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.