Lead‐Free All‐Inorganic Cesium Bismuth Iodide‐Based Perovskite Solar Cells: Recent Advances, Current Limitations, and Future Prospects

Remarkable achievements have been made in the development of perovskite solar cells (PSCs) with a rapidly boosting rate of power conversion efficiencies (PCEs) from 3.8% to 26.1%. Nevertheless, the toxicity of lead (Pb) elements and the hygroscopicity of organic cations in high‐efficiency PSCs severely hamper the commercialization of this technology. Consequently, Pb‐free all‐inorganic PSCs have received increasing attention recently to resolve the above‐mentioned toxicity and instability problems. Among various Pb‐free all‐inorganic halide perovskites, cesium bismuth iodide (CBI)‐based perovskites have gained particular attention as light absorbers in PSCs due to the tunable/small bandgaps, long carrier diffusion length/lifetime, and superb sunlight absorption coefficients. Nevertheless, the PCEs of CBI‐based PSCs are still far away from Pb‐based organic–inorganic counterparts because of the low structural dimensions and inferior perovskite film quality. Herein, the recent advances of CBI‐based perovskites as light‐absorbing materials in Pb‐free all‐inorganic PSCs are reviewed by emphasizing the distinct structural/optical/electronic properties and currently existing limitations. Additionally, several distinct strategies to boost the PCEs and robusticity of CBI‐based PSCs are presented. Finally, the unsolved key problems and future directions of CBI‐based PSCs are proposed, aiming to provide important insights for the further development of CBI‐based PSCs to realize sustainable, nontoxic, high‐performance perovskite photovoltaics.