Pinhole Healing of Pristine FAPbI₃ Films via Homogeneous Recrystallization with Mixed Vapor of Tetramethylene Sulfoxide and Anisole

Abstract The preparation of pristine formamidinium lead tri‐iodide (FAPbI₃) perovskite films for solar cells applications can be very challenging without methylammonium containing additives. The pinhole‐rich films prepared by methylammonium‐free approach limit the performance of the pristine FAPbI₃ perovskite solar cells (PSCs). This work proposes a recrystallization method employing mixed solvent annealing (MSA) to heal the pinholes in pristine FAPbI₃ perovskite films. The tetramethylene sulfoxide vapor is demonstrated most effective in grains‐merging and pinhole healing, while the addition of a secondary solvent vapor of anisole significantly improved the uniformity of TMSO vapor distribution. The pristine FAPbI₃ PSCs prepared with MSA recrystallized film achieved power conversion efficiencies up to 22.43% and 16.54% on small cells (0.105 cm²) and mini‐modules (12.6 cm²), respectively, showing great potential in upscaling fabrication of perovskite photovoltaics with pristine FAPbI₃.