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 CsPbI 2 Br perovskites. Herein, a fluorinated organic ammonium halide salt, 4‐trifluoromethyl phenethylammonium iodide (CFPEAI), is incorporated into the surface of CsPbI 2 Br perovskite for the first time. After the CFPEAI modification, the defects of CsPbI 2 Br 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%, a J SC of 15.05 mA cm −2 , and a V OC of 1.20 V. With CFPEAI passivation, the CsPbI 2 Br perovskite film exhibits enhanced hydrophobicity, thereby leading to improved stability for the corresponding PVSC in comparison with the control PVSC without any surface modification.