰⁷ The synergistic effect of a Lewis base and a Lewis acid not only passivated the defects but also improved the perovskite grain size and increased charge-carrier separation and transport. As a result, the PCE of the corresponding perovskite solar cell device was improved to 21.7%. Moreover, introducing this Lewis acid and base increased the hydrophobicity of the perovskite film and improved its structural and interfacial properties, thereby enhancing moisture stability. After 30 days of exposure to an ambient environment of 45% relative humidity, the color of the perovskite film incorporated with bis-PCBM and BrPh-ThR remained persistent, whereas the control perovskite film almost faded to yellow. Cheng et al. employed the same strategy to simultaneously passivate positive and negative defects at the surface through the self-assembly of 4,4′-bipyridine (4,4′-BiPy) and 2,2′-bipyridine (2,2′-BiPy) as Lewis bases from PCBM (a Lewis acid) onto the perovskite layer.¹⁰⁸ By using 4,4′-BiPy, the trap density was reduced after the passivation, and the electron transport ability was also enhanced (Fig. 14f). Therefore, the CsPbI₂Br-based devices treated with PCBM:4,4′-BiPy showed greatly enhanced performance, increasing PCE from 10.74% to 12.09%. Compared to 4,4′-BiPy, the ligand 2,2′-BiPy can also passivate trap states, but it may cause phase transformation in perovskites; the PCE of devices treated with PCBM:2,2′-BiPy was lower.¹⁰⁸ Furthermore, the introduction of 4,4′-BiPy can improve the thermal stability of PSCs, showing that the all-inorganic PSC device containing 4,4′-BiPy retained 76% of its initial PCE after being heated for 52 h in air. In contrast, the all-inorganic PSC reference device retained only 51% of its original PCE after 41 h of heating.¹⁰⁸ Another derivative of fullerene, a Lewis-acid-featured fullerene skeleton after iodide ionization (PCBB-3N-3I, the structure is shown in Fig. 14g) was reported to effectively passivate the positively charged surface defects of perovskites via electrostatic interaction with iodide ions, resulting in an enhancement in PCE from 17.7% to 21.1%.¹⁰⁹ Furthermore, the reduction in surface defects also improved the ambient stability of the device treated with PCBB-3N-3I, which remained at 87% of its initial PCE after 150 h of storage under ambient conditions with RH of 40–50%. On the other hand, the device treated with PCBB-3N (the fullerene before iodide ionization, the structure is shown in Fig. 14g) displayed lower stability and a smaller PCE value because PCBB-3N exhibited less efficient defect passivation than PCBB-3N-3I.¹⁰⁹

Fig. 14 (a) Schematic representation of electron trap passivation by PCBM. Reproduced with permission.¹⁰⁴ Copyright 2014, Nature. (b) The prevention of MA loss and moisture attacks induced by PCBM. Reproduced with permission.¹⁰⁵ Copyright 2018, WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. (c) The PCE stability of the pristine, PCBM- and α-bis-PCBM perovskite solar cells in an ambient environment with 40% relative humidity. Reproduced with permission.¹⁰⁶ Copyright 2017, WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. (d) Maximum power conversion efficiency of the pristine, PCBM- and α-bis-PCBM perovskite solar cell devices. Reproduced with permission.¹⁰⁶ Copyright 2017, WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. (e) Schematic representation of the antisolvent process to incorporate bis-PCBM into perovskites. Reproduced with permission.¹⁰⁷ Copyright 2018, the Royal Society of Chemistry. (f) Schematic representation of defect passivation by 4,4′-BiPy and 2,2′-BiPy. Reproduced with permission.¹⁰⁸ Copyright 2019, International Solar Energy Society. (g) Structure of PCBB-3N and PCBB-3N-3I. Reproduced with permission.¹⁰⁹ Copyright 2019, The Author(s).

2.2.8 Fluorine-containing Lewis acid passivators. Due to their unique passivation mechanisms, many aromatic compounds containing fluorine atoms have gained considerable interest as Lewis acid passivators for perovskites. The strongly electronegative F-atoms can inductively withdraw electrons, making another atom in the molecule partially positively charged. This partially positively charged atom can passivate uncoordinated halogen ions and PbI₃⁻ antisite defects by accepting an electron from them. For example, Yang et al. designed a tris(pentafluorophenyl) phosphine (TPFP) agent as a surface passivator for perovskite solar cells.¹¹⁰ Due to the strong electron-withdrawing effect of 15 electronegative F atoms, the central phosphorus atom was positively charged, which can be used to heal halide defects at the surface (Fig. 15a). The positively charged phosphorus center can interact strongly with surface sites that lack halides, while the fluorinated aromatic groups create a highly hydrophobic interfacial environment. As a result, the recombination rate and phase segregation were reduced, leading to a significant enhancement in PCE to 22%. Moreover, the TPFP-treated perovskite solar cell device showed greater moisture resistance, retaining 63% of its initial PCE after 336 h at 75% RH, compared to just 21% for the control device. The slower optical and electrical degradation observed in the TPFP-treated films indicates that the passivation layer is sufficient to effectively suppress the formation of ion-migration pathways assisted by halide vacancies, even under humid conditions. This structural stability of the passivated surface is crucial, as moisture-induced degradation in mixed-halide perovskites is closely linked to the migration of halide and Cs ions, which can lead to irreversible phase segregation. Stronger hydrophobicity and defect passivation effects are responsible for the slower degradation rate of the TPFP-treated device. Abate et al. prepared a Lewis passivator, iodopentafluorobenzene (IPFB), to encapsulate the perovskite crystal (Fig. 15b).¹¹¹ In this molecule, F atoms with strong electronegativity can withdraw the electron from the aromatic ring due to inductive effects, leading to a decrease in the electron density of the iodine atom bonded to the ring. The iodine atom carries a partial positive charge, enabling it to engage in halogen bonding with electron-rich species such as halide anions (X⁻), forming a directional –C–I⋯X⁻ interaction. As a result, the uncoordinated halogen ions and Pb–X antisite defects were passivated, leading to slower recombination. Consequently, the IPFB-treated solar cells showed an increase in power conversion efficiency from 13% to more than 15.7%, and the efficiency stabilized at over 15% under a fixed 0.81 V forward bias. Another Lewis acid, 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ), exhibits the same passivation mechanism as IPFB molecules, in which the passivation group carries a partial positive charge due to the inductive electron-withdrawing effect of the F atoms. F4TCNQ was introduced as a dual-function interfacial layer that passivated the surface defects and was doped in the perovskite (Fig. 15c). As a result, the F4TCNQ-modified PSCs exhibited an excellent efficiency of 18.1% and improved long-term stability without encapsulation, retaining 60% of their initial PCE after 1000 h of storage in the ambient atmosphere.¹¹²

Fig. 15 (a) Schematic representation of TPFP-induced passivation and prevention of water contact. Reproduced with permission.¹¹⁰ Copyright 2020, WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. (b) Schematic representation of the binding of IPFB to supramolecular perovskites. Reproduced with permission.¹¹¹ Copyright 2014, American Chemical Society. (c) Schematic representation of a perovskite solar cell with F4TCNQ as an interfacial layer. Reproduced with permission.¹¹² Copyright 2016, the Royal Society of Chemistry.

3. Passivation of metal halide perovskites using metal cations

Metal cations with different valence states (monovalent, divalent, and trivalent) have been incorporated into perovskite systems to modulate defect chemistry and electronic properties. Depending on their oxidation state, ionic radius, and chemical environment, these cations may induce defect passivation, substitutional doping, alloying, or secondary-phase formation.^113–116 In the following sections, we discuss their roles according to valence classification.

3.1 Passivation by monovalent cations

Many alkali metal ions have been studied for passivating defects in perovskites. For instance, Na-passivated CsPbBr₃ nanocrystals can be synthesized by the ligand-assisted reprecipitation (LARP) method, in which NaBr and a precursor perovskite solution were mixed.¹¹⁷ Bromide anions can passivate the vacancies in perovskites, while Na⁺ cations prevent the migration of bromide ions from the surface of NCs by binding with them. As a result, the non-radiative recombination pathways were eliminated, and the passivated CsPbBr₃ NCs exhibited enhanced optical performance, achieving a PLQY of 66%. Furthermore, introducing Na⁺ improved the thermal and water stability of perovskite NCs. The PL intensity of passivated NCs retained 80% of the initial value after storing in water for 11 h, while the pristine NCs maintained only 20% of the original intensity (Fig. 16a). Na⁺ ions were reported to have a similar size to the MA⁺ organic cation in perovskite structures.¹¹⁸ Therefore, Na⁺ can be easily introduced into the A-site vacancy of a perovskite via doping to passivate the negatively charged defects, such as uncoordinated halogen ions. Zhang et al. successfully prepared perovskite solar cell devices with significant improvements in both efficiency and stability via surface modification with sodium p-toluenesulfonate (STS).¹¹⁹ The Na⁺ cation and sulfonate anion of STS can passivate the surface of the perovskite by interacting with uncoordinated Pb²⁺ and I⁻/Br⁻ ions, respectively. Consequently, the PCE of the STS-treated device increased to 20.05% compared to 18.7% for the non-passivated device (Fig. 16b). Moreover, the impact of STS passivation on the stability of the PSC device was investigated. The results revealed that the STS-treated device showed greater stability, with only 21% degradation in PCE after 950 h of exposure to an RH of 40–70%, compared to nearly 53% for the control device under the same conditions. This enhanced stability can be attributed to the hydrophobicity of the toluene group, which prevented the attacks of water and oxygen gas on the surface of perovskites.

Fig. 16 (a) Normalized PL intensity of pristine and Na-passivated CsPbBr3 NCs in deionized water. Reproduced with permission.¹¹⁷ Copyright 2021, Elsevier B.V. (b) Normalized PCE of PSC devices with and without STS modification stored under ambient conditions without encapsulation (temperature: 25 °C, relative humidity: 40–70%). Reproduced with permission.¹¹⁹ Copyright 2020, WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. (c) EQEs of PeLEDs fabricated from SDS-CsPbI₃ NCs and pure CsPbBr₃ NCs. Reproduced with permission.¹²⁰ Copyright 2021, American Chemical Society. (d) PLQE of perovskite thin films passivated with different fractions of potassium x. Reproduced with permission.¹²² Copyright 2018, Macmillan Publishers Limited, part of Springer Nature. (e) Long-term stability of passivated and non-passivated perovskite devices after more than 1000 hours under an average humidity of 10 ± 5%. Reproduced with permission.¹²³ Copyright 2017, the Royal Society of Chemistry. (f) H₂ evolution in experiments using K-MAPbBr₃/Mo₃S₁₃²⁻ and MAPbBr₃/Mo₃S₁₃²⁻ as photocatalysts. Reproduced with permission.¹²⁴ Copyright 2020, The Authors. EcoMat is published by John Wiley & Sons Australia, Ltd on behalf of The Hong Kong Polytechnic University. (g) PLQE of K- and Rb-passivated perovskite films with different fractions of additives. Reproduced with permission.¹²⁵ Copyright 2018, American Chemical Society. (h) The PCE of devices with and without Rb⁺ doping. Reproduced with permission.¹²⁶ Copyright 2019, WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. (i) PL intensity of undoped- and Rb-doped perovskites. Reproduced with permission.¹²⁷ Copyright 2022, WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The same surface passivation strategy was employed in another report, in which sodium dodecyl sulfate (SDS) was used to replace the traditional OA ligand.¹²⁰ SDS passivation significantly reduced trap density, thereby boosting the PLQY of SDS-CsPbI₃ NCs to nearly 100%. In addition, the incorporation of SDS significantly increased the stability of CsPbBr₃ NCs. The results showed that the red emission from pristine CsPbI₃ NCs disappeared after 20 min of water treatment. In comparison, the SDS-CsPbI₃ NCs retained over 70% of their original performance after 40 min under the same conditions. The SDS-CsPbI₃ NCs retained 40% of their initial PL intensity at high temperatures and showed no phase transformation under ambient conditions. On the other hand, the pristine CsPbI₃ NCs experienced a rapid reduction in PL intensity to zero at the same temperature. They transformed into the δ phase after exposure to ambient air for 5 days. DFT calculations revealed that improvements in both stability and photoluminescence can be attributed to the strong binding affinity of the SDS ligand, which preserves the perovskite surface. Consequently, the red PeLEDs fabricated from SDS-CsPbI₃ NCs showed superior color purity and performance, achieving a maximum EQE of 8.4%, compared to 2.1% for those using pristine CsPbI₃ NCs (Fig. 16c).

Son et al. reported a strong relationship between hysteresis and trap states generated by defects. As trap density decreased, hysteresis decreased gradually. Therefore, they proposed a strategy to synthesize hysteresis-free perovskite solar cells through defect passivation using alkali metal salts (LiI, NaI, KI, RbI, and CsI).¹²¹ The results showed that KI had the greatest effect on eliminating the hysteresis phenomenon. This can be attributed to the well-suited placement of K⁺ ions within the O_h interstitial site, preventing the migration of I ions. Consequently, the formation of iodide Frenkel defects, the primary contributors to hysteresis, was minimized. Removing hysteresis can improve the stability and optical performance of PCSs. As a result, an average PCE of 17.55% was obtained for KI-doped perovskite solar cells, compared with 17.14% for the pristine one. Adbi-Jalebi et al. employed a K⁺ passivator to prepare perovskite films with superior photoluminescence quantum efficiency (PLQE) and high photostability.¹²² With an appropriate amount of K⁺ doping, the PLQE reached 66%, corresponding to an internal yield of more than 95% (Fig. 16d). After passivation, the perovskite films showed very high photostability at the optimal bandgap under irradiation, while the pristine sample exhibited significant redshifts and changes in bandgap over time. Ion migration was also prevented, eliminating hysteresis. As a result, the PCE of the device based on passivated perovskites increased remarkably from 17.3% to 21.5%. Another study demonstrated a quadruple-cation perovskite K_xCs_0.05(FA_0.85MA_0.15)_0.95Pb(I_0.85Br_0.15)₃ in which the K⁺ ion showed self-passivation properties.¹²³ The passivation induced an improvement in the crystallinity and an increase in the grain size of the perovskite films. The trap states at GBs and interfaces were thus reduced, resulting in a slower recombination rate and longer carrier lifetime. Moreover, introducing the K⁺ cation significantly improved the long-term stability of the corresponding device, with no degradation in PCE after 1000 h under ambient conditions with RH of about 10 ± 5% (Fig. 16e). Consequently, a hysteresis-free, stable, and highly efficient PSC with a PCE of 20.56% was obtained. In the field of photocatalysis, the doping of the K⁺ cation into MAPbBr₃ to form K-MAPbBr₃ was revealed to efficiently prevent the formation of Pb⁰ and Br⁰ defects, and thus boosted the photostability of the perovskite in H₂ generation reaction.¹²⁴ After depositing the K-MAPbBr₃ with Mo₃S₁₃²⁻ nanoclusters, the amount of H₂ generated by K-MAPbBr₃/Mo₃S₁₃²⁻ significantly increased to nearly 80 µmol g⁻¹, which is 7.4 times higher than that of MAPbBr₃/Mo₃S₁₃²⁻ (Fig. 16f).

