Engineering indium phosphide quantum dots for solar-driven energy conversion applications

Abstract

Colloidal indium phosphide (InP) quantum dots (QDs) have emerged as a compelling class of heavy metal-free nanomaterials due to their low toxicity and size-tunable optoelectronic properties, showing great potential in solar-driven energy conversion applications. Here, a variety of synthetic techniques for preparing high-quality InP QDs, including hot-injection, heat-up, cluster-mediated growth, and cation exchange, are thoroughly reviewed. To realize enhanced photocatalytic (PC) and photoelectrochemical (PEC) performance, diverse strategies such as core/shell engineering, hybrid ligand modification and elemental doping of InP QDs are discussed in detail, which are beneficial to build various efficient QDs-based systems for hydrogen evolution, CO₂ reduction, ammonia synthesis, and H₂O₂ production. Moreover, the main challenges and future research directions of InP QDs are briefly proposed, providing guidelines to achieve future low-cost, eco-friendly, scalable and high-efficiency QDs-based solar energy conversion technologies.

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Hongyang Zhao

Hongyang Zhao is currently a lector at Mianyang Normal University (China). He obtained his MS degree in Chemistry (2020) from Chongqing University and PhD degree in Materials Science and Engineering (2024) from University of Electronic Science and Technology of China (China). His research interests focus on the rational design and synthesis of materials for solar-driven energy conversion applications.

Zhenwei Tang

Zhenwei Tang is pursuing a BE degree in Chemistry at School of Chemistry and Materials Engineering, Mianyang Normal University (China), under the supervision of Dr Zhao. Her research interests focus on the rational design and synthesis of materials for solar-driven energy conversion applications.

Shuya Cui

Shuya Cui is currently a professor at Mianyang Normal University (China). She obtained her BS degree in Lanzhou University (1998), MS degree in Organic Chemistry from Lanzhou University (2001) and PhD degree in Analytical Chemistry (2004) from Lanzhou University (China). Her research interests focus on Organic photoelectric materials.

Lirong Yang

Lirong Yang is currently an associate professor at Mianyang Normal University (China). She obtained a BE degree in Xihua University (2009) and PhD degree in Materials Science and Engineering (2022) from China Academy of Engineering Physics. Her research interests focus on materials, physics and chemistry.

Xinjie Xiang

Xinjie Xiang is pursuing a BE degree in Chemistry at the School of Chemistry and Materials Engineering, Mianyang Normal University (China), under the supervision of Dr Zhao. Her research interests focus on the rational design and synthesis of materials for solar-driven energy conversion applications.

Jianni Bai

Jianni Bai is pursuing a MS degree in Electronic Science and Technology at the Institute of Fundamental and Frontier Sciences, University of Electronic Science and Technology of China (China), under the supervision of Professor Xin Tong. Her research interests focus on the optoelectronic applications of colloidal quantum dots.

Jingying Luo

Jingying Luo obtained her BE degree in Materials Science and Engineering from Chongqing University (China) in 2016, and MS degree in Materials Engineering from Xidian University (China) in 2021. She is currently a PhD candidate at the Institute of Fundamental and Frontier Science, University of Electronic Science and Technology of China (China), under the supervision of Prof. Zhiming Wang. Her current research mainly focuses on the synthesis of colloidal quantum dots and their applications in photodetectors.

Zhuojian Li

Zhuojian Li received his BS degree in Materials Science and Engineering from Southwest Jiaotong University in 2022. He is currently a PhD candidate at the Institute of Fundamental and Frontier Science, University of Electronic Science and Technology of China, under the supervision of Prof. Xin Tong. His research interests focus on the synthesis of colloidal quantum dots for photoelectric conversion applications.

Xin Li

Xin Li is currently a lector at Panzhihua University. He obtained his BE degree in Electronic Science and Technology (2019) and PhD degree in Materials Science and Engineering (2024) from the University of Electronic Science and Technology of China (China). His research interests focus on rational design and synthesis of colloidal quantum dots for photoelectric conversion devices.

Guoqi Xiang

Guoqi Xiang is currently a professor at Panzhihua University. He obtained his PhD degree in Mechatronics Engineering (2010) from the University of Electronic Science and Technology of China (China). His main research areas are multidisciplinary design optimization, intelligent electromechanical systems, and data mining.

Wuyang Ren

Wuyang Ren is currently an associate professor at the University of Electronic Science and Technology of China. He obtained his BE degree in Electronic Science and Technology (2013) and PhD degree in Materials Science and Engineering (2019) from the University of Electronic Science and Technology of China (China). His research interests focus on materials physics and optoelectronics.

Xin Tong

Xin Tong is currently a professor at the University of Electronic Science and Technology of China. He obtained his BE degree in Electronic Science and Technology (2014) and PhD degree in Materials Science and Engineering (2018) from the University of Electronic Science and Technology of China (China). His research interests focus on the rational design and synthesis of colloidal quantum dots for optoelectronic applications.

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1. Introduction

Semiconductor quantum dots (QDs) are nanocrystalline materials characterized by quantum confinement effects, which confer size-tunable optoelectronic properties with considerable potential for various solar energy conversion applications.^1–3 For instance, CdS QDs were rationally engineered for photocatalytic (PC) CO₂ reduction, achieving outstanding performance superior to most state-of-the-art PC systems even without sacrificial agents.⁴ Similarly, CdSe-based core/shell QDs have been demonstrated as efficient photocatalysts for H₂ generation with exceptional efficiency and operational stability.⁵ In photoelectrochemical (PEC) systems, PbS QDs were also employed to enhance the power conversion efficiency, notably enabling H₂ evolution from an aqueous Na₂S solution with a peak external quantum efficiency (EQE) exceeding 100%.⁶ Despite their high performance, conventional cadmium (Cd)- and lead (Pb)-based QDs face restrictions under regulations such as the restriction of hazardous substances (RoHS) directive due to their toxicity, thus limiting their commercial viability.^7–9 In this case, heavy metal-free QDs have attracted increasing attention as environmentally benign alternatives for sustainable optoelectronics.

Among them, indium phosphide (InP) QDs have emerged as a leading candidate for solar energy conversion owing to their low toxicity, favorable bulk bandgap (∼1.35 eV), large exciton Bohr radius (∼10 nm), and tunable absorption across the visible to near-infrared range.^10–13 As shown in Fig. 1, numerous scientific studies associated with InP QDs have been increasingly published since 1994,¹⁴ reflecting their growing significance in this field. Their covalent crystal structure also contributes to enhanced chemical stability compared to ionic II–VI QDs.^15,16 However, early synthesis of high-quality InP QDs was hindered by the high In–P bond dissociation energy and challenges in controlling nucleation and surface defects.^17–19 Recent progress in synthetic methodologies has alleviated these issues. Specifically, The hot-injection technique enabled rapid separation of nucleation and growth phases to improve the size uniformity;^20–24 cation exchange provides a pathway to form In–P bonds under milder conditions to reduce defect formation;^25–28 and continuous-flow synthesis ensures highly reproducible reaction environments, facilitating scalable production of high-quality InP QDs with enhanced optical properties.^29–31 Furthermore, sophisticated core/shell designs such as InP/ZnSe/ZnS have achieved photoluminescence quantum yields (PLQY, the ratio of the emitted and absorbed photons) exceeding 90%, rivaling those of Cd-based QDs while maintaining RoHS compliance.¹⁸

Fig. 1 Timeline and number of publications on the synthesis and solar energy conversion applications of InP QDs.

Advances in the material perspective of InP QDs have facilitated their applications in a variety of solar-driven processes, including PC hydrogen evolution, CO₂ reduction, ammonia synthesis and H₂O₂ generation. Through tailored surface chemistry and hybrid structures, InP QDs have demonstrated remarkable stability and activity in solar-driven energy conversion systems, such as continuous CO₂-to-CO conversion over 420 hours.³² Nevertheless, issues including charge recombination, limited large-scale production, and long-term operational stability remain obstacles to practical deployment.

Although several reviews have summarized the synthesis and optical properties of InP QDs, a comprehensive overview focusing on their solar energy conversion applications, spanning materials design, mechanistic insights, and device integration, is still lacking.^33–35 This review summarizes recent developments in the synthesis, property modulation and PC/PEC applications of InP QDs, offering a forward-looking perspective on overcoming key barriers to commercialization.^15,36–41 By linking materials innovation with energy-oriented functionality, this review aims to guide the development of efficient, stable, and scalable heavy metal-free QDs technologies for sustainable solar energy conversion.

2. Synthetic strategies

The pursuit of high-quality InP QDs depends on sophisticated synthetic methodologies that govern precursor reactivity, nucleation kinetics, and crystal growth within high-temperature coordinating solvents.^42–45 Two principal strategies have emerged as the foundation of contemporary synthesis: (i) the hot-injection method, which facilitates abrupt nucleation through rapid introduction of precursors into a heated reaction medium; (ii) the heat-up approach that enables more scalable production via controlled thermal ramping.^46–48 Beyond these core techniques, advanced procedures such as cluster growth and cation exchange have further enriched the synthetic landscape, allowing precise architectural and compositional control over heterostructures and alloyed QDs.^21,46 These synthetic methods could affect the size distribution, crystallinity, and optoelectronic properties of InP QDs, which are important for optimizing their performance in solar energy conversion applications.⁴⁹

2.1 Hot-injection

The hot-injection is a typical technique for synthesizing high-quality InP QDs, providing precise control over nucleation and growth through rapid introduction of precursors into a heated reaction medium.^8,35 This process relies on instantaneous supersaturation to achieve homogeneous nucleation, which is critical for obtaining QDs with narrow size distribution and high crystallinity.^23,50,51 Although hot-injection technique was originally developed for II–VI QDs, its adaptation to III–V QD materials required in-depth reengineering of precursor chemistry and reaction conditions to address challenges such as uncontrolled phosphorus reactivity and interfacial oxidation.^52,53 Continued refinements in injection strategies, including sequential and co-injection protocols, have improved the reproducibility and scalability of InP QDs with tailored optoelectronic properties.^54,55

As illustrated in Fig. 2(a), the hot-injection synthesis of InP QDs typically proceeds through three stages: (i) an indium precursor solution was first introduced into a hot coordinating solvent to precondition the system; (ii) the subsequent rapid injection of the phosphorus precursor induced a sharp increase in monomer concentration to trigger homogeneous nucleation; (iii) a gradual decrease in monomer concentration facilitated the diffusion-controlled Ostwald ripening, thus yielding monodisperse InP QDs.^35,56 This schematic highlights how subtle variations in injection timing and sequencing profoundly influence the nucleation kinetics and final particle characteristics of QDs.

