Crystal Growth Regulation of alpha-FAPbI(3) Perovskite Films for High-Efficiency Solar Cells with Long-Term Stability

The two-step sequentially deposition strategy has been widely used to produce high-performance FAPbI(3)-based solar cells. However, due to the rapid reaction between PbI2 and FAI, a dense perovskite film forms on top of the PbI2 layer immediately and blocks the FAI diffusion into the bottom of the PbI2 film for a complete reaction, which results in a low-efficiency and limited reproducibility of perovskite solar cells (PSCs). Here, high-quality alpha-FAPbI(3) perovskite films by crystal growth regulation with 4-fluorobenzamide additives is fabricated. The additives can interact with FAI to suppress the fast reaction between the FAI and PbI2 and effectively passivate the under-coordinated Pb2+ or I- defects. As a result, alpha-FAPbI(3) perovskite films with low trap density and large grain size are prepared. The modified PSCs present a high-power conversion efficiency of 24.08%, maintaining 90% of their initial efficiency after 1400 h in high humidity. This study provides an efficient strategy of synergistic crystallization and passivation to form high-quality alpha-FAPbI(3) films for high-performance PSCs.