Compared with K⁺, the Rb⁺ ion shows a lower passivation capability. K⁺ and Rb⁺ were doped into triple cation perovskite (Cs_0.06MA_0.15FA_0.79)Pb(I_0.85Br_0.15)₃ to passivate the negatively charged defects, then the optical performance and chemical stability of the passivated perovskite films were examined.¹²⁵ The K-passivated films showed a significant increase in PLQE from 18% to 41%, while no change in PLQE was observed for the Rb-passivated ones. After exposure to an RH level of 50% for 24 h, the PLQE of K-passivated films increased to 49.2%, while the PLQE of Rb-passivated films dropped to 12.9% (Fig. 16g). These results suggested that potassium has a greater tolerance than rubidium. This is because, under high relative humidity conditions, both K- and Rb-passivated films degraded into non-perovskite phases. However, the Rb-rich phase had lower solubility and a negative effect on the film's photoluminescence, resulting in lower PLQE for Rb-passivated films. Nevertheless, Rb⁺ ions still have a specific passivation impact on perovskites. In particular, the Rb-doped CsPbI₂Br film had less recombination and lower defect density than the pristine one, which induced an increase in the PCE of the corresponding PSC device to reach a maximum value of 12% (ref. 126) (Fig. 16h). The air stability of PSCs based on the Rb-doped CsPbI₂Br film was also enhanced, in which more than 90% of the initial PCE was maintained after exposure to 20% humidity for 94 h. Meanwhile, the PCE of the device based on pristine CsPbI₂Br dropped to only 0.14% under the same conditions.¹²⁶ By adding an appropriate amount of RbI into the perovskite precursor solution, Rb-introduced (FAPbI₃)_0.85(MAPbBr₃)_0.15 perovskites with enhanced performance were fabricated.¹²⁷ In this case, Rb⁺ was reported to occupy the A-site and passivate the iodine vacancies in both grain interiors and grain boundaries. The electronic passivation effect of Rb resulted in significantly improved intrinsic photostability for the 5% Rb-introduced perovskites, exhibiting three times higher photoluminescence intensity (Fig. 16i) and a longer carrier lifetime compared to those of pristine perovskites. Furthermore, introducing Rb into perovskite materials can lead to the formation of Rb-containing secondary phases (e.g., RbPbI₃) at the surface, which modify interfacial energetics, as Rb was not incorporated into the main perovskite lattice.¹²⁸

The cesium ion has been widely used as a suitable cation to occupy the A-site in the perovskite structure. Inorganic cesium salts can be incorporated with perovskites to serve as surface passivators. Ling et al. reported that the post-treatment of CsPbI₃ quantum dots (QDs) with various inorganic cesium salts, including cesium acetate (CsAc), cesium iodide (CsI), cesium carbonate (Cs₂CO₃), and cesium nitrate (CsNO₃), can passivate the vacancies at the perovskite surface and prolong the carrier lifetime¹²⁹ (Fig. 17a). As a result, maximum PCEs of 14.10%, 13.14%, 13.74%, and 13.67% were obtained for CsAc-, Cs₂CO₃-, CsI-, and CsNO₃-treated CsPbI₃ QD solar cells, respectively, surpassing the control device which showed a PCE of 12.59%.

Fig. 17 (a) Schematic representation of the CsX post-treatment process to passivate the Cs vacancy. Reproduced with permission.¹²⁹ Copyright 2019, WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. (b) Long-term stability of CsPbI₂Br PSCs with and without CsBr treatment. All the devices were stored in N₂, while PCE was measured under ambient conditions. Reproduced with permission.¹³¹ Copyright 2019, WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. (c) The stability of the pristine and CsAc-treated PSCs in the dark under ambient conditions. Reproduced with permission.¹³⁰ Copyright 2019, WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. (d) Stability of the pristine and Cs-oleate PSC devices at room temperature under RH of 69%, without encapsulation. Reproduced with permission.¹³² Copyright 2019, American Chemical Society. (e) There is an increase in the EQE of PeLEDs after Ag⁺ passivation. Reproduced with permission.¹³⁴ Copyright 2018, American Chemical Society. (f) The PCE of the PSC device treated with NaI, CuI, and AgI. Reproduced with permission.¹³³ Copyright 2018, American Chemical Society. (g) The EQE of PeLED devices with different Ag⁺ doping concentrations. Reproduced with permission.¹³⁵ Copyright 2017, American Chemical Society.

Moreover, CsAc treatment could improve the stability of CsPbI₃ crystals. This effect should be attributed to cooperative ionic interactions in CsAc, where Ac⁻ coordinates with undercoordinated Pb²⁺ defects, while Cs⁺ contributes to lattice stabilization, thereby protecting the surface of perovskite QDs from moisture attack. The device based on CsAc-treated CsPbI₃ QDs retained 70% of its original PCE after storage for 54 h under a relative humidity of 40%, while the PCE of the control device dropped to 52% of its initial PCE under the same conditions.¹²⁹ Yuan et al. pointed out that incorporating CsAc into FA_0.85MA_0.15PbI₃ film reduced the defect density and improved the stability of perovskites due to the strong interaction of Ac⁻ with Pb²⁺ ions. The CsAc-treated PSCs exhibited an increase in maximum PCE from 19.47% to 21.95% and maintained 97% of their initial PCE after exposure for 55 days without encapsulation in air¹³⁰ (Fig. 17c). The passivation with CsBr positively impacted the performance and stability of CsPbI₂Br PSCs, where Br⁻ compensates halide vacancies, and Cs⁺ helps stabilize the perovskite lattice, resulting in an increased PCE from 11.8% to 16.3%. Additionally, the PCE of CsBr-passivated CsPbI₂Br PSCs only decreased to 86% of the initial value after storage for 1368 h in N₂. In contrast, the device without CsBr passivation retained only 57% of the initial PCE after 384 h under the same conditions¹³¹ (Fig. 17b). Guo et al. proposed a surface passivation strategy using cesium oleate (Cs-oleate), in which oleate anions coordinate with Pb²⁺ surface defects while Cs⁺ assists in structural stabilization. The device fabricated from Cs-oleate-treated perovskite films slightly improved the maximum PCE from 18.01% to 18.31%. Moreover, it retained 88% of its initial efficiency after 720 h of storage at room temperature under RH of 69%, without the use of any encapsulation.¹³² Besides alkali metal ions, monovalent metal cations such as Ag⁺ and Cu⁺ can be doped into the perovskite lattice since they have similar ionic radii as the Pb²⁺ ion,¹³³ leading to significant modification of the electronic structure. The Ag doped CsPbI₃ films showed enhanced stability against moisture and light irradiation, in which their PLQY retained 80% of the initial value after 48 h under ambient conditions. The LED device fabricated from Ag doped passivated CsPbI₃ films showed stronger PL intensity and a higher EQE of 11.2%, compared with the 7.3% of the non-passivated device¹³⁴ (Fig. 17e). Abdi-Jalebi et al. reported that the PLQE of Cu-doped CH₃NH₃PbI₃ films reached 12%, and the PCE of Cu-doped perovskite solar cells achieved a best value of 19.2% (ref. 133) (Fig. 17f). In addition, it should be noted that using an excess amount of Ag⁺ and Cu⁺ doping can result in a negative effect on the performance of perovskites; thus, in many cases, only low concentrations of Ag- and Cu-salts could be used.^133,135

3.2 Passivation by divalent metal cations

Divalent metal cations are typically doped into the perovskite lattice to replace the position of Pb²⁺ in the B-site. Many transition metals (e.g., Ni²⁺, Cu²⁺, Mn²⁺, Cd²⁺, and Zn²⁺) and alkaline earth metals (e.g., Mg²⁺, Ca²⁺, Sr²⁺) can be incorporated to effectively passivate negatively charged defects. For example, incorporating Ni²⁺ can reduce the trap density in the MAPbI₃ perovskite. This is because Ni²⁺ passivated PbI₃⁻ antisite defects and restrained the formation of Pb⁰ via interactions with uncoordinated halogen ions and halide-rich antisites¹³⁶ (Fig. 18a). The PSCs fabricated from 3% Ni²⁺-added MAPbI₃ films showed a significant increase in PCE, rising from 17.25% to 20.61%. The stability test also revealed that Ni²⁺ positively improved the air stability of the PSC device. The strong interaction of Ni²⁺ with I⁻ and MA⁺ not only affected the ordered arrangement of MA cations but also enhanced the crystallinity of the perovskite, consequently enhancing stability. Mn²⁺-doped perovskite NCs show a characteristic yellow-orange emission but have a very low PLQY due to a nonradiative recombination process at defect states. Co-doping with Mn²⁺ and Cu²⁺ can effectively passivate these trap states. Therefore, the Cu²⁺–Mn²⁺-codoped CsPbCl₃ NCs showed significantly enhanced photoluminescence performance to reach a best PLQY of 80% (Fig. 18b), compared to only 11% for that of Mn²⁺-doped NCs.¹³⁷ Moreover, Cu²⁺ exhibits better thermal stability, potentially improving the stability of perovskite NCs. Cd²⁺ is reported in many publications as an efficient ionic dopant for defect passivation in perovskites. Zhao et al. presented an interfacial passivation method for synthesizing high-efficiency, stable PSCs by incorporating CdS into perovskite layers. Cd²⁺ cations can passivate iodide vacancy defects by forming a strong Cd–I bond. At the same time, S²⁻ anions simultaneously fill the iodide vacancy, reducing the trap density in perovskites and improving charge transport ability. As a result, the PSC device based on CdS-treated perovskites achieved an excellent PCE of 21.62%, compared to the 19.97% PCE of the control device. Additionally, the long-term stability of the device was improved after the introduction of CdS, with CdS-modified PSCs retaining 87.5% of the initial efficiency after storage in N₂ for 410 h. In comparison, the control device showed a 30% drop in its initial PCE under the same conditions¹³⁸ (Fig. 18c). The surface passivation with CdI₂ can yield perovskite solar cells with even higher efficiency and stability.

Fig. 18 (a) Schematic for defect passivation in MAPbI₃ by Ni²⁺ ions.¹³⁶ Copyright 2018, WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. (b) The PLQY of Mn²⁺-doped CsPbI₃ NCs before and after treatment with CuCl₂. Reproduced with permission.¹³⁷ Copyright 2021, American Chemical Society. (c) Stability of the control and CdS-treated devices under a N₂ atmosphere. Reproduced with permission.¹³⁸ Copyright 2021, American Chemical Society. (d) Stability of the control and CdI₂-treated PSCs under continuous 1 sun illumination with encapsulation. Reproduced with permission.¹³⁹ Copyright 2022, American Chemical Society. (e) Schematic representation of defect passivation in perovskites by Cd²⁺ and the PCE after further treatment with KCl. Reproduced with permission.¹⁴⁰ Copyright 2021, American Chemical Society. (f) The photostability of unencapsulated devices with different contents of Zn under extended light illumination at 100 mW cm⁻² in a N₂ glovebox. Reproduced with permission.¹⁴¹ Copyright 2020, AIP. (g) Stability of the Ca²⁺-doped CsPbI₃ NC solutions under daylight before and after 147 days of storage (from left to right: Ca/Pb = 0%, 0.35%, 0.40%, 1.20%). Reproduced with permission.¹⁴⁴ Copyright 2021, Wei Shen et al. Exclusive Licensee Science and Technology Review Publishing House. (h) The EQEs of PeLEDs at different Ca/Pb ratios. Reproduced with permission.¹⁴⁴ Copyright 2021, Wei Shen et al. Exclusive Licensee Science and Technology Review Publishing House. (i) The stability of the pristine and Mg²⁺-treated CsPbI₃ NCs in solution after 80 days. Reproduced with permission.¹⁴³ Copyright 2021, American Chemical Society. (j) The PLQY and violet emission of a Ca²⁺-doped perovskite solution. Reproduced with permission.¹⁴⁵ Copyright 2019, American Chemical Society.