Fig. 2 Synthesis and optical properties of InP QDs prepared by hot-injection and heat-up methods. (a) Comparison of the hot-injection and heat-up synthesis processes for colloidal QDs. (b) Optical images of InP QDs prepared via different [In] precursor (InCl, InBr, and InI) and corresponding evolution of PL and ultraviolet-visible (UV-vis) absorption spectra. Reproduced with permission.²⁰ Copyright 2023, American Chemical Society. Absorption (solid) and PL (dashed) spectra of (c) heat-up synthesized and (d) hot-injection synthesized InP QDs before (black) and after (green) InF₃ treatment. (e) PLQY and (f) FWHM values of four types of InP QDs synthesized using different approaches. Reproduced with permission.⁷⁰ Copyright 2024, American Chemical Society.

The development of more sophisticated precursor design and reaction engineering has yielded hot-injection-synthesized InP QDs with substantially improved quality. While tris(trimethylsilyl)phosphine (P(TMS)₃) remains widely used, less hazardous alternatives such as tris(diethylamino)phosphine (P(NEt₂)₃) were increasingly employed to improve the size distribution and batch reproducibility.^20,23,35,57 Ligands, including fatty acids and long-chain amines, serve not only as colloidal stabilizers but also as reaction rate moderators by influencing precursor decomposition kinetics.⁵⁸ The introduction of zinc halides as co-precursors has proven effectiveness in enhancing the crystallinity and PLQY by reducing the surface trap states of InP QDs.^59,60 By effectively optimizing the reaction parameters, such as injection temperatures between 230–260 °C and growth durations within two minutes, spectral tunability across the visible range and PLQY exceeding 80% could be realized.^56,61,62

Fig. 2(b) illustrated an innovative hot-injection synthesis route for InP QDs utilizing monovalent indium halides (InX, X = Cl, Br, I).²⁰ This approach employed In(I) species as dual-functional precursors, which serve simultaneously as indium sources and reducing agents for aminophosphines. It represented a notable advance over conventional In(III)-based methods because it could eliminate the requirement of zinc additives during synthesis, a common source of structural defects and emission line broadening.¹² Such synthesis technique produced well-defined tetrahedral InP QDs with edge lengths exceeding 10 nm and narrow size distribution, reflecting improved control over nanocrystal morphology and uniformity. Generally, halide identity could critically modulate the optical characteristics of InP QDs, enabling the tuning of the first excitonic absorption peaks across the visible spectrum (from 450 nm to 700 nm), with correlated shifts in the PL emission peaks. The resulting InP QDs displayed exceptionally narrow PL linewidths, as low as 112 meV at 728 nm, which indicated their highly effective surface passivation and strongly suppressed defect-associated recombination.²⁰ The different spectral evolution behaviors observed in QD synthesis using diverse halide systems further implied the unique reaction kinetics and surface stabilization pathways, providing essential insights for precursor choice in the hot-injection synthesis of high-quality III–V QDs.^63,64

2.2 Heat-up

The heat-up synthesis of colloidal InP QDs begins with a homogeneous precursor mixture at room temperature, followed by a precisely controlled temperature ramping process (Fig. 2(a)).^7,65–67 Unlike hot-injection method requiring rapid injection and abrupt thermal quenching, this synthetic approach avoids stringent kinetic control and subjects the reaction system to continuous thermodynamic changes,⁶⁸ which often leads to a overlap of nucleation and growth processes.⁶⁹ Therefore, achieving temporal separation between these stages demands careful optimization of parameters such as precursor-to-ligand molar ratios, maximum reaction temperature, and heating rate profiles.⁵⁶

Recent studies by Reiss and co-workers have shown that moderate nucleation kinetics under heat-up conditions yielded improved size uniformity of InP QDs, as evidenced by a sharper excitonic absorption feature compared to the hot-injection synthesized InP QDs (Fig. 2(c) and (d), black curves).⁷⁰ Their work identified heating rate as a vital factor to influence the nanocrystal quality, with optimal values between 5–10 °C min⁻¹ markedly reducing the overlap between nucleation and growth. This controlled synthetic method contributed to a higher PLQY, reaching up to 93% after InF₃ treatment in heat-up synthesized QDs (Fig. 2(c), green curve), surpassing the maximum PLQY of 71% obtained via hot-injection under comparable conditions (Fig. 2(d), green curve).⁷⁰

Building upon the superior size uniformity achieved through moderate nucleation kinetics, the heat-up method further demonstrates its advantage in radiative efficiency. As corroborated by the statistical data in Fig. 2(e), InP QDs prepared via the heat-up method achieve far higher PLQY than those from the hot-injection route across a range of post-synthetic treatments. The insight from this comparison is that the superior PLQY of the heat-up QDs does not result from improved size distribution, as evidenced by their comparable full width at half maximum (FWHM, a measure of the width of a peak or distribution at half of its maximum amplitude) values to the hot-injection samples (Fig. 2(f)). Instead, the higher radiative efficiency is originated from an intrinsic superiority in nanocrystal quality that fewer structural defects and non-radiative trap states afforded by the more controlled, moderate nucleation kinetics of the heat-up process. This finding solidified the argument that the optimized heating profile was a pivotal synthetic parameter, which concurrently enhanced the size uniformity and suppressed the defect formation to yield highly luminescent InP QDs.

2.3 Cluster-based synthesis

The formation of InP QDs through magic-sized clusters (MSCs) offers a sophisticated bottom-up pathway that connects molecular precursors to well-defined nanocrystals.^71–74 These ∼2 nm intermediates, known for their atomically precise structures, act as key templates for QDs growth.⁷⁵ Recent studies by Lee et al. have shown that additives such as ZnCl₂ and tri-n-octylphosphine can be used to controllably destabilize InP MSCs, thus leading to the formation of monodisperse QDs with high PLQY (Fig. 3(a)).⁷⁶ Herein, the zinc halide promoted the surface ligand exchange, while the tri-n-octylphosphine disrupted the indium carboxylate coordination, collectively facilitating the transformation of MSCs into quantum-confined nanocrystals. As demonstrated by Li et al., the temporal separation of MSC formation and QD growth stages is essential, since it can directly convert the discrete InP MSCs into QD cores at 150 °C (Fig. 3(b) and (c)).⁷⁷ Such controllable pathway enables the synthesis of blue-emitting InP QDs with narrow size distribution, underscoring the utility of MSCs in modulating nucleation.

Fig. 3 Cluster-mediated synthesis and transformation mechanism of InP-based QDs: (a) nucleation and growth mechanism illustrating MSCs destabilization during In(Zn)P QD synthesis. Adapted with permission.⁷⁶ Copyright 2023 American Chemical Society. (b), (c) Schematic of MSC-derived InP QD synthesis pathway along with corresponding TEM images and size distribution histogram. Adapted with permission.⁷⁷ Copyright 2022 Elsevier. (d) The proposed pathways for InP QDs formation from different MSCs, (e) time-dependent UV-vis absorption spectra showing the conversion of In₃₇P₂₀ clusters into InP QDs after the introduction of P(SiMe₃)₃, (f) kinetic traces of absorbance at 500 nm following the addition of 10 equivalents of P(SiMe₃)₃ to each cluster solution. (d)–(f) adapted with permission.⁷⁸ Copyright 2024 American Chemical Society. Synthesis and structural evolution of InP QDs via cation exchange: (g) schematic for preparing water-soluble w-InP QDs from Cu_3−xP templates by cation exchange, (h) TEM images of w-InP QDs with different sizes (scale bar: 20 nm). (g), (h) adapted with permission.²⁶ Copyright 2024 American Chemical Society. (i) Reaction pathway from Cu⁰ to Cu_3−xP, followed by the In/Zn-halide cation exchange and NOBF₄ treatment. (j) high-angle annular dark-field and scanning-transmission electron microscopy (HAADF-STEM) images and energy-dispersive X-ray spectroscopy (EDS) mapping showing the phase evolution from Cu⁰ to w-InP QDs (scale bar: 5 nm). (i), (j) adapted with permission.²⁷ Copyright 2023 American Chemical Society.

Structural studies of MSC intermediates have provided critical mechanistic insights into the formation processes of InP QDs. The In₃₇P₂₀(O₂CR)₅₁ cluster has been identified as a key isolable intermediate whose reactivity dictates the subsequent growth kinetics (Fig. 3(d)).⁷⁸ Ligand engineering, particularly through substituted phenylacetate derivatives, has demonstrated how steric effects precisely modulated the cluster stability. For instance, meta-substituents could enhance the phosphine accessibility to cluster core, while para-substituents introduced kinetic barriers that inhibited the core dissolution.⁷⁹ This ligand-mediated control over cluster stability not only regulated the nucleation timeline but also enabled the isolation and crystallographic determination of an earlier In₂₆P₁₃(O₂CR)₃₉ intermediate, offering atomic-level insight into III–V cluster evolution. These findings established a clear structure and reactivity relationship that directly links ligand engineering to cluster-based synthesis pathways, thereby providing a rational framework for controlling the formation of high-quality InP QDs through intermediate stabilization and reaction kinetics modulation.

