Crystal growth regulation of α-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 PbI${}_2$ and FAI, a dense perovskite film forms on top of the PbI${}_2$ layer immediately and blocks the FAI diffusion into the bottom of the PbI${}_2$ film for a complete reaction, which results in a low-efficiency and limited reproducibility of perovskite solar cells (PSCs). Here, high-quality α-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 PbI${}_2$ and effectively passivate the under-coordinated Pb${}^{2+}$ or I${}^{-}$ defects. As a result, α-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 α-FAPbI${}_3$ films for high-performance PSCs. (© 2023 Wiley‐VCH GmbH)