Wu et al. reported that CdI₂-treated PSCs exhibited a PCE of 21.9% with improved operational stability, maintaining 92% of the initial efficiency after 1000 h under continuous irradiation at 1 sun intensity¹³⁹ (Fig. 18d). By monitoring the content of the CdI₂ additive, Ji et al. obtained a champion PSC device with a very high PCE of 21.95% at 0.5% Cd²⁺-doping. Moreover, this device showed good long-term stability, wherein its PCE degraded only 12% after exposure for 42 days in ambient air with a RH of 50%. On the other hand, the PCE of the control device experienced about 17% loss under the same conditions.¹⁴⁰ The efficiency of Cd²⁺-incorporated perovskite solar cells can be further boosted to 22.75% by additional interfacial passivation by KCl¹⁴⁰ (Fig. 18e). Zn²⁺ has been found to aggregate at grain boundaries when a high concentration of ZnI₂ was added to the perovskite precursor.¹⁴¹ This aggregation of Zn²⁺ can heal the defect at GBs, leading to a reduction in non-radiative recombination. Furthermore, the formation of the non-perovskite phase and PbI₂ precipitate was minimized after introducing the Zn ion. As a result, the device based on Zn²⁺-doped PSCs showed an improved overall performance and higher stability, resulting in an increased power conversion efficiency from 18.4% (for the control device) to 20.7%, with only a 5% loss of the initial PCE after continuous illumination for 300 h (ref. 141) (Fig. 18f). Another halide salt of zinc, ZnBr₂, was used to passivate the surface defects of CsPbBr₃, as it allowed Br⁻ to fill the vacancy on the surface.¹⁴² Moreover, Zn²⁺ ions were revealed to act as catalytic sites for CO₂ reduction. As a result, the ZnBr₂–CsPbBr₃ showed approximately three times higher CO formation yield than that of pure CsPbBr₃ in photocatalytic CO₂ reduction. Chen et al. employed a hot-injection method to synthesize Mg²⁺-treated CsPbI₃ NCs. They discovered that Mg²⁺ ions were not incorporated to replace Pb²⁺ but mainly dispersed on the surface of perovskite NCs and then passivated the defects in this region. The non-radiative recombination pathways were thereby reduced, increasing the PLQY of the as-prepared Mg–CsPbI₃ NCs from 77% to 95%.¹⁴³ Following surface passivation with Mg²⁺, the optical and structural stability of perovskite NCs were improved. As shown in Fig. 18i, the Mg–CsPbI₃ NCs maintained over 80% of their initial PLQY after storage in air for 80 days and showed no obvious color change or phase transformation after 9 days. The improved stability can primarily be attributed to Mg²⁺-derived surface species on nanocrystals. These species effectively passivate surface defects and partially isolate the nanocrystals from their external environment. The fact that the cubic phase remains evident in the XRD results even after 9 days suggests that the surface passivation structure stays sufficiently stable during aging. This stability helps prevent surface reconstruction and moisture-induced phase transitions. Consequently, a high-efficiency, stable red LED device based on Mg–CsPbI₃ NCs was successfully fabricated, demonstrating an external quantum efficiency of 8.4%, four times that of the pristine CsPbI₃ LED. Ca²⁺ doping has been reported as a powerful method to boost the optical performance and stability of perovskite films. Ca²⁺-doped CsPbI₃ NCs showed a maximum PLQY of 93%, 4% higher than that of the undoped ones. Moreover, Ca²⁺-doped CsPbI₃ NCs can retain up to 83% of their initial PL intensity after storage for 147 days under 20 ± 5 °C and 40–50% RH (Fig. 18g). The improved long-term stability is linked to the preservation of the nanocrystal surface and crystal structure upon Ca²⁺ incorporation. In contrast to pristine CsPbI₃ NCs, which became nonuniform, aggregated, and lost their cubic shape during storage, the Ca²⁺-doped nanocrystals maintained a uniform cubic form and exhibited stable red emission. In solid films, Ca²⁺-doped CsPbI₃ retained the cubic α-phase after 58 days under ambient conditions, while the undoped films gradually transitioned to the orthorhombic δ-phase. These findings indicate that Ca²⁺ incorporation stabilizes the local lattice environment and reduces structural changes induced by ion migration, thereby preserving the passivated structure under prolonged ambient and thermal stress. As a result, the red LED fabricated from Ca²⁺-doped CsPbI₃ NCs demonstrated a nearly three-fold increase in maximum EQE to 7.8% (ref. 144) (Fig. 18h). These improvements were primarily attributed to the beneficial impact of Ca²⁺ doping, which led to a reduction in defect density and a lower hole injection barrier in perovskite films. The incorporation of Ca²⁺ can yield perovskite NCs with high efficiency and unique violet emission (Fig. 18j). However, the stability of Ca²⁺-doped NCs was not discussed in this case.¹⁴⁵ The ionic radius of Sr²⁺ (1.18 Å) is almost the same as that of Pb²⁺ (1.19 Å). Therefore, Sr²⁺ is very suitable for doping into a perovskite to replace Pb²⁺. Many publications on employing Sr²⁺ doping to synthesize perovskite films with high PLQY and improved stability have been reported.^146–148 The red PeLEDs based on CsPbI₃ : 1.8% Sr²⁺ showed high stability under ambient conditions and demonstrated a maximum EQE of 17.1%, a world record at the time. On the other hand, Ba²⁺ has a much larger ionic radius (1.35 Å) than Pb²⁺ ions.¹⁴⁵ Therefore, the introduction of Ba²⁺ to replace Pb²⁺ can generate more defects in the perovskite lattice. Consequently, Ba²⁺-doped perovskite NCs showed extremely poor PLQY when compared to other alkaline earth metal-doped NCs.¹⁴⁵

3.3 Passivation by trivalent metal ions

Despite the mismatch in oxidation states with Pb²⁺, some trivalent metal ions still have the potential to be doped into the perovskite lattice, such as group III metals (Al³⁺, In³⁺),^149,150 group V metals (Bi³⁺, Sb³⁺),^151,152 and lanthanide metals (Sm³⁺, Yb³⁺).^153,154

Al–Br and Pb–Br bonds have shown similar dissociation energy, thereby Al³⁺ can be easily incorporated into the perovskite lattice.¹⁵⁵ In 2016, Wang et al. reported that Al³⁺ doping can reduce the electronic defect density and thereby improve the PLQE of perovskite films from 15% to 35% (Fig. 19a). The PSCs based on Al³⁺-doped films achieved a maximum PCE of 19.1% and a stabilized power output of 18.2%.¹⁵⁶ Subsequently, Yang et al. proposed a strategy using aluminum(III) acetylacetonate (Al(acac)₃) for doping Al³⁺ into CsPbBr₃ QDs.¹⁴⁹ The incorporation of Al³⁺ facilitated the Cl⁻ anion-exchange process to afford stable mixed Br/Cl perovskite QDs with deep-blue emission.¹⁴⁹ The results showed that Al³⁺ doping significantly reduced defects in the as-prepared CsPb(Br/Cl)₃:Al QDs, leading to an increased radiative recombination ratio and an extended average lifetime. In addition, the Al-doped QDs exhibited remarkable moisture stability, with negligible phase degradation and spectral shifts after storage in water for 240 h. Consequently, a deep-blue LED was fabricated from CsPb(Br/Cl)₃:Al QDs, demonstrating good spectral stability and a maximum EQE of 1.38%, exceeding that of an LED device based on pristine perovskite QDs (Fig. 19b). Recently, indium has been widely used to synthesize lead-free perovskites mainly due to its non-toxic nature.^157,158 Therefore, In³⁺ is a potential candidate for replacing Pb²⁺ in the perovskite lattice. By controlling the dopant concentration, Zhu et al. successfully prepared an In-doped perovskite sample with enhanced crystallinity and less boundary defects at the 4% InBr₃ additive.¹⁵⁰ The PSCs based on CsPbI_2.5Br_0.5-4%-InBr₃ films exhibited a remarkably enhanced PCE of 12.05%, compared to a PCE of 7.5% for those based on undoped films. Furthermore, the CsPbI_2.5Br_0.5-4%-InBr₃-based PSCs displayed superior thermal resistance, in which their PCE maintained 80% of the initial value after being heated for more than 1600 h at 100 °C (Fig. 19c). On the other hand, the PSCs based on pristine CsPbI_2.5Br_0.5 only retained 50% of the initial PCE after 800 h at the same temperature.¹⁵⁰ Zhou et al. obtained high-efficiency and stable indium-doped perovskite quantum dots (PeQDs) at 10% In³⁺ dopant¹⁵⁸ using the same concentration-controlled strategy. The 10% In³⁺-doped CsPbBr_xI_3−x PeQDs displayed an impressive near-unity PLQY of 99.8% and extremely high stability. These PeQDs retained over 70% of their initial PLQY after storage in n-hexane for more than six months under ambient conditions, with no considerable change in red emission color. These improvements in photoluminescence and stability can mainly be attributed to the effective passivation of surface vacancy defects induced by In³⁺ doping. Benefiting from these enhancements, the pure red PeLED based on 10% In³⁺-doped CsPbBr_xI_3−x PeQDs displayed an increased maximum EQE of 11.2% and higher stability than that of the pristine PeLED.¹⁵⁹

Fig. 19 (a) The PLQEs of the control and Al³⁺-doped perovskite films as a function of excitation power. Reproduced with permission.¹⁵⁶ Copyright 2016, the Royal Society of Chemistry. (b) The EQE of CsPb(Br/Cl)₃:Al QDs (ACPBC) and CsPb(Br/Cl)₃ QDs (MCPBC) as a function of current density. Reproduced with permission.¹⁴⁹ Copyright 2023, the Royal Society of Chemistry. (c) Thermal stability of the pristine and InBr₃-treated PSCs under heating at 100 °C. Reproduced with permission.¹⁵⁰ Copyright 2023, American Chemical Society. (d) EQEs of the pristine and In³⁺-doped PeLEDs. Reproduced with permission.¹⁵⁹ Copyright 2021, Wiley-VCH GmbH. (e) PCE of Eu³⁺-doped PSCs. Reproduced with permission.¹⁶⁵ Copyright 2019, Science. (f) Stability of Eu³⁺-doped PSCs. Reproduced with permission.¹⁶⁵ Copyright 2019, Science.

Bi³⁺ doping has attracted significant interest among trivalent metal cations because of its similar electron configuration to that of Pb²⁺ ions (6s²6p⁰).¹⁶⁰ Incorporating Bi³⁺ can afford perovskite materials with a narrow bandgap and near-infrared (NIR) luminescence.^161,162 However, Bi³⁺ doping was also reported to increase the structural defects in perovskites.¹⁶³ Therefore, the Bi³⁺ ion cannot be used as a perovskite passivator. Similarly, introducing Sb³⁺ might induce some defects (e.g., Pb vacancies), thus reducing the electron mobility in perovskite materials.¹⁶⁴ Incorporating lanthanide ions into the perovskite lattice can provide many benefits in photoluminescence performance and improve the stability of materials. For example, a 3% Sm³⁺-doped CsPbBr₃-based PSC device can retain more than 90% of the initial PCE after 60 days at 80 °C and 0% humidity, while the PCE of undoped PSCs dropped to 80% of the initial value under the same conditions.¹⁵³ Yb³⁺-doped CsPbCl₃ NCs exhibited NIR emission with an outstanding PLQY of approximately 200% due to the quantum cutting phenomenon.¹⁵⁴ However, a limited number of publications have considered the passivation effects of lanthanide ions on lead halide perovskites. Wang et al. demonstrated that Eu³⁺ doping can simultaneously eliminate the Pb⁰ and I⁰ defects in the perovskite lattice. This occurred because Eu³⁺ initially oxidized Pb⁰, generating Eu²⁺, which then reduced I⁰. After passivation, the Eu³⁺-doped device displayed an increase in maximum PCE to 21.52% (Fig. 19e) and long-term stability¹⁶⁵ (Fig. 19f).

4. Conclusion and outlook

In conclusion, organic ions, organic Lewis acids and bases, and metal cations have all demonstrated the ability to passivate various defect types in metal halide perovskites. Various organic ions can heal negatively charged defects by forming ionic bonds. While Lewis bases can passivate positively charged defects at perovskite surfaces and GBs by electron donation, Lewis acids can accept electrons to passivate negatively charged defects, such as uncoordinated halogen and Pb–X antisite defects. In addition, metal cations with different covalent bonds can be doped into the perovskite lattice, thereby passivating surface or grain-boundary defects. The positive influence of defect passivation is evident in the enhanced performance and stability of perovskite-based devices. Consequently, the passivated perovskite solar cells and perovskite light-emitting diodes exhibit significantly improved power conversion efficiency and external quantum efficiency, respectively, along with enhanced thermal and moisture stability.

However, there are a few reports on boosting the photocatalytic activity of metal halide perovskites through defect passivation (summarized in Table 1). The key points for a semiconductor to become a good photocatalyst are strong absorption of visible light, efficient charge generation and transfer, abundant active sites and large surface areas, and high thermal and optical stability.¹⁶⁶ Defects in the semiconductor can affect all these features, offering both advantages and disadvantages. Therefore, further experimental and theoretical studies are needed to develop novel passivation strategies to improve the photocatalytic performance of perovskite catalysts.

Table 1 Summary of the performance of passivated perovskites in photocatalysis

Photocatalyst	Defect type	Passivator	Catalyzed reaction	Performance	Year	Ref.
CsPbBr3–SOBr2	Surface defects	SOBr2	CO2 reduction	Total CO and CH4 production rate: 190 µmol g^−1 h^−1	2022	60
CsPbBr3–SOBr2/g-C3N4	Surface defects	SOBr2	CO2 reduction	CO2 photoreduction yield of 190 µmol g^−1 h^−1	2022	60
CsPbBr3–BF4/Co^2+	Surface defects	BF^4−	CO2 reduction	Total CO and CH4 evolution rate of 83.8 µmol g^−1 h^−1	2021	58
MoSx/S-FAPbBr3−xIx	Uncoordinated Pb^2+	S^2−	H2 generation	Solar-to-chemical (STC) conversion efficiency of ca. 4.63%	2024	88
K-MAPbBr3/Mo3S13^2−	Pb^0 and Br^0 defects	K^+	H2 generation	H2 generation yield of 80 µmol g^−1, which is 7.4 times higher than that of MAPbBr3/Mo3S13^2−	2020	124
ZnBr2–CsPbBr3	Br vacancies	Br^−	CO2 reduction	The yield is three times higher than that of pristine CsPbBr3	2024	142
ESY-CsPbBr3@COF-SH	Surface defects	COF-SH	C–H selenization	Yield up to 99.3%	2021	89
(DETA)BiBr6/Cs2AgBiBr6	Br defects	DETA	Toluene oxidation	Up to 100%	2023	67
RB-CsPbBr2I@COF-SH	Surface defects	COF-SH	Cross-coupling/annulation	Yield up to 95.5%	2021	89
Cs2AgBiBr6-GCN	Intrinsic defects and grain boundaries	GCN	CO2 reduction	12.14 µmol g^−1 h^−1 of CO and 8.85 µmol g^−1 h^−1 of CH4 generated	2023	102

---

In this context, distinguishing between intrinsic and extrinsic degradation mechanisms is crucial for developing effective stabilization strategies. Intrinsic instability originates from material-inherent processes such as ion migration, phase segregation, and defect evolution, whereas extrinsic instability is driven by environmental stressors including moisture, oxygen, and thermal stress. Future passivation approaches should be tailored to address both classes of degradation. While extrinsic pathways are often mitigated through encapsulation or surface protection, intrinsic degradation requires targeted passivation of defects and interfaces. In this context, multi-functional passivators that combine defect binding with environmental barrier properties represent a promising route to simultaneously suppressing multiple degradation pathways and enhancing long-term stability.