Kinetic analyses of the cluster-to-QDs transformation can provide a quantitative perspective on the growth mechanism of InP QDs. As tracked via the absorbance changes at 500 nm (Fig. 3(e) and (f)), the real-time monitoring of the reaction between In₃₇P₂₀ MSCs and P(SiMe₃)₃ in toluene reveals distinct conversion stages,⁷⁸ showing the rapid emergence of excitonic features following cluster dissolution that confirmed the MSC-derived nucleation. In parallel, the temperature-dependent studies highlighted the influence of thermal barriers on reaction kinetics. Specifically, the elevated temperatures lowered the activation energy for cluster decomposition, accelerating the release of monomeric species as seeds for QDs growth. This thermal modulation directly governed the rate of cluster consumption and the subsequent nucleation burst, thereby enabling precise control over the size distribution and final quality of InP QDs. These kinetic insights established a direct link between cluster-based precursor design and the rational synthesis of monodisperse QDs.

2.4 Cation exchange

The cation exchange strategy has emerged as a transformative pathway for synthesizing InP QDs, enabling a structural modification with preserved original nanocrystal framework.^80–82 This process relies on selective cation substitution within preformed templates through controlled solvation thermodynamics and Lewis acid–base interactions.⁸³ Unlike direct synthesis methods, cation exchange maintains the initial anion sublattice due to the low mobility of phosphorus atoms, allowing the fine regulation of QDs morphology and crystallinity.⁸⁴ As demonstrated by the production of monodisperse wurtzite-phase InP (w-InP) QDs with well-defined optical properties, this strategy represented a viable alternative to conventional InP QD synthesis.⁸⁵

Banin and coworkers illustrated the complete transformation from Cu_3−xP nanocrystals to luminescent w-InP QDs,²⁶ wherein the reaction began with Cu-to-In cation exchange to yield initially non-emissive w-InP QDs with broad absorption profiles (Fig. 3(g)). Subsequent treatment with nitrosyl tetrafluoroborate (NOBF₄) was essential to activate the PL by removing residual copper species and tuning the surface stoichiometry. The transmission electron microscopy (TEM) images of QDs in Fig. 3(h) demonstrated the size control through precursor selection and etching duration, in which the copper tartrate templates produced larger QDs (5.9–6.9 nm), while those derived from copper acetate yielded smaller sized QDs (4.5–5.0 nm), illustrating the role of different Cu-based templates in achieving controllable sizes of InP QDs.

Further mechanistic insight into the multistep synthesis was provided by the same group through systematic analysis.²⁷ Fig. 3(i) illustrated the initial formation of Cu⁰ nanocrystals with phosphorus precursors, with the ensuing reaction pathway dictated by the copper precursor's thermal stability. Specifically, stable copper halides directly reacted with phosphorus sources to form Cu_3−xP above 260 °C, whereas less stable copper oxyanions first generated intermediate Cu⁰ nanocrystals, which were subsequently converted into Cu_3−xP at elevated temperatures. This precursor-dependent divergence underscored the important role of precursor decomposition kinetics in directing the phase evolution pathway. Additionally, Fig. 3(j) tracked the transformation processes from Cu⁰ nanocrystals with surface phosphorus through mixed-phase intermediates to the final Cu_3−xP products. When integrated with subsequent Cu-to-In cation exchange and NOBF₄ treatment, this well-defined reaction process has provided a reproducible and controllable route to synthesize high-quality InP QDs with tunable optoelectronic properties.

3. Modulation of optoelectronic properties

The optoelectronic properties of QDs are fundamentally governed by the efficiency of radiative recombination.⁸ However, InP bare-core QDs are particularly susceptible to nonradiative decay pathways due to their high surface-to-volume ratio and inherent lattice instability.⁸⁶ Surface atoms, which constitute an important fraction of the total atoms in nanoscale systems, could create unsaturated bonds that act as trap states within the bandgap.⁸⁷ These defect states readily capture the photogenerated charge carriers, promoting nonradiative Auger recombination or energy transfer to the environment for severely quenched PL emission,³⁸ thus resulting in characteristically low PLQY (<10%) and poor photostability for bare InP core QDs.²³

3.1 Core–shell structure

Given the aforementioned limitations of bare InP QDs, core/shell structures have been employed to achieve effective surface defect passivation and enhanced exciton confinement. Building on this strategy, the gradient core/shell architecture has emerged as a major advance, offering considerable control over both the PLQY and emission linewidths of QDs for optoelectronic applications.^48,86,88,89 By replacing abrupt heterointerfaces with compositionally graded shells, this approach could mitigate the lattice strain, suppress the non-radiative recombination and improve the exciton confinement of QDs.^7,15,77 Thanks to recent developments in precursor chemistry, particularly the use of alkylsilylamine-based aminophosphines, the synthesis of InP-based gradient core/shell QDs with enhanced PLQY and narrow emission profiles has been achieved.^90–92 Furthermore, precise control over multiple shell parameters, including thickness, chemical composition, and crystalline phase, is essential for fine-tuning charge carrier dynamics and realizing substantially improved photostability in these gradient core–shell structured QDs.^93–96

A notable study by Sang Man Koo et al. demonstrated the benefits of incorporating a ZnSeS gradient interlayer in InP-based core/shell QD systems.⁹¹ Fig. 4(a) schematically depicted the graded shell architecture of InP/ZnSeS/ZnS QDs, which is designed to mitigate the lattice mismatch between the core and the outer shell. Corresponding spectroscopic data in Fig. 4(b) confirmed a high monodispersity of the initial InP cores, as evidenced by a sharp excitonic absorption peak. Following the shell growth, the absorption and emission spectra of the InP/ZnSeS/ZnS QDs are redshifted. More importantly, the marked narrowing of the emission peak and the enhancement in PL intensity provided direct evidences for effective surface passivation and a reduction in defect states. A narrow emission profile with a FWHM of 48 nm further reflected the gradient shell's effectiveness in suppressing inhomogeneous broadening of QDs.⁹⁰

Fig. 4 Structural and optoelectronic properties of gradient InP-based core/shell QDs. (a) Schematic of the graded shell architecture in InP/ZnSeS/ZnS QDs and (b) corresponding absorption and UV-vis absorption spectra highlighting the narrow emission. (a), (b) Reproduced with permission.⁹¹ Copyright 2025 Wiley-VCH. (c) Synthesis pathway for WZ-phase ZnSe shells on InP core QDs. (d) Calculated exciton energy shift as a function of QD volume for InP QDs with ZB (gray) and WZ (red) ZnSe shell. (e) Band alignment diagrams comparing the ZB and WZ InP/ZnSe QDs and (f) UV-vis absorption and PL spectra during shell growth. (c)–(f) Reproduced with permission.⁹⁷ Copyright 2025 American Chemical Society.

In another work, Li et al. investigated the influence of shell crystal phase on the optoelectronic properties of InP core–shell QDs.⁹⁷ Through a phase-controlled synthesis strategy detailed in Fig. 4(c), this group achieved the growth of a wurtzite (WZ) ZnSe shell on InP core QDs. It is indicated that this shell with WZ phase confers a stronger quantum confinement compared to its zinc blende (ZB) counterpart. The proposed mechanism attributes this effect to the distinct electronic structure inherent to the WZ lattice, which likely modifies the confinement potential landscape by creating a deeper potential well for charge carriers at the core–shell heterojunction. As shown in Fig. 4(d), the calculated exciton energy results revealed a redshift in exciton energy for InP/ZnSe-WZ core–shell QDs compared to their ZB counterparts. This was primarily attributed to the larger conduction band offset in the WZ structured core–shell QDs, which led to a higher degree of carrier localization and a more pronounced redshift in emission energy. The energy level alignment diagrams in Fig. 4(e) further illustrated a smaller conduction band offset in the ZB structured QDs, which facilitated the delocalization of the electron wave function into the shell. UV-vis absorption and PL spectra of these InP/ZnSe-WZ core/shell QDs revealed spectral shifts at different stages of the shell growth process, as shown in Fig. 4(f). As the shell thickness increased, both absorption and PL spectra exhibited a progressive redshift and ultimately achieved a high PLQY of 92%. This observation was consistent with the enhanced carrier localization effect due to the coating of a ZnSe shell with WZ phase, further confirming the successful growth of a high-quality crystalline shell under the optimized low-temperature conditions implemented to preserve the desired crystal structure.

Based on the fundamental advances of gradient core/shell architectures, the next critical step is to further optimize the optical and structural properties of InP QDs through precise control of shell composition.^24,98 The introduction of alloyed shells (e.g., ZnSe_xS_1−x) is able to enhance the confinement of photogenerated charge carriers, reduce the lattice strain, and suppress the defect-mediated non-radiative recombination.^88,89 Compositional grading within the shell further promotes the exciton localization and enables spectral tunability across the visible range, underscoring the potential of InP QDs for high-performance optoelectronic devices.⁹⁹

For example, Zhao et al. investigated the influence of alloyed inner shells on the optical properties of InP QDs.⁹³ Fig. 5(a) illustrated the ZnSe_xS_1−x interfacial layer in a InP/ZnS core–shell QD system, which is a key structural design employed to alleviate the lattice mismatch between the InP core and the outer ZnS shell for reduced interfacial defects. As exhibited in Fig. 5(b), the X-ray diffraction (XRD) was used to investigate the formation of phase-pure InP/ZnSe_xS_1−x QDs across different compositions formed by tuning the Se/S precursor ratio during the inner shell growth. A key observation was that the diffraction peaks gradually shifted with increased Se/S ratio. For the InP/ZnSe_0.7S_0.3/ZnS structure, the peaks reside between those of the core and the ultimate ZnS shell, demonstrating the role of this intermediate layer in mitigating lattice mismatch and promoting coherent shell growth. Increasing the Se contents induced a redshift in both the first excitonic absorption peak (from 475 nm to 505 nm) and the PL peak (from 508 nm to 535 nm), as shown in Fig. 5(c) and (d). This red-shift is derived from a reduced conduction band offset at the InP/ZnSe_xS_1−x interface, thus narrowing the effective band gap and enhancing the electron delocalization. A maximum PLQY of 97% and a FWHM of 35 nm were achieved at x = 0.7 (Fig. 5(d) and (e)), with the enhanced brightness visually confirmed by the photographs in Fig. 5(f).

