The mixed caesium and formamidinium lead triiodide perovskite system (Cs1-xFAxPbI3) in the form of quantum dots (QDs) offers a new pathway towards stable perovskite-based photovoltaics and optoelectronics. However, it remains challenging to synthesize such multinary QDs with desirable properties for high-performance QD solar cells (QDSCs). Here we report an effective ligand-assisted cation exchange strategy that enables controllable synthesis of Cs1-xFAxPbI3 QDs across the whole composition range (x: 0-1), which is inaccessible in large-grain polycrystalline thin films. The surface ligands play a key role in driving the cross-exchange of cations for the rapid formation of Cs1-xFAxPbI3 QDs with suppressed defect density. The hero Cs0.5FA0.5PbI3 QDSC achieves a certified record power conversion efficiency (PCE) of 16.6% with negligible hysteresis. We further demonstrate that QD devices exhibit substantially enhanced photostability compared to their thin film counterparts because of the suppressed phase segregation, retaining 94% of the original PCE under continuous 1-sun illumination for 600 hours.

Metal halide perovskites have been brought to the forefront of research focus in solution-processable photovoltaics, with the device efficiency swiftly surging to over 22% over the past few years. The state-of-the-art metal halide perovskites that have been intensively investigated include toxic lead, which potentially hampers their commercialization process. To address this toxicity issue, intensive recent research effort has been devoted to developing low-toxic metal halide perovskites and their derivatives for photovoltaic applications. Herein, the recent research progress achieved so far in

The presence of surface ligands not only plays a key role in keeping the colloidal integrity and non‐defective surface of metal halide perovskite quantum dots (PQDs), but also serves as a knob to tune their optoelectronic properties for a variety of exciting applications including solar cells and light‐emitting diodes. However, these indispensable surface ligands may also deteriorate the stability and key properties of PQDs due to their highly dynamic binding and insulating nature. To address these issues, a number of innovative surface chemistry engineering approaches have been developed in the past few years. Based on an in‐depth fundamental understanding of the surface atomistic structure and surface defect formation mechanism in the tiny nanoparticles, a critical overview focusing on the surface chemistry engineering of PQDs including advanced colloidal synthesis, in‐situ surface passivation, and solution‐phase/solid‐state ligand exchange is presented, after which their unprecedented achievements in photovoltaics and other optoelectronics are presented. The practical hurdles and future directions are critically discussed to inspire more rational design of PQD surface chemistry toward practical applications.

Solar hydrogen conversion represents a clean and economic approach in addressing global energy and environmental issues, for which efficient photocatalysts have been heavily pursued. Lead halide perovskites are promising candidates for efficient phtocatalysts in solar hydrogen generation due to their attractive properties in light absorption, photo-generated charge transportation and utilization.However, photocatalytic applications of lead halide perovskites have been limited owing to their poor stability in the presence of water or other polar solvent environment. This work presents the rational control of surface ligands in achieving a good balance between stability and photocatalytic activity of CsPbBr 3 quantum dots (QDs). Detailed studies reveal that the deliberate surface ligands engineering is crucial for maximizing photocatalytic activity of CsPbBr 3 QDs while maintain good QD stability. A certain amount of surface ligands protect the CsPbBr 3 QDs from decomposition in moisture during the photocatalytic reaction while still enable efficient charge transfer for photocatalytic reactions on the surface of QDs. The well-controlled CsPbBr 3 photocatalyst shows efficient visible light-driven H 2 generation with outstanding stability (≥ 160h).

Lead halide perovskites have witnessed significant progress in low-cost and high-efficiency photovoltaics, with a rapid increase in photovoltaic efficiencies from 3.8% to a certified record of 25.2% in the past decade. [1-4] However, the viability and practical scale-up implementation are limited by the stability and toxicity of the lead halide perovskites. [5,6] To circumvent these two

Organic–inorganic metal halide perovskites with three‐dimensional (3D) crystal structures have attracted tremendous attention due to their successful demonstrations in varying optoelectronic applications, particularly in photovoltaics (PV). Despite the rapid progress in achieving high performance in optoelectronic devices, the long‐term instability and lead toxicity in 3D perovskites are still two major challenges hindering their steps toward commercialization. To overcome these issues, a series of low‐dimensional perovskites and their derivatives are investigated, aiming at prolonging device lifetime and reducing toxicity. Herein, recent advances of low‐dimensional perovskites and their derivatives in PV with a focus on enhanced long‐term stability and reduced toxicity are reviewed. The fundamental understanding on their crystal structures and properties is presented. Beyond PV, the exploration of low‐dimensional perovskites for other promising optoelectronic applications is also summarized. In addition, the current challenges and future opportunities are discussed to provide a roadmap to the development of low‐dimensional perovskites.

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