Defect passivation can tune the bandgap to match the energy requirements for specific photocatalytic reactions, such as CO₂ reduction. Morphology modification, which specifically alters the perovskite phase beyond the conventional cubic phase, can be a viable and promising approach, since it can provide more active sites for the catalysis. 2D/3D mixed perovskites have been widely reported to enhance the performance of perovskite LEDs,¹⁶⁷ so the preparation of 2D/3D perovskite materials can become another effective passivation method. In these systems, the 2D layer can act as a protective barrier that passivates surface defects and inhibits ion migration, while the 3D layer with a higher surface area is responsible for catalysis. Replacing the Pb²⁺ ion in traditional halide perovskites with other metal ions, such as Sn²⁺ or In²⁺, might prevent defect formation during synthesis and reduce the environmental toxicity of Pb. Defect passivation with a co-catalyst can significantly increase the catalytic activity of the materials by leveraging the synergy between the perovskite and the co-catalyst. Interfacial passivation would be essential at the perovskite/co-catalyst interfaces, particularly with optimal charge-transport layers, where significant non-radiative recombination and instability can occur. While conventional approaches often focus on single interfaces, emerging strategies such as graded passivation, bilayer architectures, and deliberate interface engineering aim to simultaneously suppress interfacial defects and enhance charge extraction. These approaches are expected to play a central role in reducing interfacial losses while improving both device efficiency and long-term stability. Moreover, this approach offers the opportunity to make perovskites active in new catalytic reactions beyond CO₂ reduction and H₂ generation.

In addition, operational stability under realistic conditions must be established. Stability should be assessed under practical operating conditions, including continuous illumination, electrical bias, elevated temperature, and humidity, to accurately evaluate passivation strategies. The adoption of standardized testing protocols that combine multiple stress factors would enable more meaningful comparison of passivation efficacy across studies and accelerate the translation of laboratory advances into reliable devices. For instance, advanced in situ and operando characterization techniques, such as photoluminescence, X-ray diffraction, and transmission electron microscopy, are crucial for tracking defect evolution and interfacial changes under operating conditions. These approaches can provide direct insight into dynamic passivation mechanisms that are inaccessible to ex situ measurements. In parallel, DFT calculations and machine learning approaches offer powerful tools to predict effective passivators and unravel structure–property relationships at the atomic scale, enabling more rational and accelerated passivation design.

Conflicts of interest

There are no conflicts to declare.

Data availability

No data availability statement is required for the review.

Acknowledgements

T. H. Hoang acknowledges her PhD funding from the France Exellence program. The authors gratefully acknowledge funding from the European Union's Horizon Europe research and innovation program for the SUNPEROM project (Grant Agreement No. 101223212). M. N. GHAZZAL acknowledges funding from the ERA.NET” title = "http://M-ERA.NET">M-ERA.NET joint Call 2023 for the project with Reference Number: project11468. M. Abdi-Jalebi acknowledges University College London's Research, Innovation and Global Engagement, UCL – Korea University Strategic Partner Fund, for financial support.