Fig. 5 Composition-dependent optical and structural properties of InP-based core–shell QDs with engineered inner shells. (a) Schematic of the InP/ZnSe_xS_1−x/ZnS structured QDs. (b) XRD patterns of composition-dependent QDs showing lattice parameter evolution. (c), (d) Absorption and PL spectra of InP/ZnSe_xS_1−x/ZnS QDs with varying Se/S ratios, (e) Correlation among FWHM, PL peak position and PLQY and (f) digital photographs of QD solutions under UV illumination. (a)–(f) Reproduced with permission.⁹³ Copyright 2022 Springer Nature. (g) Shell growth pathways using single S and dual Se/S precursors for InP/ZnSe/ZnSeS QDs. (h) Size distribution histograms and (i) normalized PL and absorption spectra of the resulting QDs. (g)–(i) Reproduced with permission.³⁹ Copyright 2025 Wiley-VCH. (j) Linear correlation between the injected and incorporated sulfur in InP/ZnSe/ZnS QDs and (k) their tunable PL emission covering the visible spectrum. (j), (k) Reproduced with permission.¹⁰⁰ Copyright 2022 American Chemical Society.

Wu et al. compared the single sulfur precursor and dual selenium/sulfur precursor shell growth routes for InP/ZnSe/ZnS_thick and InP/ZnSe/ZnSeS/ZnS_thick QDs.³⁹ Fig. 5(g) illustrated the two synthesis pathways, showing that the extended ZnS shell growth for 12 hours could yield QDs exceeding 20 nm in diameter. Incorporating the selenium near the core region reduced the lattice strain, enabling a thicker shell deposition even at identical Se/S ratios (25/75) and growth durations (Fig. 5(h)). Although both methods produced QDs emitting at 630 nm (Fig. 5(i)), the dual-precursor approach enhanced the optical absorption at the higher energy range, indicating the improved shell quality and a lower defect density. These findings demonstrated that the precursor selection and spatial distribution strongly influenced the shell growth kinetics and QDs morphology. Similarly, Zeger Hens and colleagues demonstrated that the tailored Zn(Se, S) inner shells on InP core QDs enabled broad spectral coverage while reducing inhomogeneous broadening induced by lattice mismatch.¹⁰⁰ Fig. 5(j) showed the elemental analysis from EDS, which revealed that the resulting QDs contained sulfur in proportion to the amount of added tri-n-octylphosphine sulfur (TOP-S). As a result, a tunable PL emission of these QDs across the visible spectrum was realized, as shown in Fig. 5(k).

3.2 Ligand engineering

Ligand engineering is also a strategy to optimize the properties of InP QDs. Among various options, short-chain ligands represent a notable advancement in the surface engineering of InP QDs, providing superior defect passivation and enhanced interfacial charge transport relative to traditional long-chain ligands.^86,101–103 Moreover, their compact molecular structure enables a dense binding to the surface sites, thus markedly improving the operational stability.^104,105

Tang et al. demonstrated the effectiveness of cysteamine (CTA) as a short-chain ligand on InP/ZnSe/ZnS QDs.¹⁰⁶ As shown in Fig. 6(a), CTA facilitated a strong surface coordination to cause a substantial increase in PL intensity (Fig. 6(b)) and a longer radiative recombination lifetime (Fig. 6(c)). Furthermore, introducing a small amount of CTA into the QD solution increased the proportion of radiative recombination (Fig. 6(d)). The observed improvements in PL intensity and radiative recombination efficiency confirmed that CTA effectively passivated the surface defects of QDs and enhanced the radiative recombination rate of intrinsic excitons. In a parallel strategy, Himchan Cho et al. employed molecular metal chalcogenide complexes (MCCs) as multifunctional ligands that improved both the exciton dissociation and the colloidal stability in aqueous environments (Fig. 6(e)).¹⁰⁷ Retention of the optical properties after ligand exchange (Fig. 6(f)) and a pronounced negative shift in zeta potential (Fig. 6(g)) confirmed the effective surface modification and increased dispersibility of as-prepared MCC-functionalized InP/ZnSe/ZnS QDs (MCC-InP QDs).

Fig. 6 Ligand engineering of InP-based QDs. (a) Schematic of InP/ZnSe/ZnS QDs with CTA ligand and relevant defect passivation mechanism. (b) Steady-state PL spectra and (c) time-resolved PL decay curves of QD and QD-CTA films. (d) Time-resolved PL decay curves of various QD solutions. (a)–(d) Reproduced with permission.¹⁰⁶ Copyright 2024 American Chemical Society. (e) Schematic of MCC-InP QDs. (f) UV-vis absorption and PL spectra of InP/ZnSe/ZnS QDs. (g) Zeta potential of pristine and MCC-InP QDs. (e)–(g) Reproduced with permission.¹⁰⁷ Copyright 2025 Wiley-VCH.

Hybrid ligand engineering has also emerged as a promising strategy for enhancing the colloidal stability and optoelectronic properties of InP QDs.¹⁰⁸ By combining the ligands with complementary functionalities, this approach could effectively passivate the surface defects and suppress the fluorescence blinking.^24,109,110 For instance, the photobleaching and emission intermittency of InP QDs are still primary challenges for their applications in bioimaging and highly sensitive single-molecule detection. Regarding this issue, Li et al. compared the optical properties of three types of water-soluble InP/ZnSe/ZnS QDs at the single-particle level, which were modified with either mercaptopropionic acid (MPA), mercaptoundecanoic acid (MUA), or a mixture of both ligands (Fig. 7(a)).¹¹¹ Fig. 7(b)–(d) showed the typical PL intensity trajectories of the three types of QDs. QDs with only MPA or MUA ligands showing frequent intensity fluctuations, indicating a pronounced emission intermittency. In contrast, QD-MPA-MUA with mixed ligands exhibited suppressed blinking and maintained a stable bright on state (Fig. 7(d) and (g)). The on-state probability refers to the percentage of time a QD remains bright under continuous excitation. Statistical analysis of 100 individual QDs revealed that the mixed ligand system achieved an on-state fraction of 95.2%, which was notably higher than the 63.7% for QD-MPA and 70.1% for QD-MUA (Fig. 7(e) and (f)). The combination of short-chain MPA and long-chain MUA ligands enabled a stable surface coverage, effectively passivating the defect sites responsible for Auger recombination and blinking. Such synergistic passivation not only enhanced the photostability but also improved the charge balance, which led to the observed high on-state probability.

Fig. 7 Hybrid ligand passivation strategies for InP QDs. (a) Schematic of QDs functionalized with MPA, MUA, and MPA–MUA hybrid ligands (left) and their aqueous dispersion stability (right). (b)–(d) Single-QD PL trajectories and (e)–(g) corresponding on-state probability statistics demonstrating blinking suppression in MPA-MUA QD systems. (a)–(g) Reproduced with permission.¹¹¹ Copyright 2025 American Chemical Society. (h) A proposed mechanism of dilution-induced ligand desorption and (i)–(k) concentration-dependent PL properties highlighting the ligand stabilization. (h)–(k) Reproduced with permission.¹¹² Copyright 2025 American Chemical Society. (l) Synthesis route and (m) PL enhancement of HF-pyridine treated QDs. (l)–(m) Reproduced with permission.¹¹³ Copyright 2025 American Chemical Society. (n) Schematic of CLIP patterning using photocleavable BNA ligands and (o) retained optical properties after ligand exchange. (n)–(o) Reproduced with permission.¹¹⁵ Copyright 2025 American Chemical Society.

To unravel the stability mechanisms of hybrid ligand in InP QD systems, Hou's group explored ligand adsorption–desorption thermodynamics through controlled dilution experiments (Fig. 7(h)–(k)).¹¹² Fig. 7(h) illustrated that InP QDs diluted in pure water underwent substantial ligand desorption, whereas the pre-addition of extra ligands preserved the surface coverage. In Fig. 7(i), 100-fold dilution introduced a fast decay component (∼5 ns) and reduced the average PL lifetime from 28 ns to 16 ns, indicating the enhanced non-radiative recombination. Fig. 7(j)–(k) showed that pre-adding MPA (0–20 mM) suppressed the fast decay component and restored the PLQY from 42% to 92% under dilution. These findings verified the importance of ligand pre-equilibrium for maintaining optical performance under dilute conditions.

Beyond the scope of conventional ligand strategies (Fig. 7(h)–(k)), Yang's group reported a dual strategy of HF etching and pyridine ligand exchange for synergistic passivation of InP-based core–shell QDs (Fig. 7(l)),¹¹³ wherein the HF purified the surface and the pyridine ensured strong capping to synergistically produce a dramatic PL enhancement and a pronounced blueshift (Fig. 7(m)). It is demonstrated that the combined chemical and ligand modifications could rival advanced ligand engineering in boosting the optical properties of InP-based QDs.

