Efficient and Stable Wide-Bandgap Perovskite Solar Cells Derived from a Thermodynamic Phase-Pure Intermediate

Wide-bandgap perovskites based on alloying cesium and formamidinium lead mixed halides (Cs(x)FA(1-x)Pb(IyBr1-y)(3)) have received great attention due to their potential application in high-efficiency tandem solar cells. However, the fast crystallization of Cs(x)FA(1-x)Pb(IyBr1-y)(3) perovskite films results in a high trap density and hinders the further enhancement of the photovoltaic performance. Herein, an intermediate engineering is developed to retard the fast crystallization of Cs(0.17)FA(0.83)PbI(1.8)Br(1.2) wide-bandgap perovskite by adding FACl in the precursor solution. The introduction of the FACl additive leads to the formation of a thermodynamic phase-pure intermediate which facilitates the further crystallization of a high-quality perovskite thin film at elevated temperature and thus enhances the ultimate device performance. The champion device achieves an efficiency over 19% and exhibits 83.8% retention after 50 days aging without encapsulation.