Formamidinium post‐dripping on methylammonium lead iodide to achieve stable and efficient perovskite solar cells

Formamidinium iodide (FAI) based perovskite solar cells (PSCs) have now been established as effective PSCs than methylammonium lead iodide perovskite for several years due to their optimal bandgap and high thermal stability. However, the FAI-based PSCs have humidity issues, due to which mixed cation perovskites are getting popular. MAI-based PSCs have better stability against high humidity but low thermal stabilities. Herein, we prepared highly crystallized, efficient, and large-grain size perovskite films via FAI post-dripping process. In addition, the most promising structures FAI mixed MAPbI3 were explored as stable and effective active layers. The post-dripping of FAI solution just after the MAPbI3 deposition provides a robust long-distance diffusion, long carrier life, and enhanced grain sizes when compared to MAPbI3 PSCs. Based on the facile way of mixed cation perovskite preparation by post-dripping, the power conversion efficiency (PCE) has risen from 15.24% to 17.52% in comparison with the pristine devices. This results in the best quality and large grain perovskite films which enhanced the PSCs' performance by reducing defect density and regulating the crystallization rate.