The cleavable ligand-induced photolithography (CLIP) strategy is fundamentally connected to the performance of optoelectronic devices including those used for solar energy conversion.¹¹⁴ It addresses a central challenge in fabricating high-performing devices by enabling precision processing while preserving essential optoelectronic properties. Unlike conventional hybrid ligand passivation methods that focus mainly on stability and charge transport, the CLIP approach introduced by Himchan Cho and colleagues represented a pioneering expansion of functionality.¹¹⁵ Its core innovation involved the dynamic transformation and controlled removal of photosensitive ligands to achieve high-resolution patterning, constituting an advanced form of ligand interface engineering. As illustrated in Fig. 7(n), ultraviolet light cleaved the ligands bonded to the InP QD surface, modifying their wettability and allowing patterning through differential solubility. A key achievement of this method was its ability to combine fine processing of InP QDs with effective passivation of their optical characteristics. The patterning process preserved 70% of the initial PLQY and maintained optical stability, as shown in Fig. 7(o). Throughout this process, the absorption and PL spectral features of the QDs remained consistent, confirming that the dynamic ligand design sustained surface passivation quality and safeguards fundamental optoelectronic properties. This approach thereby created new possibilities for scalable fabrication of high-performance InP QDs-based optoelectronic devices requiring precise patterning, including components for solar optoelectronic devices.

3.3 Doping and surface treatment

3.3.1 Cationic doping. Cationic doping serves as an effective method for tailoring the electrical and optical characteristics of InP QDs through the incorporation of foreign cations such as transition metal ions (e.g., Cu⁺, Mn²⁺) or isovalent substitutes (e.g., In³⁺).^7,116–118 This strategy allows the atomic-level manipulation of band structure, emission spectra, and charge carrier dynamics with preserved QD structure.^119,120 Additionally, the dopant-induced mid-gap states and modified energy alignment are able to achieve tunable emission extended to near-infrared region and enhanced charge separation, rendering the doped InP QDs highly suitable for applications in bioimaging, photovoltaics, and light-emitting devices.^121,122

For instance, Jiang's group reported the Ga-doped InP QDs synthesized via Ga³⁺-for-In³⁺ cation exchange, which exhibited significantly enhanced PL intensity and a gradual decrease in UV-vis absorption with doping time (Fig. 8(a) and (b)).¹²¹ At 320 °C, the PL peak initially redshifted (609–615 nm, 10 min) due to Ostwald ripening, which was then blue-shifted to 589 nm over 50 min with further cation exchange and core etching (Fig. 8(c)). Concurrently, the PL broadened (FWHM >70 nm after 30 min), yet the PLQY increased and stabilized near 25%, demonstrating the effective optical tuning of InP QDs via Ga³⁺ doping. In another study, Tian et al. also employed cationic doping to modulate the optoelectronic properties of InP-based QDs,³⁶ wherein the gradient In³⁺-doped InP/ZnSe QDs were constructed and the tuning of In³⁺ content established an internal electric field (Fig. 8(d)), which induced a transition from type-I to quasi-type-II band alignment for facilitated separation and transfer of photogenerated carriers. Consequently, as evidenced by the UV-vis absorption and PL spectra (Fig. 8(e) and (f)), both the absorption excitonic peaks and the PL emission peaks exhibited a gradual redshift as a result of the In³⁺ doping that effectively narrowed the overall band gap of the QDs, representing a promising pathway for tailoring their optical behavior through cationic incorporation. Liu et al. also investigated the modulation of band alignments in InP QDs through Cu and Mn doping (Fig. 8(g)).¹²³ It is found that both dopants could reduce the optical band gap of InP QDs, in which the Cu doping led to dual emission originated from both dopant states and band-edge recombination, while the Mn doping facilitated the charge transport by introducing shallow trap states, manifesting the importance of dopant selection in tailoring the charge dynamics of InP-based QDs.

Fig. 8 Cationic doping strategy in InP-based QDs. (a) The schematic illustration for the synthesis of Ga-doped InP cores, (b) UV-vis absorption and (c) the normalized PL spectra of aliquots taken during the Ga³⁺ doping process for InP QDs. (a)–(c) Reproduced with permission.¹²¹ Copyright 2024 Springer Nature. (d) Band structure modulation through gradient In³⁺ doping in ZnSe shells, (e) UV-vis absorption and (f) PL emission spectra with increasing doping concentration. (d)–(f) Reproduced with permission.³⁶ Copyright 2024 American Chemical Society. (g) Band alignments of Cu- and Mn-doped InP QDs derived from experiment analysis. (g) Reproduced with permission.¹²³ Copyright 2024 Elsevier.

3.3.2 Surface treatment. Surface treatment plays a vital role in improving the optical properties of InP QDs by passivating the surface and interfacial defects that degrade charge transport and emission efficiency.^10,124–127 A common approach involves the construction of a surface passivation layer to suppress these defects. For instance, as illustrated in Fig. 9, Baek et al. reported a UV-induced degradation mechanism in InP/ZnSe/ZnS QDs involving the surface oxidation and ZnO domain formation, which facilitate the ZnS etching and In diffusion to induce lattice dislocations (Fig. 9(a)).⁸⁸ This degradation is substantially suppressed under inert atmosphere, with PL lifetime remained stable near 37.7 ns in argon when compared to a decline to 30.1 ns in air (Fig. 9(b)). Consequently, the stabilization of the PL lifetime indicated that the photogenerated carriers could be more effectively utilized for enhancing the ultimate performance of solar energy conversion devices.¹⁰⁶

Fig. 9 Surface treatment strategy for InP QDs. (a) Schematic of UV degradation mechanism involving ZnO formation and In diffusion and (b) comparison of PL lifetime evolution in air versus argon atmosphere for InP/ZnSe/ZnS QDs. (a), (b) Reproduced with permission.⁸⁸ Copyright 2024 Springer Nature. (c) ZnF₂-mediated synthesis of InP QDs with high PLQY and narrowed emission and (d) corresponding monoexponential PL decay profile. (c), (d) Reproduced with permission.¹³⁰ Copyright 2022 American Chemical Society. (e) Various metal fluoride treatments highlighting the optimized InF₃ treatment for enhanced surface passivation, (f) HF-free InF₃ treatment of InP QDs to achieve a high PLQY over 90% and (g) associated PL lifetime extension. (e)–(g) Reproduced with permission.⁷⁰ Copyright 2024 American Chemical Society. (h) In situ HF generation approach for surface reconstruction, (i) temperature-dependent PLQY improvement and (j) PL lifetime evolution with ZnCl₂ co-treatment for InP QDs. (h)–(j) Reproduced with permission.¹³¹ Copyright 2022 American Chemical Society.

The strategic application of fluoride-based treatments alongside sophisticated shell engineering has also emerged as an effective approach for mitigating the nonradiative recombination, which in turn improves both the optical properties and environmental stability.^23,128,129 Li et al. found that the generated HF through the reaction of ZnF₂ and oleic acid under heating could be used to alleviate the surface defects of InP QDs (Fig. 9(c)),¹³⁰ resulting in a PLQY of 90% along with a narrower FWHM (Fig. 9(d)). It is demonstrated that while such fluoride-mediated surface passivation can enhance the PLQY of InP QDs, the involvement of direct HF treatment still poses safety risks and leads to the loss of QD material. Therefore, Arjan J. Houtepen et al. proposed a simple post synthesis HF-free treatment method based on treating the surface of InP QDs with different fluorides (InF₃, ZnF₂, AlF₃ and MgF₂) (Fig. 9(e)).⁷⁰ The results showed that the InF₃-treated InP QDs exhibited the highest PLQY value of 70%. On this basis, the processing temperature of InF₃ was further optimized to reach a PLQY of up to 93% (Fig. 9(f)). Meanwhile, by comparing the PL decay lifetime of InP QDs before and after InF₃ treatment, they found that the PL decay was almost single exponential and the lifetime prolonged considerably after treatment (Fig. 9(g)), suggesting the suppressed non-radiative recombination in QDs. The lifetime extension was originated from the InF₃ treatment that effectively neutralized the non-radiative recombination centers, which is essential for developing high-performance QDs-optoelectronic devices with superior efficiency.⁷⁰ Furthermore, this group proposed an alternative method involving a water-free and safe post-synthetic treatment that generated HF in situ from benzoyl fluoride to substantially enhance the PLQY of InP QDs, as shown in Fig. 9(h).¹³¹ Specifically, the PLQY maintained below 5% at both room temperature and 90 °C regardless of the treatment duration (Fig. 9(i)), while the PLQY exceeded 70% when the temperature reached 200 °C and stabilized within 5 minutes, indicating a non-negligible activation energy barrier for surface reconstruction. Subsequently, the ZnCl₂ was introduced as a cooperative ligand to further enhance the PLQY to 85% and prolong the PL decay lifetime (Fig. 9(j)). Both studies successfully circumvented the safety hazards associated with direct HF usage for effective surface passivation, offering diverse pathways for synthesizing high-quality InP QDs with outstanding optical properties.

4. Photocatalytic and photoelectrochemical applications

Engineering InP QDs via advanced synthetic control, tailored core/shell architectures, strategic doping and sophisticated surface treatment could offer exceptional optoelectronic properties, including high PLQY, broadband light absorption, suppressed charge recombination and optimized charge carrier kinetics, holding great potential in solar-driven energy conversion applications. The precise manipulation of the composition and interface of InP QDs directly dictates their properties as either light-harvesting photosensitizers or active catalysts. It is therefore imperative to explore how these engineered nanomaterials can be translated into functional devices or systems, examples include promising solar energy conversion applications in PC and PEC processes, where the QDs enable the transformative reactions such as hydrogen evolution, CO₂ reduction, ammonia synthesis, and H₂O₂ generation (Table 1), paving the way for future low-cost, eco-friendly and sustainable solar fuel production system.