References

1. Y. Fu, H. Zhu, J. Chen, M. P. Hautzinger, X.-Y. Zhu and S. Jin, Metal Halide Perovskite Nanostructures for Optoelectronic Applications and the Study of Physical Properties, Nat. Rev. Mater., 2019, 4(3), 169–188,  DOI:10.1038/s41578-019-0080-9.
2. M. Knezevic, T.-H. Hoang, N. Rashid, M. Abdi-Jalebi, C. Colbeau-Justin and M. N. Ghazzal, Recent Development in Metal Halide Perovskites Synthesis to Improve Their Charge-Carrier Mobility and Photocatalytic Efficiency, Sci. China Mater., 2023, 66(7), 2545–2572,  DOI:10.1007/s40843-023-2469-4.
3. Y. Miyazawa, M. Ikegami, H.-W. Chen, T. Ohshima, M. Imaizumi, K. Hirose and T. Miyasaka, Tolerance of Perovskite Solar Cell to High-Energy Particle Irradiations in Space Environment, iScience, 2018, 2, 148–155,  DOI:10.1016/j.isci.2018.03.020.
4. P. Ramasamy, D.-H. Lim, B. Kim, S.-H. Lee, M.-S. Lee and J.-S. Lee, All-Inorganic Cesium Lead Halide Perovskite Nanocrystals for Photodetector Applications, Chem. Commun., 2016, 52(10), 2067–2070,  10.1039/C5CC08643D.
5. J. Shamsi, A. S. Urban, M. Imran, L. De Trizio and L. Manna, Metal Halide Perovskite Nanocrystals: Synthesis, Post-Synthesis Modifications, and Their Optical Properties, Chem. Rev., 2019, 119(5), 3296–3348,  DOI:10.1021/acs.chemrev.8b00644.
6. M. Cao, Y. Damji, C. Zhang, L. Wu, Q. Zhong, P. Li, D. Yang, Y. Xu and Q. Zhang, Low-Dimensional-Networked Cesium Lead Halide Perovskites: Properties, Fabrication, and Applications, Small Methods, 2020, 4(12), 2000303,  DOI:10.1002/smtd.202000303.
7. Y. Lei, Y. Xu, M. Wang, G. Zhu and Z. Jin, Origin, Influence, and Countermeasures of Defects in Perovskite Solar Cells, Small, 2021, 17(26), 2005495,  DOI:10.1002/smll.202005495.
8. 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,  DOI:10.1021/ja809598r.
9. J. J. Yoo, G. Seo, M. R. Chua, T. G. Park, Y. Lu, F. Rotermund, Y.-K. Kim, C. S. Moon, N. J. Jeon, J.-P. Correa-Baena, V. Bulović, S. S. Shin, M. G. Bawendi and J. Seo, Efficient Perovskite Solar Cells via Improved Carrier Management, Nature, 2021, 590(7847), 587–593,  DOI:10.1038/s41586-021-03285-w.
10. M. Tao, Y. Wang, K. Zhang, Z. Song, Y. Lan, H. Guo, L. Guo, X. Zhang, J. Wei, D. Cao and Y. Song, Molecule-Triggered Strain Regulation and Interfacial Passivation for Efficient Inverted Perovskite Solar Cells, Joule, 2024, 8(11), 3142–3152,  DOI:10.1016/j.joule.2024.08.003.
11. Z. Su, M. Cui, B. Dong, Y. Zhang, Y. Ran, G. Qi, Y. Yang, T. Edvinsson, A. Hagfeldt, L. Jiang, Q. Fan, W. Ma and Y. Liu, Stereo-Hindrance Induced Conformal Self-Assembled Monolayer for High Efficiency Inverted Perovskite Solar Cells, Small, 2024, 20(52), 2407387,  DOI:10.1002/smll.202407387.
12. Y. Yang, H. Chen, C. Liu, J. Xu, C. Huang, C. D. Malliakas, H. Wan, A. S. R. Bati, Z. Wang, R. P. Reynolds, I. W. Gilley, S. Kitade, T. E. Wiggins, S. Zeiske, S. Suragtkhuu, M. Batmunkh, L. X. Chen, B. Chen, M. G. Kanatzidis and E. H. Sargent, Amidination of Ligands for Chemical and Field-Effect Passivation Stabilizes Perovskite Solar Cells, Science, 2024, 386(6724), 898–902,  DOI:10.1126/science.adr2091.
13. Y. Li, Z. Xie, Y. Duan, Y. Li, Y. Sun, C. Su, H. Li, R. Sun, M. Cheng, H. Wang, D. Xu, K. Zhang, Y. Wang, H. Lei, Q. Peng, K. Guo, S. Liu and Z. Liu, Successive Reactions of Trimethylgermanium Chloride to Achieve > 26% Efficiency MA-Free Perovskite Solar Cell With 3000-Hour Unattenuated Operation, Adv. Mater., 2025, 37(7), 2414354,  DOI:10.1002/adma.202414354.
14. L. Kazmerski, Best Research Cell Efficiencies Chart, Natl. Renew. Energy Lab. NREL, 2012, https://www.nlr.gov/pv/cell-efficiency.
15. C. Ma and N.-G. Park, A Realistic Methodology for 30% Efficient Perovskite Solar Cells, Chem, 2020, 6(6), 1254–1264,  DOI:10.1016/j.chempr.2020.04.013.
16. T. J. Milstein, D. M. Kroupa and D. R. Gamelin, Picosecond Quantum Cutting Generates Photoluminescence Quantum Yields Over 100% in Ytterbium-Doped CsPbCl₃ Nanocrystals, Nano Lett., 2018, 18(6), 3792–3799,  DOI:10.1021/acs.nanolett.8b01066.
17. M. Lu, Y. Zhang, S. Wang, J. Guo, W. W. Yu and A. L. Rogach, Metal Halide Perovskite Light-Emitting Devices: Promising Technology for Next-Generation Displays, Adv. Funct. Mater., 2019, 29(30), 1902008,  DOI:10.1002/adfm.201902008.
18. X.-K. Liu, W. Xu, S. Bai, Y. Jin, J. Wang, R. H. Friend and F. Gao, Metal Halide Perovskites for Light-Emitting Diodes, Nat. Mater., 2021, 20(1), 10–21,  DOI:10.1038/s41563-020-0784-7.
19. Z.-K. Tan, R. S. Moghaddam, M. L. Lai, P. Docampo, R. Higler, F. Deschler, M. Price, A. Sadhanala, L. M. Pazos, D. Credgington, F. Hanusch, T. Bein, H. J. Snaith and R. H. Friend, Bright Light-Emitting Diodes Based on Organometal Halide Perovskite, Nat. Nanotechnol., 2014, 9(9), 687–692,  DOI:10.1038/nnano.2014.149.
20. Z. Chu, Q. Ye, Y. Zhao, F. Ma, Z. Yin, X. Zhang and J. You, Perovskite Light-Emitting Diodes with External Quantum Efficiency Exceeding 22% via Small-Molecule Passivation, Adv. Mater., 2021, 33(18), 2007169,  DOI:10.1002/adma.202007169.
21. Z. Wang, C. Hong Mak, J. Feng, H.-H. Shen, B. Han, S. Permatasari Santoso, M. Yuan, F.-F. Li, H. Song, D.-J. Lee, J. Carlos Colmenares and H.-Y. Hsu, Nanoscale Halide Perovskites for Photocatalytic CO₂ Reduction: Product Selectivity, Strategies Implemented, and Charge-Carrier Separation, J. Mater. Chem. A, 2024, 12(32), 20542–20577,  10.1039/D4TA02446J.
22. J. Sun, J. Yang, J. I. Lee, J. H. Cho and M. S. Kang, Lead-Free Perovskite Nanocrystals for Light-Emitting Devices, J. Phys. Chem. Lett., 2018, 9(7), 1573–1583,  DOI:10.1021/acs.jpclett.8b00301.
23. J. Luo, M. Hu, G. Niu and J. Tang, Lead-Free Halide Perovskites and Perovskite Variants as Phosphors toward Light-Emitting Applications, ACS Appl. Mater. Interfaces, 2019, 11(35), 31575–31584,  DOI:10.1021/acsami.9b08407.
24. L.-Z. Lei, Z.-F. Shi, Y. Li, Z.-Z. Ma, F. Zhang, T.-T. Xu, Y.-T. Tian, D. Wu, X.-J. Li and G.-T. Du, High-Efficiency and Air-Stable Photodetectors Based on Lead-Free Double Perovskite Cs2AgBiBr6 Thin Films, J. Mater. Chem. C, 2018, 6(30), 7982–7988,  10.1039/C8TC02305K.
25. S. E. Creutz, E. N. Crites, M. C. De Siena and D. R. Gamelin, Colloidal Nanocrystals of Lead-Free Double-Perovskite (Elpasolite) Semiconductors: Synthesis and Anion Exchange To Access New Materials, Nano Lett., 2018, 18(2), 1118–1123,  DOI:10.1021/acs.nanolett.7b04659.
26. J. Li, L. Wang, X. Yuan, B. Bo, H. Li, J. Zhao and X. Gao, Ultraviolet Light Induced Degradation of Luminescence in CsPbBr3 Perovskite Nanocrystals, Mater. Res. Bull., 2018, 102, 86–91,  DOI:10.1016/j.materresbull.2018.02.021.
27. S.-H. Guo, J. Zhou, X. Zhao, C.-Y. Sun, S.-Q. You, X.-L. Wang and Z.-M. Su, Enhanced CO₂ Photoreduction via Tuning Halides in Perovskites, J. Catal., 2019, 369, 201–208,  DOI:10.1016/j.jcat.2018.11.004.
28. J. H. Noh, S. H. Im, J. H. Heo, T. N. Mandal and S. I. Seok, Chemical Management for Colorful, Efficient, and Stable Inorganic–Organic Hybrid Nanostructured Solar Cells, Nano Lett., 2013, 13(4), 1764–1769,  DOI:10.1021/nl400349b.
29. M. Knezevic, V.-D. Quach, I. Lampre, M. Erard, P. Pernot, D. Berardan, C. Colbeau-Justin and M. N. Ghazzal, Adjusting the Band Gap of CsPbBr3−yXy (X = Cl, I) for Optimal Interfacial Charge Transfer and Enhanced Photocatalytic Hydrogen Generation, J. Mater. Chem. A, 2023, 11(12), 6226–6236,  10.1039/D2TA09920A.
30. M. Knezevic, T.-H. Hoang, C. Wang, M. Johar, A. G. Manjón, D. L. Rauret, C. Scheu, M. Erard, D. Berardan, J. Arbiol, C. Colbeau-Justin and M. N. Ghazzal, Amplified Photoluminescence of CsPbX3 Perovskites Confined in Silica Film with a Chiral Nematic Structure, Adv. Mater. Interfaces, 2024, 11(3), 2300636,  DOI:10.1002/admi.202300636.
31. L.-Y. Wu, M.-R. Zhang, Y.-X. Feng, W. Zhang, M. Zhang and T.-B. Lu, Two-Dimensional Metal Halide Perovskite Nanosheets for Efficient Photocatalytic CO2 Reduction, Sol. RRL, 2021, 5(8), 2100263,  DOI:10.1002/solr.202100263.
32. I. C. Smith, E. T. Hoke, D. Solis-Ibarra, M. D. McGehee and H. I. Karunadasa, A Layered Hybrid Perovskite Solar-Cell Absorber with Enhanced Moisture Stability, Angew. Chem., Int. Ed., 2014, 53(42), 11232–11235,  DOI:10.1002/anie.201406466.
33. J. Byun, H. Cho, C. Wolf, M. Jang, A. Sadhanala, R. H. Friend, H. Yang and T.-W. Lee, Efficient Visible Quasi-2D Perovskite Light-Emitting Diodes, Adv. Mater., 2016, 28(34), 7515–7520,  DOI:10.1002/adma.201601369.
34. M. Knezevic, T.-H. Hoang, V. D. Quach, A. Garzón Manjón, D. Llorens Rauret, M. Erard, A. Gayral, M. Benoit, D. Berardan, J. Arbiol, C. Colbeau-Justin and M. N. Ghazzal, Impact of Bi³⁺ and Cu²⁺ Doping on the Optical and Electronic Properties of CsPbBr₃ for Photocatalytic Toluene Oxidation, Nanoscale, 2025, 17(35), 20280–20291,  10.1039/D5NR02442K.
35. X. Jiang, Q. Zhou, Y. Lu, H. Liang, W. Li, Q. Wei, M. Pan, X. Wen, X. Wang, W. Zhou, D. Yu, H. Wang, N. Yin, H. Chen, H. Li, T. Pan, M. Ma, G. Liu, W. Zhou, Z. Su, Q. Chen, F. Fan, F. Zheng, X. Gao, Q. Ji and Z. Ning, Surface Heterojunction Based on N-Type Low-Dimensional Perovskite Film for Highly Efficient Perovskite Tandem Solar Cells, Natl. Sci. Rev., 2024, 11(5), nwae055,  DOI:10.1093/nsr/nwae055.
36. J. Euvrard, Y. Yan and D. B. Mitzi, Electrical Doping in Halide Perovskites, Nat. Rev. Mater., 2021, 6(6), 531–549,  DOI:10.1038/s41578-021-00286-z.
37. J. Thiesbrummel, J. V. Milić, C. Deibel, E. C. Garnett, S. Tao, T. Kirchartz, A. Guerrero, P. Cameron, W. Tress, M. Saiful Islam and B. Ehrler, Ion Migration in Perovskite Solar Cells, Nat. Rev. Chem., 2026, 10(3), 179–195,  DOI:10.1038/s41570-025-00790-8.
38. X. Li, M. Ibrahim Dar, C. Yi, J. Luo, M. Tschumi, S. M. Zakeeruddin, M. K. Nazeeruddin, H. Han and M. Grätzel, Improved Performance and Stability of Perovskite Solar Cells by Crystal Crosslinking with Alkylphosphonic Acid ω-Ammonium Chlorides, Nat. Chem., 2015, 7(9), 703–711,  DOI:10.1038/nchem.2324.
39. W. Song, Y. Wang, C. Wang, B. Wang, J. Feng, W. Luo, C. Wu, Y. Yao and Z. Zou, Photocatalytic Hydrogen Production by Stable CsPbBr3@PANI Nanoparticles in Aqueous Solution, ChemCatChem, 2021, 13(7), 1711–1716,  DOI:10.1002/cctc.202001955.
40. X. Li, Y. Wang, H. Sun and H. Zeng, Amino-Mediated Anchoring Perovskite Quantum Dots for Stable and Low-Threshold Random Lasing, Adv. Mater., 2017, 29(36), 1701185,  DOI:10.1002/adma.201701185.
41. J. M. Ball and A. Petrozza, Defects in Perovskite-Halides and Their Effects in Solar Cells, Nat. Energy, 2016, 1(11), 16149,  DOI:10.1038/nenergy.2016.149.
42. H. Jin, E. Debroye, M. Keshavarz, I. G. Scheblykin, M. B. J. Roeffaers, J. Hofkens and J. A. Steele, It's a Trap! On the Nature of Localised States and Charge Trapping in Lead Halide Perovskites, Mater. Horiz., 2020, 7(2), 397–410,  10.1039/C9MH00500E.
43. Y. Li, H. Wu, W. Qi, X. Zhou, J. Li, J. Cheng, Y. Zhao, Y. Li and X. Zhang, Passivation of Defects in Perovskite Solar Cell: From a Chemistry Point of View, Nano Energy, 2020, 77, 105237,  DOI:10.1016/j.nanoen.2020.105237.
44. Z. Guo, M. Yuan, G. Chen, F. Liu, R. Lu and W. Yin, Understanding Defects in Perovskite Solar Cells through Computation: Current Knowledge and Future Challenge, Adv. Sci., 2024, 11(20), 2305799,  DOI:10.1002/advs.202305799.
45. D. Xiang, Z. Ma, Y. Li, Z. Lv, B. Chen, K. Liu, H. Du, Q. Zhang, F. Gou, Z. Du, W. You, R. Xu, L. Chen, Y. Xiang, C. Huang, J. Yu, L. Zhu, Y. Ding, C. Tang, B. Luo, H. Guo, Y. Hu and K. Sun, Perovskite-Based Photoanode with Surface Defect Passivation for Efficient Photoelectrochemical Water Splitting, J. Alloys Compd., 2025, 1049, 185441,  DOI:10.1016/j.jallcom.2025.185441.
