Anion-exchange assisted sequential deposition for stable and efficient FAPbI3-based perovskite solar cells

PbI2 as precursor has been extensively employed for the fabrication of organic–inorganic hybrid perovskite films for high-efficiency perovskite solar cells (PSCs) by using two-step solution deposition method. However, the resultant perovskite film suffers from the incomplete reaction of PbI2 and the volumetric expansion of the film, affecting both the performance and stability of the PSCs. Here, a single-crystal complex FA4Pb3I6Ac4 (Ac−: CH3COO−) is synthesized, and utilized to replace PbI2 for the fabrication of FAPbI3-based perovskite film in ambient conditions. The solution-processed crystal complex has good film-forming ability, and can be directly converted into stable black-phase FAPbI3 perovskite at room temperature through anion exchange reaction between Ac− and I− upon coating with iodide salt solution. By the strategy, a dense and uniform perovskite film is obtained with reduced trap-state density and prolonged charge lifetime. The champion device delivers a power conversion efficiency (PCE) of 23.65% with high reproductivity. Importantly, the unencapsulated device exhibits a dramatically improved operational stability under temperature and humidity conditions.