Table 1 Summary of various typical InP QDs-based solar-driven energy conversion applications

QDs	App	Reaction process	Product evolution rate	Stability	Ref.
w-InP	PC	H2 evolution	0.6 µmol h^−1 cm^−1	1 h	26
InP/InPS/ZnS	PC	H2 evolution	102 µmol mg^−1 h^−1	16 h	132
InP/ZnSeS:Cu/ZnS	PC	H2 evolution	337.5 µmol g^−1 h^−1	8 h	123
InP/ZnSe–G–In	PEC	H2 evolution	—	50 min	36
InP/ZnSeS:Al	PEC	H2 evolution	73.7 µmol cm^−2 h^−1	2 h	133
InP/ZnSe	PEC	H2 evolution	—	1 h	134
InP/ZnSeS-VZn	PEC	H2 evolution	107.1 µmol cm^−2 h^−1	13 h	135
InP/ZnS-Re	PC	CO2 reduction	TON of 52	6 h	136
InP	PC	CO2 reduction	TON of ∼51 000	420 h	32
Bacteria sporomusa ovata/InP	PC	CO2 reduction	0.89 mmol L^−1 h^−1	168 h	137
InP	PC	N2 fixation	430 µmol g^−1	2 h	138
InP/ZnSe	PC	N2 fixation	∼2.7 × 10^7 mol mol^−1 CFUinitia^−1	10 h	139
InP QDs-S^2−	PC	N2 fixation	0.58 µmol cm^−2 h^−1	12 h	140
MCC-InP	PC	H2O2 generation	TON of 173 000	12 h	107
InP/GaP/ZnSe	PEC	H2O2 generation	1.32 µmol min^−1 cm^−2	5 h	16

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4.1 H₂ evolution

Semiconductor QDs, particularly cadmium-free InP-based QDs, have recently advanced the development of efficient solar-driven hydrogen evolution systems due to their tunable bandgaps, broad light absorption, and favorable band alignments for water reduction.^{1,13,15,86,141–143} A variety of strategies such as multispectral absorption engineering, controlled shell growth, elemental doping and interfacial design have been employed to overcome the limitations of InP QDs in charge carrier extraction and device stability.^144–147

As illustrated in Fig. 10(a) and (b), David et al. developed a “rainbow” PC system to efficiently utilize the solar spectrum using size-graded InP QDs.²⁶ In this case, smaller QDs (2.7 nm) absorbed the high-energy photons while larger ones (4.5–6.9 nm) captured the lower-energy photons, thus increasing the absorbed power density by 23 mW cm⁻² (Fig. 10(a)). Based on this design, smaller InP QDs have demonstrated superior hydrogen generation rates and other InP QDs with different sizes yielded a collective generation rate approaching the sum of their individual performance. This synergistic effect led to an enhanced hydrogen production by merging the broad spectral absorption of larger QDs with the high efficiency of smaller ones (Fig. 10(b)). In another work, Gao's group illustrated the important influence of shell thickness in InP-based core/buffer/shell (CBS) QDs (inserting S_x–In–P_1−x buffer monolayer between the core and thin ZnS shell), which resulted in an improved PC hydrogen evolution rate.¹³² Fig. 10(c) demonstrated that ZnS surface engineering enhanced the PC activity of QDs, with CBS-100 QDs achieving a 77-fold improvement over bare InP QDs at the optimal 1.87 monolayer thickness for H₂ evolution. Fig. 10(d) revealed that the CBS-100 QDs exhibited a sevenfold higher PC H₂ production performance than the optimized InP/ZnS QDs without the S_x–In–P_1−x buffer layer. It is revealed that such interfacial structure minimized the lattice mismatch and facilitated the charge separation for efficient exciton tunneling, while the PC activity of QDs declined beyond the optimal thickness, since the thicker shells further impeded exciton transfer to the QDs surface.

Fig. 10 Solar-driven hydrogen evolution using InP-based QDs. (a) Absorption spectra and (b) PC H₂ production rates of size-controlled InP QDs and their hybrid systems. (a), (b) Reproduced with permission.²⁶ Copyright 2024 American Chemical Society. (c) Comparison of H₂ evolution performance between bare InP and core-buffer-shell structured QDs and (d) the influence of sulfur precursors on the PC H₂ generation activity of InP/ZnS QDs. (c), (d) Reproduced with permission.¹³² Copyright 2023 Royal Society of Chemistry. (e) PC H₂ production performance of undoped, Cu-doped, and Mn-doped InP QDs and (f) transient photocurrent spectra. (e), (f) Reproduced with permission.¹²³ Copyright 2024 Elsevier. (g) Schematic of InP core–shell QDs-based PEC cell and (h) corresponding linear sweep voltammetry curves showing photocurrent response. (g), (h) Reproduced with permission.³⁶ Copyright 2024 American Chemical Society. (i) Schematic of the Al-doped InP/ZnSeS-based photoelectrodes for PEC H₂ generation and (j) relevant H₂ evolution rates. (i), (j) Reproduced with permission.¹³³ Copyright 2024 Wiley-VCH. (k) The η_sep curves of different surface-treated InP/ZnSeS QDs-based photoanodes. (k) Reproduced with permission.¹³⁵ Copyright 2025 Wiley-VCH.

The charge carrier dynamics of InP-based QDs in PC H₂ generation could also be effectively tuned through elemental doping. Specifically, Cu⁺ doping enables the introduction of hole-trapping states for suppressed charge recombination, which leads to an efficient cocatalyst-free operation to reach a H₂ yield rate up to 2700 µmol g⁻¹ (Fig. 10(e)).¹²³ In contrast, Mn²⁺ doping predominantly enhanced the charge consumption and this positive impact of optimal doping was further verified by transient photocurrent responses (Fig. 10(f)), wherein the Cu-doped QDs showed a photocurrent of about 80 µA, which is substantially higher than that of the Mn-doped (≈35 µA) and undoped QDs (≈14 µA).

The optimization of dopant concentration and the selection of dopant species represent two important research directions for enhancing the solar-driven H₂ evolution performance of InP-based QDs. For doping concentration control, Tian et al. employed the gradient In³⁺ doping in InP/ZnSe QDs to establish a built-in electric field, thereby facilitating the interfacial charge transfer in the QDs-based PEC device (Fig. 10(g)).³⁶ This approach enabled the identification of an optimal In³⁺ doping level and yielded a maximum saturated photocurrent density of 8.7 mA cm⁻² for PEC H₂ generation (Fig. 10(h)). Similarly, our group also explored the incorporation of aluminum (Al) as a dopant in InP/ZnSeS QDs for PEC H₂ evolution (Fig. 10(i)).¹³³ The underlying mechanism involves the oxidation of Al species during PEC operation to form a passivation layer that suppressed the surface defects and trap states on the QDs. Concurrently, Al occupies zinc lattice sites as shallow donors, which effectively mitigated the non-radiative recombination and enhanced the extraction efficiency of photogenerated electrons from InP/ZnSeS QDs. Owing to this dual functional mechanism, the Al-doped InP/ZnSeS QDs achieved a PEC hydrogen evolution rate of 73.7 µmol cm⁻² h⁻¹ with a faradaic efficiency of 68.9% (Fig. 10(j)).

Following the exploration of elemental doping strategies, further advancements in surface engineering have demonstrated remarkable efficacy in regulating charge carrier dynamics of InP-based QDs for enhanced H₂ evolution. Our group recently developed a two-step surface engineering approach to precisely manipulate the photoinduced charge carrier kinetics in classical InP/ZnSeS QDs,¹³⁵ which was achieved by constructing Zn vacancy (V_Zn)-associated under-coordinated Se/S sites, followed by Cl⁻ ligand exchange. The introduced V_Zn-under-coordinated sites function as effective hole-trapping centers to promote charge separation, while the subsequent Cl⁻ ligands induced a localized internal electric field that further enhanced the carrier extraction. As compared to the maximum charge separation efficiency (η_sep) of 39% obtained for the untreated InP/ZnSeS QDs, the η_sep of the InP/ZnSeS-V_Zn QDs-based photoanode increased to 51% (Fig. 10(k),), underscoring the beneficial role of V_Zn-related sites in improving the charge separation. After Cl⁻ treatment, the η_sep of the InP/ZnSeS-V_Zn-Cl-based PEC device was further elevated to 76%, confirming that the ligand-induced electric field provided an additional driving force for efficient carrier transport. As a result, the optimized QDs delivered a notable photocurrent density in a PEC hydrogen evolution system, highlighting the practical potential of synergistic vacancy and ligand engineering in solar fuel generation.

4.2 CO₂ reduction

PC and PEC reduction of CO₂ into chemical feedstocks using semiconductor QDs offers a promising technique toward carbon-neutral energy cycles.^148–150 Among them, InP-based QDs performed effectively as photosensitizers and maintained broad compatibility with numerous co-catalysts in CO₂ reduction systems.¹⁵¹ For example, Zheng and his colleagues developed a hybrid catalyst system comprising covalently bonded InP/ZnS QDs and Re-complexes (Fig. 11(a)),¹³⁶ in which the Re-QD samples were dispersed in CH₃CN with 10% triethanolamine (TEOA) as a sacrificial donor for PC CO₂ reduction. As shown in Fig. 11(b), the PC performance was strongly dependent on the size of InP/ZnS QDs, with smaller QDs (2.3 nm) enabling a faster multi-electron transfer to achieve a superior CO production with a turnover number (TON) of 52 and 7% overall apparent quantum yield (AQY), distinctly outperforming the larger QD counterparts. Furthermore, Fig. 11(c) exhibits that these QDs facilitated the 8-electron transfer for CH₄ generation, thus delivering a TON of 6 with 0.9% AQY. In parallel, Sang Ook Kang et al. constructed an innovative hybrid photocatalyst by immobilizing InP QDs onto TiO₂ support coordinated with a Re complex (ReP) for PC CO₂ reduction.³² As illustrated in Fig. 11(d), the TiO₂ substrate promoted efficient electron transfer from photoexcited QDs via rapid oxidative quenching for enhanced interfacial charge separation. Under the optimized QD loading of 1.6 mg (Fig. 11(e)), the hybrid catalyst exhibited a CO TON of 2500 within 26 h with an AQY of 3.27%. Remarkably, this QD system showed an outstanding photostability, accumulating a total TON of 51 000 over 420 h without QD degradation. Additionally, as shown in Fig. 11(f), the PC CO₂ reduction performance of this InP QD-TiO₂-ReP hybrid PC system was further enhanced with Brønsted acid additives [(H₂O), 2,2,2-trifluoroethanol (TFE), or TEOA], which is due to the facilitated CO₂-to-CO conversion through proton-coupled electron transfer that resulted in efficient and durable PC CO₂ reduction.