46. J. Sun, N. Liu, D. Wang, Q. Li and F. Qiu, Maximizing Defect Formation Energies via Collaborative Passivation Achieves High-Performance Perovskite Solar Cells, ACS Appl. Mater. Interfaces, 2025, 17(50), 67926–67933,  DOI:10.1021/acsami.5c18376.
47. Z. Zhu, B. Ke, K. Sun, C. Jin, Z. Song, R. Jiang, J. Li, S. Kong, C. Liu, S. Bai, S. He, Z. Ge, F. Huang, Y.-B. Cheng and T. Bu, High-Performance Inverted Perovskite Solar Cells and Modules via Aminothiazole Passivation, Energy Environ. Sci., 2025, 18(9), 4120–4129,  10.1039/D5EE01083G.
48. X. Xu, Z. Zhang, T. Liu, P. Zhu, Z. Zhang and G. Xing, Suppressing the Penetration of 2D Perovskites for Enhanced Stability of Perovskite Solar Cells, J. Mater. Chem. A, 2025, 13(17), 12097–12103,  10.1039/D4TA08811E.
49. J.-A. Li, H. Ma, X. Ding, S. Li, B. Han, W. Chen, S. Huang, S. Chen, Y. Kuang, Z. Liu and C. Yan, Synergistic Passivation and Stable Carrier Transport Enable Efficient Blade-Coated Perovskite Solar Cells Fabricated in Ambient Air, J. Mater. Chem. A, 2025, 13(36), 30140–30150,  10.1039/D5TA04703J.
50. A. Kumar, S. K. Gupta, B. P. Dhamaniya, S. K. Pathak and S. Karak, Understanding the Origin of Defect States, Their Nature, and Effects on Metal Halide Perovskite Solar Cells, Mater. Today Energy, 2023, 37, 101400,  DOI:10.1016/j.mtener.2023.101400.
51. J. Ye, M. M. Byranvand, C. O. Martínez, R. L. Z. Hoye, M. Saliba and L. Polavarapu, Defect Passivation in Lead-Halide Perovskite Nanocrystals and Thin Films: Toward Efficient LEDs and Solar Cells, Angew. Chem., Int. Ed., 2021, 60(40), 21636–21660,  DOI:10.1002/anie.202102360.
52. Z. Niazi and E. K. Goharshadi, Biopolymers for Perovskite Solar Cells, in Bio-Based Polymers: Farm to Industry. Volume 3: Emerging Trends and Applications; ACS Symposium Series, American Chemical Society, 2024, vol. 1487, pp 35–56,  DOI:10.1021/bk-2024-1487.ch003.
53. S. Wang, X.-Y. Gong, M.-X. Li, M.-H. Li and J.-S. Hu, Polymers for Perovskite Solar Cells, JACS Au, 2024, 4(9), 3400–3412,  DOI:10.1021/jacsau.4c00615.
54. H. Zou, H. Bi, Y. Chen, M. Guo, W. Hou, P. Su, K. Zhou, C. Yang, X. Gong, L. Xiao and L. Liu, Functionalized Polymer Modified Buried Interface for Enhanced Efficiency and Stability of Perovskite Solar Cells, Nanoscale, 2023, 15(5), 2054–2060,  10.1039/D2NR06290A.
55. S. S. Sangale, D. S. Mann, H.-J. Lee, S.-N. Kwon and S.-I. Na, Influence of Interfacial Roughness on Slot-Die Coatings for Scaling-up High-Performance Perovskite Solar Cells, Commun. Mater., 2024, 5(1), 201,  DOI:10.1038/s43246-024-00645-7.
56. T. Ji, T. Niu, J. Wang, R. Lu, Z. Wen, D. Luo, J. C. Huang, Y. Min, S. Wang, Y. N. Luponosov, S. Pan, Y. Chen and Q. Xue, Crystallization Regulation of Solution-Processed Two-Dimensional Perovskite Solar Cells, J. Mater. Chem. A, 2022, 10(26), 13625–13650,  10.1039/D2TA02574D.
57. Y. Hu, J. Schlipf, M. Wussler, M. L. Petrus, W. Jaegermann, T. Bein, P. Müller-Buschbaum and P. Docampo, Hybrid Perovskite/Perovskite Heterojunction Solar Cells, ACS Nano, 2016, 10(6), 5999–6007,  DOI:10.1021/acsnano.6b01535.
58. T. Liu and Z. Yang, Self-Healing Perovskite Solar Cells: Introduction, Recent Progresses and Perspective, SmartMat, 2025, 6(4), e70033,  DOI:10.1002/smm2.70033.
59. Y. Zhang, T. D. Siegler, C. J. Thomas, M. K. Abney, T. Shah, A. De Gorostiza, R. M. Greene and B. A. A. Korgel, “Tips and Tricks” Practical Guide to the Synthesis of Metal Halide Perovskite Nanocrystals, Chem. Mater., 2020, 32(13), 5410–5423,  DOI:10.1021/acs.chemmater.0c01735.
60. Q. Zheng, J. Wang, X. Li, Y. Bai, Y. Li, J. Wang, Y. Shi, X. Jiang and Z. Li, Surface Halogen Compensation on CsPbBr3 Nanocrystals with SOBr2 for Photocatalytic CO2 Reduction, ACS Mater. Lett., 2022, 4(9), 1638–1645,  DOI:10.1021/acsmaterialslett.2c00482.
61. J.-C. Wang, N. Li, A. M. Idris, J. Wang, X. Du, Z. Pan and Z. Li, Surface Defect Engineering of CsPbBr3 Nanocrystals for High Efficient Photocatalytic CO2 Reduction, Sol. RRL, 2021, 5(7), 2100154,  DOI:10.1002/solr.202100154.
62. J. Pan, Y. Shang, J. Yin, M. De Bastiani, W. Peng, I. Dursun, L. Sinatra, A. M. El-Zohry, M. N. Hedhili, A.-H. Emwas, O. F. Mohammed, Z. Ning and O. M. Bakr, Bidentate Ligand-Passivated CsPbI3 Perovskite Nanocrystals for Stable Near-Unity Photoluminescence Quantum Yield and Efficient Red Light-Emitting Diodes, J. Am. Chem. Soc., 2018, 140(2), 562–565,  DOI:10.1021/jacs.7b10647.
63. E. A. Alharbi, A. Y. Alyamani, D. J. Kubicki, A. R. Uhl, B. J. Walder, A. Q. Alanazi, J. Luo, A. Burgos-Caminal, A. Albadri, H. Albrithen, M. H. Alotaibi, J.-E. Moser, S. M. Zakeeruddin, F. Giordano, L. Emsley and M. Grätzel, Atomic-Level Passivation Mechanism of Ammonium Salts Enabling Highly Efficient Perovskite Solar Cells, Nat. Commun., 2019, 10(1), 3008,  DOI:10.1038/s41467-019-10985-5.
64. Y.-H. Kim, S. Kim, A. Kakekhani, J. Park, J. Park, Y.-H. Lee, H. Xu, S. Nagane, R. B. Wexler, D.-H. Kim, S. H. Jo, L. Martínez-Sarti, P. Tan, A. Sadhanala, G.-S. Park, Y.-W. Kim, B. Hu, H. J. Bolink, S. Yoo, R. H. Friend, A. M. Rappe and T.-W. Lee, Comprehensive Defect Suppression in Perovskite Nanocrystals for High-Efficiency Light-Emitting Diodes, Nat. Photonics, 2021, 15(2), 148–155,  DOI:10.1038/s41566-020-00732-4.
65. Y.-H. Kim, S. Kim, A. Kakekhani, J. Park, J. Park, Y.-H. Lee, H. Xu, S. Nagane, R. B. Wexler, D.-H. Kim, S. H. Jo, L. Martínez-Sarti, P. Tan, A. Sadhanala, G.-S. Park, Y.-W. Kim, B. Hu, H. J. Bolink, S. Yoo, R. H. Friend, A. M. Rappe and T.-W. Lee, Comprehensive Defect Suppression in Perovskite Nanocrystals for High-Efficiency Light-Emitting Diodes, Nat. Photonics, 2021, 15(2), 148–155,  DOI:10.1038/s41566-020-00732-4.
66. A. Liang, K. Wang, Y. Gao, B. P. Finkenauer, C. Zhu, L. Jin, L. Huang and L. Dou, Highly Efficient Halide Perovskite Light-Emitting Diodes via Molecular Passivation, Angew. Chem., Int. Ed., 2021, 60(15), 8337–8343,  DOI:10.1002/anie.202100243.
67. Z.-J. Bai, A.-J. Yang, S. Tian, L. Chen, B.-H. Wang, B. Hu, X. Wang, T.-Q. Zeng, C. Peng, Y. Mao, M. Tulu, C.-T. Au and S.-F. Yin, Multi-Dimensional Lead-Free Hybrid Double Perovskite toward Efficient and Stable Photocatalytic Selective Oxidation of Toluene, Chem. Eng. Sci., 2023, 282, 119334,  DOI:10.1016/j.ces.2023.119334.
68. Z. Fang, W. Chen, Y. Shi, J. Zhao, S. Chu, J. Zhang and Z. Xiao, Dual Passivation of Perovskite Defects for Light-Emitting Diodes with External Quantum Efficiency Exceeding 20%, Adv. Funct. Mater., 2020, 30(12), 1909754,  DOI:10.1002/adfm.201909754.
69. X. Zheng, Y. Deng, B. Chen, H. Wei, X. Xiao, Y. Fang, Y. Lin, Z. Yu, Y. Liu, Q. Wang and J. Huang, Dual Functions of Crystallization Control and Defect Passivation Enabled by Sulfonic Zwitterions for Stable and Efficient Perovskite Solar Cells, Adv. Mater., 2018, 30(52), 1803428,  DOI:10.1002/adma.201803428.
70. K. Choi, J. Lee, H. I. Kim, C. W. Park, G.-W. Kim, H. Choi, S. Park, S. A. Park and T. Park, Thermally Stable, Planar Hybrid Perovskite Solar Cells with High Efficiency, Energy Environ. Sci., 2018, 11(11), 3238–3247,  10.1039/C8EE02242A.
71. Y. Yang, H. Peng, C. Liu, Z. Arain, Y. Ding, S. Ma, X. Liu, T. Hayat, A. Alsaedi and S. Dai, Bi-Functional Additive Engineering for High-Performance Perovskite Solar Cells with Reduced Trap Density, J. Mater. Chem. A, 2019, 7(11), 6450–6458,  10.1039/C8TA11925B.
72. J. Ciro, S. Mesa, J. I. Uribe, M. A. Mejía-Escobar, D. Ramirez, J. F. Montoya, R. Betancur, H.-S. Yoo, N.-G. Park and F. Jaramillo, Optimization of the Ag/PCBM Interface by a Rhodamine Interlayer to Enhance the Efficiency and Stability of Perovskite Solar Cells, Nanoscale, 2017, 9(27), 9440–9446,  10.1039/C7NR01678F.
73. J.-H. Kim, Y. R. Kim, B. Park, S. Hong, I.-W. Hwang, J. Kim, S. Kwon, G. Kim, H. Kim and K. Lee, Simultaneously Passivating Cation and Anion Defects in Metal Halide Perovskite Solar Cells Using a Zwitterionic Amino Acid Additive, Small, 2021, 17(3), 2005608,  DOI:10.1002/smll.202005608.
74. L. Zhang, K. Cao, J. Qian, Y. Huang, X. Wang, M. Ge, W. Shen, F. Huang, M. Wang, W. Zhang, S. Chen and T. Qin, Crystallization Control and Multisite Passivation of Perovskites with Amino Acid to Boost the Efficiency and Stability of Perovskite Solar Cells, J. Mater. Chem. C, 2020, 8(48), 17482–17490,  10.1039/D0TC04186F.
75. Y. Cho, A. M. Soufiani, J. S. Yun, J. Kim, D. S. Lee, J. Seidel, X. Deng, M. A. Green, S. Huang and A. W. Y. Ho-Baillie, Mixed 3D–2D Passivation Treatment for Mixed-Cation Lead Mixed-Halide Perovskite Solar Cells for Higher Efficiency and Better Stability, Adv. Energy Mater., 2018, 8(20), 1703392,  DOI:10.1002/aenm.201703392.
76. M. M. Tavakoli, P. Yadav, D. Prochowicz, M. Sponseller, A. Osherov, V. Bulović and J. Kong, Controllable Perovskite Crystallization via Antisolvent Technique Using Chloride Additives for Highly Efficient Planar Perovskite Solar Cells, Adv. Energy Mater., 2019, 9(17), 1803587,  DOI:10.1002/aenm.201803587.
77. S. Lee, J. H. Park, B. R. Lee, E. D. Jung, J. C. Yu, D. Di Nuzzo, R. H. Friend and M. H. Song, Amine-Based Passivating Materials for Enhanced Optical Properties and Performance of Organic–Inorganic Perovskites in Light-Emitting Diodes, J. Phys. Chem. Lett., 2017, 8(8), 1784–1792,  DOI:10.1021/acs.jpclett.7b00372.
78. F. Wang, W. Geng, Y. Zhou, H.-H. Fang, C.-J. Tong, M. A. Loi, L.-M. Liu and N. Zhao, Phenylalkylamine Passivation of Organolead Halide Perovskites Enabling High-Efficiency and Air-Stable Photovoltaic Cells, Adv. Mater., 2016, 28(45), 9986–9992,  DOI:10.1002/adma.201603062.
79. Y. Zhou, F. Wang, Y. Cao, J.-P. Wang, H.-H. Fang, M. A. Loi, N. Zhao and C.-P. Wong, Benzylamine-Treated Wide-Bandgap Perovskite with High Thermal-Photostability and Photovoltaic Performance, Adv. Energy Mater., 2017, 7(22), 1701048,  DOI:10.1002/aenm.201701048.
80. Y.-Z. Zheng, X.-T. Li, E.-F. Zhao, X.-D. Lv, F.-L. Meng, C. Peng, X.-S. Lai, M. Huang, G. Cao, X. Tao and J.-F. Chen, Hexamethylenetetramine-Mediated Growth of Grain-Boundary-Passivation CH3NH3PbI3 for Highly Reproducible and Stable Perovskite Solar Cells, J. Power Sources, 2018, 377, 103–109,  DOI:10.1016/j.jpowsour.2017.12.011.
81. S.-G. Kim, J. Chen, J.-Y. Seo, D.-H. Kang and N.-G. Park, Rear-Surface Passivation by Melaminium Iodide Additive for Stable and Hysteresis-Less Perovskite Solar Cells, ACS Appl. Mater. Interfaces, 2018, 10(30), 25372–25383,  DOI:10.1021/acsami.8b06616.
82. L. Xu, J. Li, B. Cai, J. Song, F. Zhang, T. Fang and H. A. Zeng, Bilateral Interfacial Passivation Strategy Promoting Efficiency and Stability of Perovskite Quantum Dot Light-Emitting Diodes, Nat. Commun., 2020, 11(1), 3902,  DOI:10.1038/s41467-020-17633-3.
83. R. Wang, J. Xue, K.-L. Wang, Z.-K. Wang, Y. Luo, D. Fenning, G. Xu, S. Nuryyeva, T. Huang, Y. Zhao, J. L. Yang, J. Zhu, M. Wang, S. Tan, I. Yavuz, K. N. Houk and Y. Yang, Constructive Molecular Configurations for Surface-Defect Passivation of Perovskite Photovoltaics, Science, 2019, 366(6472), 1509–1513,  DOI:10.1126/science.aay9698.
84. X. Li, C.-C. Chen, M. Cai, X. Hua, F. Xie, X. Liu, J. Hua, Y.-T. Long, H. Tian and L. Han, Efficient Passivation of Hybrid Perovskite Solar Cells Using Organic Dyes with COOH Functional Group, Adv. Energy Mater., 2018, 8(20), 1800715,  DOI:10.1002/aenm.201800715.
85. J. Zhang and H. Yu, Reduced Energy Loss Enabled by Thiophene-Based Interlayers for High Performance and Stable Perovskite Solar Cells, J. Mater. Chem. A, 2021, 9(7), 4138–4149,  10.1039/D0TA10270A.
