Grain size enlargement and controlled crystal growth by formamidinium chloride additive-added degrees ?-CsPbI2Br thin films for stable inorganic perovskite solar cells

Replacing the organic cation with inorganic cation in cesium-based perovskite has fascinated more consideration in halide perovskite solar cells (PSCs) because of their inherent stability and power conversion efficiency (PCE). In the present study, we proposed a new method to increase the stability and PCE of γ-CsPbI2Br-based inorganic perovskite solar cells by adding the formamidinium chloride (FACl) additive into the γ-CsPbI2Br perovskite precursor solution. The FACl additive shows a significant role in the γ-CsPbI2Br perovskite phase to modify the morphology and particular crystal growth to make high-quality perovskite thin films. Also, the FACl additive retards crystallization kinetics to yield a highly crystalline γ-CsPbI2Br perovskite phase, comprising enlarged grain size with reduced charge recombination. The optimum amount of FACl (3 mg/ml) additive-added γ-CsPbI2Br-based device demonstrated a PCE of 15.03%, which is higher than that of the bare γ-CsPbI2Br-based device (12.97%). The stability analysis of the FACl additive-based devices showed high thermal stability that maintains 86% of its initial PCE at 250 h in ambient conditions at 85 °C thermal stress.