Fig. 11 InP-based QDs for solar-driven CO₂ reduction. (a) The proposed reaction mechanism for size-dependent InP/ZnS QDs coupled with a Re complex and the measured PC (b) CO and (c) CH₄ production rates with corresponding AQYs. (a)–(c) Reproduced with permission.¹³⁶ Copyright 2024 Wiley-VCH. (d) Charge transfer mechanism in the InP QD-TiO₂-ReP hybrid PC system, (e) Influence of photosensitizer concentration on CO generation and (f) CO production rates using different proton donors. (d)–(f) Reproduced with permission.³² Copyright 2022 American Chemical Society. (g) Schematic of the S. ovata/InP QDs biohybrid system for artificial photosynthesis. (h) Total acetate yield and (i) cumulative acetate production over seven days under light and dark conditions. (g)–(i) Reproduced with permission.¹³⁷ Copyright 2022 Elsevier.

In another work, Liu et al. demonstrated that InP/ZnSe/ZnS QDs could be engineered into anaerobic bacteria Sporomusa ovata (S. ovata) as a non-photosynthetic bacterial systems for CO₂ photoreduction, enabling efficient light-driven CO₂-to-acetate conversion (Fig. 11(g)).¹³⁷ Under light illumination, the hybrid system showed largely enhanced acetate production compared to the dark condition and the addition of K₃Fe(CN)₆ as an electron mediator further improved the chemical yield (Fig. 11(h)). The temporal evolution of acetate production (Fig. 11(i)) revealed that the electron mediator accelerated the process by facilitating extracellular electron transfer. This work highlights the unique advantage of intracellular InP-based QDs in directly channeling photogenerated electrons for microbial CO₂ reduction.

4.3 Ammonia synthesis

PC and PEC nitrogen reduction using InP QDs presents a promising pathway for sustainable ammonia synthesis, potentially circumventing the high energy demands of conventional Haber–Bosch processes.^152–154 For example, Pramod and colleagues developed a visible-light-driven system for ammonia synthesis from nitrate and nitrite ions using InP QDs as photocatalysts.¹³⁸ Quaternary ammonium groups with permanent positive charges electrostatically guided NO₃⁻ and NO₂⁻ reactants toward [+] InP QDs, thereby increasing their local concentration near the photocatalyst surface (Fig. 12(a)). This configuration promoted efficient electron transfer from photoexcited QDs to the adsorbed reactants. Comprehensive optimization experiments showed that increasing the concentration of [+] InP QDs progressively enhanced both the NH₄⁺ production and NO₃⁻ conversion efficiency during two hours of visible-light irradiation (Fig. 12(b)).

Fig. 12 InP-based QDs for solar-driven ammonia synthesis and H₂O₂ generation: (a) schematic of electrostatic interaction between surface-modified InP QDs and nitrate ions. (b) Corresponding ammonium production and nitrate conversion efficiency as a function of catalyst loading. (a), (b) Reproduced with permission.¹³⁸ Copyright 2024 American Chemical Society. (c) The proposed electron transfer pathway in the InP QDs-A. vinelandii biohybrid system. (d) Comparison of ammonia production rate under light and dark conditions. (c), (d) Reproduced with permission.¹³⁹ Copyright 2022 American Chemical Society. (e) Schematic of charge transfer mechanism in the sulfurized InP QDs/MIL-100(Fe) heterostructure and (f) NH₃ yield and (g) faradaic efficiency at different applied potentials. (e)–(g) Reproduced with permission.¹⁴⁰ Copyright 2024 Wiley-VCH. (h) Band alignment of MCC-InP QDs with two-electron O₂ reduction and H₂O oxidation potentials. (i) PC H₂O₂ production via 2e⁻ ORR using InP QDs with different ligands and core/shell structures. (h), (i) Reproduced with permission.¹⁰⁷ Copyright 2025 Wiley-VCH. (j) Charge separation and H₂O₂ formation mechanism in ZIS-Se photoanode modified with InP-based QDs. (k) Faradaic efficiency for H₂O₂ generation as a function of applied bias and (l) relationship between theoretical charge consumption and the measured H₂ and H₂O₂. (j)–(l) Reproduced with permission.¹⁶ Copyright 2024 Elsevier.

InP-based QDs have been demonstrated as potential building blocks to be integrated with the nitrogen-fixing bacterium Azotobacter vinelandii for light-driven nitrogen fixation.¹³⁹ It is revealed that culturing the bacteria with InP/ZnSe core–shell QDs during exponential growth enhanced the cellular QDs uptake and substantially improved the ammonia yield when compared to the physically mixed systems. As depicted in Fig. 12(c), the InP/ZnSe QDs absorbed into the interior of bacterial cells could directly transfer the photoexcited electrons to the MoFe protein component of nitrogenase and initialized the nitrogen reduction into NH₃. The photogenerated holes are efficiently scavenged by cytoplasmic glutathione (GSH) and regenerated via GSH reductase, maintaining charge balance throughout the PC cycle. Under standardized experimental conditions with equivalent QDs loading per cell, the QDs-bacteria hybrid demonstrated superior ammonia production over control groups under LED irradiation, as quantitatively shown in Fig. 12(d). This biohybrid system exemplifies an efficient strategy for solar-powered nitrogen fixation by directly coupling semiconductor nanomaterials with microbial metabolic pathways.

PEC ammonia synthesis is another promising nitrogen fixation route, yet its practical efficiency is limited by the six-electron nitrogen reduction process.^155,156 Considering this limitation, Zhou and colleagues designed a hybrid catalyst by integrating sulfur ligand-modified InP QDs with MIL-100(Fe) to enhance the PEC nitrogen fixation performance (Fig. 12(e)),¹⁴⁰ showing that the hybrid composite prepared with 5 mL of InP QDs solution could deliver the highest activity. Fig. 12(f) compared the ammonia production rates of MIL-100(Fe) and the hybrid catalyst under various applied biases, presenting significant performance improvement upon InP QDs incorporation. Specifically, at −0.2 V versus RHE, the hybrid catalyst achieved a maximum ammonia yield of 0.58 µmol cm⁻² h⁻¹, representing a 3.09-fold enhancement over the pristine MIL-100(Fe) (Fig. 12(g)). Consistently, the highest faradaic efficiency was also achieved at this potential for both catalysts, while more negative potentials were inclined to induce the competing hydrogen evolution reaction. Control experiments further demonstrated the essential role of Fe–S bonds in promoting the interfacial electron transfer, with no detectable hydrazine byproducts that confirmed the high selectivity toward ammonia formation. These findings recognized InP QDs as effective photocatalysts or photoelectrocatalysts for nitrogen fixation via nitrate and nitrite reduction pathways.

4.4 H₂O₂ generation

Apart from nitrogen fixation, InP QDs can also be utilized for sustainable H₂O₂ production via PC and PEC routes,^157–160 since the high selectivity in the two-electron pathway could be achieved by strategically modifying their surface properties and heterostructures to suppress competing reactions.¹⁵⁸ Jaehwan et al. demonstrated that InP/ZnSe/ZnS QDs modified with thiostannate (Sn₂S₆⁴⁻) molecular metal chalcogenide (MCC) complexes were prone to drive the two-electron oxygen reduction reaction (ORR) over water oxidation reaction (WOR) under illumination,¹⁰⁷ thereby resulting in a substantial enhancement of H₂O₂ production, as schematically shown in Fig. 12(h). Quantitative analysis in Fig. 12(i) exhibited that the MCC-InP QDs produced 278.5 µM of H₂O₂ which represented a 2.84-fold increment compared to that of the MPA-InP QDs (98.0 µM). Control experiments under nitrogen atmosphere or dark conditions showed negligible H₂O₂ formation, confirming that the detected H₂O₂ was originated specifically from the PC ORR pathway and highlighting the MCC-InP QDs complexes as effective surface modifiers for promoting selective PC H₂O₂ generation.

For PEC H₂O₂ generation system, our group designed a photoanode composed of InP/GaP/ZnSe QDs decorated on selenium-doped ZnIn₂S₄ (ZIS-Se) to enhance the H₂O₂ generation efficiency.¹⁶ The heterojunction formed between the InP-based QDs and ZIS-Se induced favorable band bending that promoted the two-electron WOR pathway toward H₂O₂ instead of the competing four-electron oxygen evolution (Fig. 12(j)). Faraday efficiency (FE) measurements further confirmed this behavior across a potential range of 0.65 to 1.85 V versus RHE (Fig. 12(k)), in which the ZIS-Se/QDs photoanode achieved a remarkable average H₂O₂ Faraday efficiency of 86% between 0.85 and 1.85 V, outperforming both the ZIS-Se and pristine ZIS electrodes. At higher applied biases, the Faraday efficiency decreased moderately to 80.6%, which is attributed to the increasing contribution of alternative water oxidation pathways such as oxygen evolution. As illustrated in Fig. 12(l), the simultaneous production of H₂O₂ at the photoanode and hydrogen at the cathode was quantified, showing close agreement between experimental yields and theoretical electron counts. The PEC H₂O₂ generation rate of as-fabricated ZIS-Se/QDs photoanode reached up to 1.32 µmol min⁻¹ cm⁻², which is competitive among various other state-of-the-art PEC H₂O₂ production systems.