86. G. Qu, D. Khan, F. Yan, A. Atsay, H. Xiao, Q. Chen, H. Xu, I. Nar and Z.-X. Xu, Reformation of Thiophene-Functionalized Phthalocyanine Isomers for Defect Passivation to Achieve Stable and Efficient Perovskite Solar Cells, J. Energy Chem., 2022, 67, 263–275,  DOI:10.1016/j.jechem.2021.09.041.
87. J. Cao, J. Yin, S. Yuan, Y. Zhao, J. Li and N. Zheng, Thiols as Interfacial Modifiers to Enhance the Performance and Stability of Perovskite Solar Cells, Nanoscale, 2015, 7(21), 9443–9447,  10.1039/C5NR01820J.
88. T. Xu, Y. Xie, S. Qi, H. Zhang, W. Ma, J. Wang, Y. Gao, L. Wang and X. Zong, Simultaneous Defect Passivation and Co-Catalyst Engineering Leads to Superior Photocatalytic Hydrogen Evolution on Metal Halide Perovskites, Angew. Chem., Int. Ed., 2024, 63(41), e202409945,  DOI:10.1002/anie.202409945.
89. G. Meng, L. Zhen, S. Sun, J. Hai, Z. Zhang, D. Sun, Q. Liu and B. Wang, Confining Perovskite Quantum Dots in the Pores of a Covalent-Organic Framework: Quantum Confinement- and Passivation-Enhanced Light-Harvesting and Photocatalysis, J. Mater. Chem. A, 2021, 9(43), 24365–24373,  10.1039/D1TA07733C.
90. M. Li, X. Yan, Z. Kang, Y. Huan, Y. Li, R. Zhang and Y. Zhang, Hydrophobic Polystyrene Passivation Layer for Simultaneously Improved Efficiency and Stability in Perovskite Solar Cells, ACS Appl. Mater. Interfaces, 2018, 10(22), 18787–18795,  DOI:10.1021/acsami.8b04776.
91. M. Kim, S. G. Motti, R. Sorrentino and A. Petrozza, Enhanced Solar Cell Stability by Hygroscopic Polymer Passivation of Metal Halide Perovskite Thin Film, Energy Environ. Sci., 2018, 11(9), 2609–2619,  10.1039/C8EE01101J.
92. W. Feng, Y. Zhao, K. Lin, J. Lu, Y. Liang, K. Liu, L. Xie, C. Tian, T. Lyu and Z. Wei, Polymer-Assisted Crystal Growth Regulation and Defect Passivation for Efficient Perovskite Light-Emitting Diodes, Adv. Funct. Mater., 2022, 32(34), 2203371,  DOI:10.1002/adfm.202203371.
93. J. Peng, J. I. Khan, W. Liu, E. Ugur, T. Duong, Y. Wu, H. Shen, K. Wang, H. Dang, E. Aydin, X. Yang, Y. Wan, K. J. Weber, K. R. Catchpole, F. Laquai, S. De Wolf and T. P. White, A Universal Double-Side Passivation for High Open-Circuit Voltage in Perovskite Solar Cells: Role of Carbonyl Groups in Poly(Methyl Methacrylate), Adv. Energy Mater., 2018, 8(30), 1801208,  DOI:10.1002/aenm.201801208.
94. J. Li, X. Shan, S. G. R. Bade, T. Geske, Q. Jiang, X. Yang and Z. Yu, Single-Layer Halide Perovskite Light-Emitting Diodes with Sub-Band Gap Turn-On Voltage and High Brightness, J. Phys. Chem. Lett., 2016, 7(20), 4059–4066,  DOI:10.1021/acs.jpclett.6b01942.
95. L. Song, X. Guo, Y. Hu, Y. Lv, J. Lin, Z. Liu, Y. Fan and X. Liu, Efficient Inorganic Perovskite Light-Emitting Diodes with Polyethylene Glycol Passivated Ultrathin CsPbBr3 Films, J. Phys. Chem. Lett., 2017, 8(17), 4148–4154,  DOI:10.1021/acs.jpclett.7b01733.
96. Y. Lao, S. Yang, W. Yu, H. Guo, Y. Zou, Z. Chen and L. Xiao, Multifunctional π-Conjugated Additives for Halide Perovskite, Adv. Sci., 2022, 9(17), 2105307,  DOI:10.1002/advs.202105307.
97. Y. Lin, L. Shen, J. Dai, Y. Deng, Y. Wu, Y. Bai, X. Zheng, J. Wang, Y. Fang, H. Wei, W. Ma, X. C. Zeng, X. Zhan and J. Huang, π-Conjugated Lewis Base: Efficient Trap-Passivation and Charge-Extraction for Hybrid Perovskite Solar Cells, Adv. Mater., 2017, 29(7), 1604545,  DOI:10.1002/adma.201604545.
98. K. Wang, J. Liu, J. Yin, E. Aydin, G. T. Harrison, W. Liu, S. Chen, O. F. Mohammed and S. De Wolf, Defect Passivation in Perovskite Solar Cells by Cyano-Based π-Conjugated Molecules for Improved Performance and Stability, Adv. Funct. Mater., 2020, 30(35), 2002861,  DOI:10.1002/adfm.202002861.
99. Y. Park, A. Jana, C. W. Myung, T. Yoon, G. Lee, C. C. Kocher, G. Ying, V. Osokin, R. A. Taylor and K. S. Kim, Enhanced Photoluminescence Quantum Yield of MAPbBr3 Nanocrystals by Passivation Using Graphene, Nano Res., 2020, 13(4), 932–938,  DOI:10.1007/s12274-020-2718-8.
100. Y.-F. Xu, M.-Z. Yang, B.-X. Chen, X.-D. Wang, H.-Y. Chen, D.-B. Kuang and C.-Y. Su, A CsPbBr3 Perovskite Quantum Dot/Graphene Oxide Composite for Photocatalytic CO2 Reduction, J. Am. Chem. Soc., 2017, 139(16), 5660–5663,  DOI:10.1021/jacs.7b00489.
101. Y. Bai, Y. Lin, L. Ren, X. Shi, E. Strounina, Y. Deng, Q. Wang, Y. Fang, X. Zheng, Y. Lin, Z.-G. Chen, Y. Du, L. Wang and J. Huang, Oligomeric Silica-Wrapped Perovskites Enable Synchronous Defect Passivation and Grain Stabilization for Efficient and Stable Perovskite Photovoltaics, ACS Energy Lett., 2019, 4(6), 1231–1240,  DOI:10.1021/acsenergylett.9b00608.
102. S. Purohit, S. Singh, K. L. Yadav, K. K. Pant and S. Satapathi, Enhanced CO2 Reduction with Cs2AgBiBr6-gC3N4 Heterojunction Photocatalysts Prepared by Green Synthesis, ACS Appl. Energy Mater., 2023, 6(10), 5580–5587,  DOI:10.1021/acsaem.3c00717.
103. L. Jia, M. Chen and S. Yang, Functionalization of Fullerene Materials toward Applications in Perovskite Solar Cells, Mater. Chem. Front., 2020, 4(8), 2256–2282,  10.1039/D0QM00295J.
104. Y. Shao, Z. Xiao, C. Bi, Y. Yuan and J. Huang, Origin and Elimination of Photocurrent Hysteresis by Fullerene Passivation in CH3NH3PbI3 Planar Heterojunction Solar Cells, Nat. Commun., 2014, 5(1), 5784,  DOI:10.1038/ncomms6784.
105. T. Niu, J. Lu, R. Munir, J. Li, D. Barrit, X. Zhang, H. Hu, Z. Yang, A. Amassian, K. Zhao and S. Liu, Stable High-Performance Perovskite Solar Cells via Grain Boundary Passivation, Adv. Mater., 2018, 30(16), 1706576,  DOI:10.1002/adma.201706576.
106. F. Zhang, W. Shi, J. Luo, N. Pellet, C. Yi, X. Li, X. Zhao, T. J. S. Dennis, X. Li, S. Wang, Y. Xiao, S. M. Zakeeruddin, D. Bi and M. Grätzel, Isomer-Pure Bis-PCBM-Assisted Crystal Engineering of Perovskite Solar Cells Showing Excellent Efficiency and Stability, Adv. Mater., 2017, 29(17), 1606806,  DOI:10.1002/adma.201606806.
107. F. Zhang, D. Bi, N. Pellet, C. Xiao, Z. Li, J. J. Berry, S. M. Zakeeruddin, K. Zhu and M. Grätzel, Suppressing Defects through the Synergistic Effect of a Lewis Base and a Lewis Acid for Highly Efficient and Stable Perovskite Solar Cells, Energy Environ. Sci., 2018, 11(12), 3480–3490,  10.1039/C8EE02252F.
108. P.-P. Cheng, Y.-W. Zhang, J.-M. Liang, W.-Y. Tan, X. Chen, Y. Liu and Y. Min, A Facile Route to Surface Passivation of Both the Positive and Negative Defects in Perovskite Solar Cells via a Self-Organized Passivation Layer from Fullerene, Sol. Energy, 2019, 190, 264–271,  DOI:10.1016/j.solener.2019.08.026.
109. M. Zhang, Q. Chen, R. Xue, Y. Zhan, C. Wang, J. Lai, J. Yang, H. Lin, J. Yao, Y. Li, L. Chen and Y. Li, Reconfiguration of Interfacial Energy Band Structure for High-Performance Inverted Structure Perovskite Solar Cells, Nat. Commun., 2019, 10(1), 4593,  DOI:10.1038/s41467-019-12613-8.
110. Z. Yang, J. Dou, S. Kou, J. Dang, Y. Ji, G. Yang, W.-Q. Wu, D.-B. Kuang and M. Wang, Multifunctional Phosphorus-Containing Lewis Acid and Base Passivation Enabling Efficient and Moisture-Stable Perovskite Solar Cells, Adv. Funct. Mater., 2020, 30(15), 1910710,  DOI:10.1002/adfm.201910710.
111. A. Abate, M. Saliba, D. J. Hollman, S. D. Stranks, K. Wojciechowski, R. Avolio, G. Grancini, A. Petrozza and H. J. Snaith, Supramolecular Halogen Bond Passivation of Organic–Inorganic Halide Perovskite Solar Cells, Nano Lett., 2014, 14(6), 3247–3254,  DOI:10.1021/nl500627x.
112. D. Song, D. Wei, P. Cui, M. Li, Z. Duan, T. Wang, J. Ji, Y. Li, J. M. Mbengue, Y. Li, Y. He, M. Trevor and N.-G. Park, Dual Function Interfacial Layer for Highly Efficient and Stable Lead Halide Perovskite Solar Cells, J. Mater. Chem. A, 2016, 4(16), 6091–6097,  10.1039/C6TA00577B.
113. M. Abdi-Jalebi, M. Pazoki, B. Philippe, M. I. Dar, M. Alsari, A. Sadhanala, G. Divitini, R. Imani, S. Lilliu, J. Kullgren, H. Rensmo, M. Grätzel and R. H. Friend, Dedoping of Lead Halide Perovskites Incorporating Monovalent Cations, ACS Nano, 2018, 12(7), 7301–7311,  DOI:10.1021/acsnano.8b03586.
114. T. Hu, Y. Wang, K. Liu, J. Liu, H. Zhang, Q. U. Khan, S. Dai, W. Qian, R. Liu, Y. Wang, C. Li, Z. Zhang, M. Luo, X. Yue, C. Cong, Y. Yongbo, A. Yu, J. Zhang and Y. Zhan, Understanding the Decoupled Effects of Cations and Anions Doping for High-Performance Perovskite Solar Cells, Nano-Micro Lett., 2025, 17(1), 145,  DOI:10.1007/s40820-025-01655-x.
115. Y. Lu, F. Alam, J. Shamsi and M. Abdi-Jalebi, Doping Up the Light: A Review of A/B-Site Doping in Metal Halide Perovskite Nanocrystals for Next-Generation LEDs, J. Phys. Chem. C, 2024, 128(24), 10084–10107,  DOI:10.1021/acs.jpcc.4c00749.
116. S. Bera, A. Saha, S. Mondal, A. Biswas, S. Mallick, R. Chatterjee and S. Roy, Review of Defect Engineering in Perovskites for Photovoltaic Application, Mater. Adv., 2022, 3(13), 5234–5247,  10.1039/D2MA00194B.
117. L. Wu, M. Zhang, S. Yang, R. Wu, S. Gong, Q. Han and W. Wu, Spectral and Dynamic Analysis of CsPbBr3 Perovskite Nanocrystals with Enhanced Water Stability Using Sodium Passivation, J. Alloys Compd., 2021, 889, 161721,  DOI:10.1016/j.jallcom.2021.161721.
118. C. Bi, X. Zheng, B. Chen, H. Wei and J. Huang, Spontaneous Passivation of Hybrid Perovskite by Sodium Ions from Glass Substrates: Mysterious Enhancement of Device Efficiency Revealed, ACS Energy Lett., 2017, 2(6), 1400–1406,  DOI:10.1021/acsenergylett.7b00356.
119. M. Zhang, W. Hu, Y. Shang, W. Zhou, W. Zhang and S. Yang, Surface Passivation of Perovskite Film by Sodium Toluenesulfonate for Highly Efficient Solar Cells, Sol. RRL, 2020, 4(6), 2000113,  DOI:10.1002/solr.202000113.
120. J. Zhang, C. Yin, F. Yang, Y. Yao, F. Yuan, H. Chen, R. Wang, S. Bai, G. Tu and L. Hou, Highly Luminescent and Stable CsPbI3 Perovskite Nanocrystals with Sodium Dodecyl Sulfate Ligand Passivation for Red-Light-Emitting Diodes, J. Phys. Chem. Lett., 2021, 12(9), 2437–2443,  DOI:10.1021/acs.jpclett.1c00008.
121. D.-Y. Son, S.-G. Kim, J.-Y. Seo, S.-H. Lee, H. Shin, D. Lee and N.-G. Park, Universal Approach toward Hysteresis-Free Perovskite Solar Cell via Defect Engineering, J. Am. Chem. Soc., 2018, 140(4), 1358–1364,  DOI:10.1021/jacs.7b10430.
122. M. Abdi-Jalebi, Z. Andaji-Garmaroudi, S. Cacovich, C. Stavrakas, B. Philippe, J. M. Richter, M. Alsari, E. P. Booker, E. M. Hutter, A. J. Pearson, S. Lilliu, T. J. Savenije, H. Rensmo, G. Divitini, C. Ducati, R. H. Friend and S. D. Stranks, Maximizing and Stabilizing Luminescence from Halide Perovskites with Potassium Passivation, Nature, 2018, 555(7697), 497–501,  DOI:10.1038/nature25989.
123. T. Bu, X. Liu, Y. Zhou, J. Yi, X. Huang, L. Luo, J. Xiao, Z. Ku, Y. Peng, F. Huang, Y.-B. Cheng and J. Zhong, A Novel Quadruple-Cation Absorber for Universal Hysteresis Elimination for High Efficiency and Stable Perovskite Solar Cells, Energy Environ. Sci., 2017, 10(12), 2509–2515,  10.1039/C7EE02634J.
124. D. Yue, T. Zhang, T. Wang, X. Yan, C. Guo, X. Qian and Y. Zhao, Potassium Stabilization of Methylammonium Lead Bromide Perovskite for Robust Photocatalytic H2 Generation, EcoMat, 2020, 2(1), e12015,  DOI:10.1002/eom2.12015.
125. M. Abdi-Jalebi, Z. Andaji-Garmaroudi, A. J. Pearson, G. Divitini, S. Cacovich, B. Philippe, H. Rensmo, C. Ducati, R. H. Friend and S. D. Stranks, Potassium- and Rubidium-Passivated Alloyed Perovskite Films: Optoelectronic Properties and Moisture Stability, ACS Energy Lett., 2018, 3(11), 2671–2678,  DOI:10.1021/acsenergylett.8b01504.
126. Y. Guo, F. Zhao, J. Tao, J. Jiang, J. Zhang, J. Yang, Z. Hu and J. Chu, Efficient and Hole-Transporting-Layer-Free CsPbI2Br Planar Heterojunction Perovskite Solar Cells through Rubidium Passivation, ChemSusChem, 2019, 12(5), 983–989,  DOI:10.1002/cssc.201802690.
