Surface Passivation of All-Inorganic CsPbI2Br with a Fluorinated Organic Ammonium Salt for Perovskite Solar Cells with Efficiencies over 16%

Surface modification is demonstrated as an efficient strategy to enhance the efficiency and stability of perovskite solar cells (PVSCs). Fluorinated organic ammonium salts featuring a strong hydrophobic nature are seldom used as passivation agents for the surface modification of CsPbI2Br perovskites. Herein, a fluorinated organic ammonium halide salt, 4-trifluoromethyl phenethylammonium iodide (CFPEAI), is incorporated into the surface of CsPbI2Br perovskite for the first time. After the CFPEAI modification, the defects of CsPbI2Br perovskite are significantly passivated with reduced trap densities. The best-performance PVSC with CFPEAI modification shows an excellent power conversion efficiency (PCE) of 16.07% with a high fill factor (FF) of 84.65%, a short-circuit current density (J(SC)) of 15.45 mA cm(-2), and an open-circuit voltage (V-OC) of 1.23 V. In contrast, the control PVSCs without the surface modification exhibit a lower PCE of 14.50% with a FF of 80.56%, aJ(SC)of 15.05 mA cm(-2), and aV(OC)of 1.20 V. With CFPEAI passivation, the CsPbI2Br perovskite film exhibits enhanced hydrophobicity, thereby leading to improved stability for the corresponding PVSC in comparison with the control PVSC without any surface modification.