5. Challenges and perspectives

This review has systematically summarized the recent advances of InP QDs in the field of solar energy conversion. Through optimized synthetic methods including hot-injection and heat-up approaches, high-quality QDs with narrow size distribution and PLQYs exceeding 90% have been achieved.¹⁸ Interface engineering of sophisticated core/shell architectures (e.g., InP/ZnSeS/ZnS) and hybrid ligand strategies have effectively suppressed defect states and significantly enhanced charge separation efficiency. These material breakthroughs have enabled exceptional performance of InP QDs in PC and PEC systems, particularly demonstrating unique advantages in direct solar-to-chemical energy conversion pathways.

Comparative analysis with established QD systems further highlights the competitive advantages of InP QDs. As compared to conventional toxic CdSe QDs, their heavy-metal-free nature complies with RoHS environmental regulations and the larger exciton Bohr radius of InP provides broader tunability of optical properties.¹⁶¹ In terms of prevailing perovskite QDs, InP-based QDs have demonstrated significantly superior environmental stability due to their robust inorganic shell structures. For example, InP/ZnSe/ZnS QDs have maintained stable operation for two years in outdoor luminescent solar concentrators (LSC) whereas perovskite QDs rapidly degrade under similar conditions.¹⁶²

Beyond these comparisons with other QD systems, InP QDs also present distinct advantages over conventional bulk photovoltaic technologies. Although silicon-based photovoltaics have achieved high efficiency and low cost in standard solar panels, InP QDs offer unique benefits in specialized applications.¹⁶³ Their solution processability enables low-temperature fabrication on flexible substrates, making them suitable for building-integrated photovoltaics (BIPVs) where traditional rigid silicon panels are impractical.^56,60,89,164 Beyond these advantages, InP QDs enable direct solar-to-chemical conversion pathways that bypass the multi-stage energy losses inherent in conventional photovoltaic–electrolysis systems. For instance, in PC CO₂ reduction, InP QDs have achieved a TON exceeding 51 000 with stable operation maintained for 420 hours, demonstrating a new route toward higher system-level energy utilization efficiency.³² These characteristics, which combine solution processability for flexible devices, tunable bandgaps for spectral optimization and robust stability for long-term operation, establish clear conditions where InP QDs can complement or compete with conventional photovoltaic routes, particularly in applications requiring durability and direct chemical production.

Nevertheless, the large-scale application of InP QDs faces critical challenges. Global indium production is limited to 800–900 tons per year with over 70% consumed by the indium tin oxide (ITO) industry, leading to supply constraints and price fluctuations between $150–400 per kilogram.^165,166 This resource bottleneck necessitates both the development of more efficient synthesis methods to reduce indium consumption and the establishment of comprehensive recycling systems.^56,167 Through continued innovation in these directions, InP QDs are expected to play a unique role in specific solar energy conversion fields. Beyond these fundamental constraints, additional core challenges require resolution:

5.1 Developing sustainable and scalable synthetic methodologies

A primary impediment to the widespread adoption of InP QDs is the reliance on highly toxic, expensive, and air-sensitive phosphorus precursors (e.g., P(TMS)₃), alongside energy-intensive batch-processed synthesis that hinder reproducibility and scale-up.^168,169 The inherent limitations of organic solvents, which decompose below 400 °C, further restrict the preparation of QDs with high crystallinity and low defect densities.^53,56,170

Future research should prioritize the development of safer precursor chemistries, such as aminophosphines and phosphine–carbon monoxide adducts, which offer improved handling and tunable reactivity. A transformative pathway lies in adopting non-coordinating solvent systems or molten salt matrices (e.g., LiCl/KCl) for high-temperature (>400 °C) synthesis (as demonstrated for GaAs and InAs QDs),¹⁷¹ which facilitates atomic rearrangement and defect annihilation to realize superior optoelectronic properties.^172,173 Coupling these advanced reactors with machine learning-guided optimization of kinetic parameters (heating rates, precursor stoichiometry) and in situ optical spectroscopy are also crucial for synthesizing InP QDs with precise control over size distribution, composition, and ultimately, batch-to-batch uniformity at commercially relevant scales.

5.2 Achieving robust surface passivation and interface control

The optoelectronic properties and stability of InP QDs-based devices are severely compromised by surface defects as trap states for charge carriers and the dynamic nature of surface ligands that leads to desorption and oxidation under operational conditions.^8,86 Current ligand exchange strategies often improve charge transport at the expense of increased vulnerability to photocorrosion, and a fundamental understanding of the binding configurations and passivation mechanism remains lacking.

Further investigations of InP QDs-based devices require a multi-faceted approach combining advanced spectroscopy, simulation, and new passivation paradigms. Operando X-ray photoelectron spectroscopy (XPS) and surface-enhanced Raman spectroscopy (SERS) can probe the chemical evolution of the QDs surface during solar-driven PC or PEC processes.^174,175 Besides, the cryo-electron microscopy (cryo-EM) could be employed to resolve the atomic structure of the QD-ligand interface and core/shell heterostructures with minimal beam damage, providing direct visualization of surface reconstruction and defect sites that govern charge trapping and passivation efficiency.^176,177 Density functional theory (DFT) calculations are essential to map the trap state distributions and identify the optimal ligand binding configurations.^178,179 Beyond small molecules, future work may explore the atomic-layer deposition (ALD) of ultrathin, conformal oxide layers (e.g., TiO₂, Al₂O₃) and the use of cross-linkable ligands to create a robust, inorganic–organic hybrid shell that simultaneously passivates traps, enhances stability, and facilitates charge extraction to reactants or electrodes.^180,181

5.3 Engineering advanced heterostructures for charge carrier manipulation

While bare InP QDs exhibit efficient light absorption, their utility in PC and PEC processes is limited by rapid charge recombination and a lack of directed charge flow to the catalytic sites.^32,86 Simple hybrid systems, such as QDs-molecular catalyst assemblies, often suffer from inefficient interfacial electron transfer and instability.¹⁸²

The strategic construction of type-II heterostructures (e.g., InP/ZnTe, InP/CdS) or gradient alloyed shells (e.g., InP/ZnSeS) is a powerful tool for spatially separating electrons and holes to prolong carrier lifetime.^183–185 Moreover, integrating earth-abundant molecular cocatalysts (e.g., Ni-based complexes for proton reduction, Co-based macrocycles for CO₂ reduction) requires precise control over the QDs–cocatalyst interface,^186,187 while tuning the anchor group and the molecular structure of the catalyst can optimize the electronic coupling and proton relay pathways. To guide this rational design, future studies could employ transient absorption spectroscopy (TAS) and TRPL to quantify charge transfer rates and efficiencies, directly linking the interfacial structure to function relationship.¹³⁴ To gain a more comprehensive picture of charge dynamics, future studies may utilize TAS together with operando X-ray absorption spectroscopy (XAS) to probe the oxidation state and local coordination environment of QDs’ active centers during the actual PC or PEC reactions, thus directly correlating the electronic structure of QDs with reaction activity and stability.^174,188

5.4 Enhancing stability in operational environments

A critical barrier to practical application is the rapid degradation of InP QDs under continuous illumination in reactive environments, primarily due to photocorrosion initiated by hole accumulation on the surface and oxidation by photogenerated reactive oxygen species.¹⁸⁹

Substantial improvements in operational lifetime demand innovative encapsulation strategies, such as embedding QDs within a protective matrix (e.g., a metal–organic framework, a conductive polymer or a mesoporous oxide) to physically isolate them from the electrolyte while permitting mass transport of reactants.^190–192 Additionally, the design of multi-component sacrificial reagent systems or integrated redox mediators that can efficiently scavenge the holes is a promising yet underexplored avenue.¹⁹³ Establishing standardized protocols for accelerated aging tests of InP QDs under realistic sunlight intensities (e.g., AM 1.5G) and operating conditions will be vital for fairly comparing QD material systems and guiding development toward commercially viable durability.

5.5 Advancing system integration for selective reactions

Current InP QD systems still lack reaction specificity, particularly in complex multi-electron transfer processes.¹⁹⁴ The competition between different reaction pathways, such as the two-electron versus four-electron WOR, is limiting the efficiency and selectivity for valuable chemical production.^195,196

Future work should focus on designing integrated systems with tailored band structures that favor specific reaction pathways. As demonstrated in InP-based QD heterostructure system, the rational interface engineering can effectively steer reaction selectivity toward desired products like hydrogen peroxide.¹⁶ System-level optimization, including matched electrode design and efficient product separation, is also essential for achieving high solar-to-chemical conversion efficiency and economic viability.

Conflicts of interest

There are no conflicts to declare.

Data availability

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

Acknowledgements

X. T. acknowledges the support from National Natural Science Foundation of China (no. W2433035) and Yunnan Key Laboratory of Electromagnetic Materials and Devices, Yunnan University (no. ZZ2024001). X. T. and X. L. acknowledge the support from Solar Energy Integration Technology Popularization and Application Key Laboratory of Sichuan Province (no. 25TYNJS-Z-01, 25TYNJS-Z-04). H. Y. Z. acknowledges the support from National Natural Science Foundation of China (no. 52402138), Sichuan Provincial Innovation and Entrepreneurship Competition (no. S202510639008) and Scientific Research Start-up Project of Mianyang Normal University (no. QD2025A005).

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