127. C. Xu, X. Chen, S. Ma, M. Shi, S. Zhang, Z. Xiong, W. Fan, H. Si, H. Wu, Z. Zhang, Q. Liao, W. Yin, Z. Kang and Y. Zhang, Interpretation of Rubidium-Based Perovskite Recipes toward Electronic Passivation and Ion-Diffusion Mitigation, Adv. Mater., 2022, 34(14), 2109998,  DOI:10.1002/adma.202109998.
128. D. J. Kubicki, D. Prochowicz, A. Hofstetter, S. M. Zakeeruddin, M. Grätzel and L. Emsley, Phase Segregation in Cs-, Rb- and K-Doped Mixed-Cation (MA)x(FA)1–xPbI3 Hybrid Perovskites from Solid-State NMR, J. Am. Chem. Soc., 2017, 139(40), 14173–14180,  DOI:10.1021/jacs.7b07223.
129. X. Ling, S. Zhou, J. Yuan, J. Shi, Y. Qian, B. W. Larson, Q. Zhao, C. Qin, F. Li, G. Shi, C. Stewart, J. Hu, X. Zhang, J. M. Luther, S. Duhm and W. Ma, 14.1% CsPbI3 Perovskite Quantum Dot Solar Cells via Cesium Cation Passivation, Adv. Energy Mater., 2019, 9(28), 1900721,  DOI:10.1002/aenm.201900721.
130. S. Yuan, Y. Cai, S. Yang, H. Zhao, F. Qian, Y. Han, J. Sun, Z. Liu and S. Liu, Simultaneous Cesium and Acetate Coalloying Improves Efficiency and Stability of FA0.85MA0.15PbI3 Perovskite Solar Cell with an Efficiency of 21.95, Sol. RRL, 2019, 3(9), 1900220,  DOI:10.1002/solr.201900220.
131. Y. Zhang, C. Wu, D. Wang, Z. Zhang, X. Qi, N. Zhu, G. Liu, X. Li, H. Hu, Z. Chen, L. Xiao and B. Qu, High Efficiency (16.37%) of Cesium Bromide—Passivated All-Inorganic CsPbI2Br Perovskite Solar Cells, Sol. RRL, 2019, 3(11), 1900254,  DOI:10.1002/solr.201900254.
132. X. Guo, T. M. Koh, B. Febriansyah, G. Han, S. Bhaumik, J. Li, N. F. Jamaludin, B. Ghosh, X. Chen, S. Mhaisalkar and N. Mathews, Cesium Oleate Passivation for Stable Perovskite Photovoltaics, ACS Appl. Mater. Interfaces, 2019, 11(31), 27882–27889,  DOI:10.1021/acsami.9b08026.
133. M. Abdi-Jalebi, M. Pazoki, B. Philippe, M. I. Dar, M. Alsari, A. Sadhanala, G. Divitini, R. Imani, S. Lilliu, J. Kullgren, H. Rensmo, M. Grätzel and R. H. Friend, Dedoping of Lead Halide Perovskites Incorporating Monovalent Cations, ACS Nano, 2018, 12(7), 7301–7311,  DOI:10.1021/acsnano.8b03586.
134. M. Lu, X. Zhang, X. Bai, H. Wu, X. Shen, Y. Zhang, W. Zhang, W. Zheng, H. Song, W. W. Yu and A. L. Rogach, Spontaneous Silver Doping and Surface Passivation of CsPbI3 Perovskite Active Layer Enable Light-Emitting Devices with an External Quantum Efficiency of 11.2%, ACS Energy Lett., 2018, 3(7), 1571–1577,  DOI:10.1021/acsenergylett.8b00835.
135. Q. Chen, L. Chen, F. Ye, T. Zhao, F. Tang, A. Rajagopal, Z. Jiang, S. Jiang, A. K.-Y. Jen, Y. Xie, J. Cai and L. Chen, Ag-Incorporated Organic–Inorganic Perovskite Films and Planar Heterojunction Solar Cells, Nano Lett., 2017, 17(5), 3231–3237,  DOI:10.1021/acs.nanolett.7b00847.
136. X. Gong, L. Guan, H. Pan, Q. Sun, X. Zhao, H. Li, H. Pan, Y. Shen, Y. Shao, L. Sun, Z. Cui, L. Ding and M. Wang, Highly Efficient Perovskite Solar Cells via Nickel Passivation, Adv. Funct. Mater., 2018, 28(50), 1804286,  DOI:10.1002/adfm.201804286.
137. R. Chakraborty, A. Maiti, U. K. Ghorai and A. J. Pal, Defect Passivation of Mn2+-Doped CsPbCl3 Perovskite Nanocrystals as Probed by Scanning Tunneling Spectroscopy: Toward Boosting Emission Efficiencies, ACS Appl. Nano Mater., 2021, 4(10), 10155–10163,  DOI:10.1021/acsanm.1c01623.
138. W. Zhao, J. Shi, C. Tian, J. Wu, H. Li, Y. Li, B. Yu, Y. Luo, H. Wu, Z. Xie, C. Wang, D. Duan, D. Li and Q. Meng, CdS Induced Passivation toward High Efficiency and Stable Planar Perovskite Solar Cells, ACS Appl. Mater. Interfaces, 2021, 13(8), 9771–9780,  DOI:10.1021/acsami.0c18311.
139. W.-Q. Wu, P. N. Rudd, Z. Ni, C. H. Van Brackle, H. Wei, Q. Wang, B. R. Ecker, Y. Gao and J. Huang, Reducing Surface Halide Deficiency for Efficient and Stable Iodide-Based Perovskite Solar Cells, J. Am. Chem. Soc., 2020, 142(8), 3989–3996,  DOI:10.1021/jacs.9b13418.
140. M. Ji, M. Jin, Q. Du, J. Zheng, Y. Feng, Z. Shen, F. Li, H. Li and C. Chen, Defect Passivation with Metal Cations toward Efficient and Stable Perovskite Solar Cells Exceeding 22.7% Efficiency, ACS Appl. Energy Mater., 2021, 4(10), 11144–11150,  DOI:10.1021/acsaem.1c02048.
141. L. Yan, Z. Li, T. Niu, X. Xu, S. Xie, G. Dong, Q. Xue and H.-L. Yip, Effects of ZnI2 Doping on the Performance of Methylammonium-Free Perovskite Solar Cells, J. Appl. Phys., 2020, 128(4), 043102,  DOI:10.1063/5.0012370.
142. L. Xiong, M. Xu, J. Wang, Z. Chen, L. Li, F. Yang, Q. Zhang, G. Jiang and Z. Li, Passivating Defects and Constructing Catalytic Sites on CsPbBr3 with ZnBr2 for Photocatalytic CO2 Reduction, Inorg. Chem., 2024, 63(28), 12703–12707,  DOI:10.1021/acs.inorgchem.4c02313.
143. Q. Chen, S. Cao, K. Xing, M. Ning, R. Zeng, Y. Wang and J. Zhao, Mg2+-Assisted Passivation of Defects in CsPbI3 Perovskite Nanocrystals for High-Efficiency Photoluminescence, J. Phys. Chem. Lett., 2021, 12(45), 11090–11097,  DOI:10.1021/acs.jpclett.1c03258.
144. W. Shen, J. Zhang, R. Dong, Y. Chen, L. Yang, S. Chen, Z. Su, Y. Dai, K. Cao, L. Liu, S. Chen and W. Huang, Stable and Efficient Red Perovskite Light-Emitting Diodes Based on Ca²⁺-Doped CsPbI₃ Nanocrystals, Research, 2021,  DOI:10.34133/2021/9829374.
145. J.-K. Chen, J.-P. Ma, S.-Q. Guo, Y.-M. Chen, Q. Zhao, B.-B. Zhang, Z.-Y. Li, Y. Zhou, J. Hou, Y. Kuroiwa, C. Moriyoshi, O. M. Bakr, J. Zhang and H.-T. Sun, High-Efficiency Violet-Emitting All-Inorganic Perovskite Nanocrystals Enabled by Alkaline-Earth Metal Passivation, Chem. Mater., 2019, 31(11), 3974–3983,  DOI:10.1021/acs.chemmater.9b00442.
146. J.-S. Yao, J. Ge, K.-H. Wang, G. Zhang, B.-S. Zhu, C. Chen, Q. Zhang, Y. Luo, S.-H. Yu and H.-B. Yao, Few-Nanometer-Sized α-CsPbI3 Quantum Dots Enabled by Strontium Substitution and Iodide Passivation for Efficient Red-Light Emitting Diodes, J. Am. Chem. Soc., 2019, 141(5), 2069–2079,  DOI:10.1021/jacs.8b11447.
147. C. Chen, T. Xuan, W. Bai, T. Zhou, F. Huang, A. Xie, L. Wang and R.-J. Xie, Highly Stable CsPbI3:Sr2+ Nanocrystals with near-Unity Quantum Yield Enabling Perovskite Light-Emitting Diodes with an External Quantum Efficiency of 17.1%, Nano Energy, 2021, 85, 106033,  DOI:10.1016/j.nanoen.2021.106033.
148. M. Lu, X. Zhang, Y. Zhang, J. Guo, X. Shen, W. W. Yu and A. L. Rogach, Simultaneous Strontium Doping and Chlorine Surface Passivation Improve Luminescence Intensity and Stability of CsPbI3 Nanocrystals Enabling Efficient Light-Emitting Devices, Adv. Mater., 2018, 30(50), 1804691,  DOI:10.1002/adma.201804691.
149. L. Yang, Q. Shan, S. Zhang, Y. Zhou, Y. Li, Y. Zou and H. Zeng, Improving Anion-Exchange Efficiency and Spectrum Stability of Perovskite Quantum Dots via an Al3+ Bonding-Doping Synergistic Effect, Nanoscale, 2023, 15(12), 5696–5704,  10.1039/D2NR07091J.
150. M. Zhu, L. Qin, Y. Xia, L. Mao, P. Zhao, C. Zhao, Y. Hu, D. Hong, Y. Tian, Z. Tie and Z. Jin, Indium-Doped CsPbI2.5Br0.5 with a Tunable Band Structure and Improved Crystallinity for Thermo-Stable All-Inorganic Perovskite Solar Cells, ACS Appl. Energy Mater., 2023, 6(15), 8237–8244,  DOI:10.1021/acsaem.3c01345.
151. R. Begum, M. R. Parida, A. L. Abdelhady, B. Murali, N. M. Alyami, G. H. Ahmed, M. N. Hedhili, O. M. Bakr and O. F. Mohammed, Engineering Interfacial Charge Transfer in CsPbBr3 Perovskite Nanocrystals by Heterovalent Doping, J. Am. Chem. Soc., 2017, 139(2), 731–737,  DOI:10.1021/jacs.6b09575.
152. T. Oku, Y. Ohishi and A. Suzuki, Effects of Antimony Addition to Perovskite-Type CH3NH3PbI3 Photovoltaic Devices, Chem. Lett., 2016, 45(2), 134–136,  DOI:10.1246/cl.150984.
153. J. Duan, Y. Zhao, X. Yang, Y. Wang, B. He and Q. Tang, Lanthanide Ions Doped CsPbBr3 Halides for HTM-Free 10.14%-Efficiency Inorganic Perovskite Solar Cell with an Ultrahigh Open-Circuit Voltage of 1.594 V, Adv. Energy Mater., 2018, 8(31), 1802346,  DOI:10.1002/aenm.201802346.
154. W. J. Mir, T. Sheikh, H. Arfin, Z. Xia and A. Nag, Lanthanide Doping in Metal Halide Perovskite Nanocrystals: Spectral Shifting, Quantum Cutting and Optoelectronic Applications, NPG Asia Mater., 2020, 12(1), 9,  DOI:10.1038/s41427-019-0192-0.
155. Y. Zhou, J. Chen, O. M. Bakr and H.-T. Sun, Metal-Doped Lead Halide Perovskites: Synthesis, Properties, and Optoelectronic Applications, Chem. Mater., 2018, 30(19), 6589–6613,  DOI:10.1021/acs.chemmater.8b02989.
156. J. T.-W. Wang, Z. Wang, S. Pathak, W. Zhang, D. W. deQuilettes, F. Wisnivesky-Rocca-Rivarola, J. Huang, P. K. Nayak, J. B. Patel, H. A. Mohd Yusof, Y. Vaynzof, R. Zhu, I. Ramirez, J. Zhang, C. Ducati, C. Grovenor, M. B. Johnston, D. S. Ginger, R. J. Nicholas and H. J. Snaith, Efficient Perovskite Solar Cells by Metal Ion Doping, Energy Environ. Sci., 2016, 9(9), 2892–2901,  10.1039/C6EE01969B.
157. W. Lee, S. Hong and S. Kim, Colloidal Synthesis of Lead-Free Silver–Indium Double-Perovskite Cs2AgInCl6 Nanocrystals and Their Doping with Lanthanide Ions, J. Phys. Chem. C, 2019, 123(4), 2665–2672,  DOI:10.1021/acs.jpcc.8b12146.
158. P. Han, W. Zhou, D. Zheng, X. Zhang, C. Li, Q. Kong, S. Yang, R. Lu and K. Han, Lead-Free All-Inorganic Indium Chloride Perovskite Variant Nanocrystals for Efficient Luminescence, Adv. Opt. Mater., 2022, 10(1), 2101344,  DOI:10.1002/adom.202101344.
159. X. Zhou, J. Zhang, X. Tong, Y. Sun, H. Zhang, Y. Min and Y. Qian, Near-Unity Quantum Yield and Superior Stable Indium-Doped CsPbBrxI3−x Perovskite Quantum Dots for Pure Red Light-Emitting Diodes, Adv. Opt. Mater., 2022, 10(2), 2101517,  DOI:10.1002/adom.202101517.
160. P. Sarkar, J. Mazumder, S. K. Tripathy, K. L. Baishnab and G. Palai, Structural, Optoelectronic, and Morphological Study of Indium-Doped Methylammonium Lead Chloride Perovskites, Appl. Phys. A, 2019, 125(8), 580,  DOI:10.1007/s00339-019-2877-1.
161. H.-T. Sun, J. Zhou and J. Qiu, Recent Advances in Bismuth Activated Photonic Materials, Prog. Mater. Sci., 2014, 64, 1–72,  DOI:10.1016/j.pmatsci.2014.02.002.
162. A. L. Abdelhady, M. I. Saidaminov, B. Murali, V. Adinolfi, O. Voznyy, K. Katsiev, E. Alarousu, R. Comin, I. Dursun, L. Sinatra, E. H. Sargent, O. F. Mohammed and O. M. Bakr, Heterovalent Dopant Incorporation for Bandgap and Type Engineering of Perovskite Crystals, J. Phys. Chem. Lett., 2016, 7(2), 295–301,  DOI:10.1021/acs.jpclett.5b02681.
163. Y. Zhou, Z.-J. Yong, W. Zhang, J.-P. Ma, A. Sadhanala, Y.-M. Chen, B.-M. Liu, Y. Zhou, B. Song and H.-T. Sun, Ultra-Broadband Optical Amplification at Telecommunication Wavelengths Achieved by Bismuth-Activated Lead Iodide Perovskites, J. Mater. Chem. C, 2017, 5(10), 2591–2596,  10.1039/C6TC05539G.
164. J. Zhang, M. Shang, P. Wang, X. Huang, J. Xu, Z. Hu, Y. Zhu and L. Han, N-Type Doping and Energy States Tuning in CH3NH3Pb1–xSb2x/3I3 Perovskite Solar Cells, ACS Energy Lett., 2016, 1(3), 535–541,  DOI:10.1021/acsenergylett.6b00241.
165. L. Wang, H. Zhou, J. Hu, B. Huang, M. Sun, B. Dong, G. Zheng, Y. Huang, Y. Chen, L. Li, Z. Xu, N. Li, Z. Liu, Q. Chen, L.-D. Sun and C.-H. Yan, A Eu3+-Eu2+ Ion Redox Shuttle Imparts Operational Durability to Pb-I Perovskite Solar Cells, Science, 2019, 363(6424), 265–270,  DOI:10.1126/science.aau5701.
166. Z.-Y. Chen, N.-Y. Huang and Q. Xu, Metal Halide Perovskite Materials in Photocatalysis: Design Strategies and Applications, Coord. Chem. Rev., 2023, 481, 215031,  DOI:10.1016/j.ccr.2023.215031.
167. N. Fathalizadeh, R. T. Ghahrizjani, S. Shojaei, E. Mohajerani and S. Ahmadi-Kandjani, Enhancing Metal Halide Perovskite LED Performance by Minimizing Ion Migration through the Design of a Mixed 2D(RP+DJ)/3D Active Layer Structure, J. Alloys Compd., 2025, 1010, 177813,  DOI:10.1016/j.jallcom.2024.177813.

---