Near‐Stoichiometric and Homogenized Perovskite Films for Solar Cells with Minimized Performance Variation

Abstract Mixed‐cation, small band‐gap perovskites via rationally alloying formamidinium (FA) and methylammonium (MA) together have been widely employed for blade‐coated perovskite solar cells with satisfied efficiencies. One of the stringent challenges lies in difficult control of the nucleation and crystallization kinetics of the perovskites with mixed ingredients. Herein, a pre‐seeding strategy by mixing FAPbI 3 solution with pre‐synthesized MAPbI 3 microcrystals has been developed to smartly decouple the nucleation and crystallization process. As a result, the time window of initialized crystallization has been greatly extended by 3 folds (i.e. from 5 s to 20 s), which enables the formation of uniform and homogeneous alloyed‐FAMA perovskite films with designated stoichiometric ratios. The resultant blade‐coated solar cells achieved a champion efficiency of 24.31 % accompanied by outstanding reproducibility with more than 87 % of the devices showing efficiencies higher than 23 %.