Europium and Acetate Co‐doping Strategy for Developing Stable and Efficient CsPbI2Br Perovskite Solar Cells

All‐inorganic perovskite solar cells have developed rapidly in the last two years due to their excellent thermal and light stability. However, low efficiency and moisture instability limit their future commercial application. The mixed‐halide inorganic CsPbI₂Br perovskite with a suitable bandgap offers a good balance between phase stability and light harvesting. However, high defect density and low carrier lifetime in CsPbI₂Br perovskites limit the open‐circuit voltage (V_oc < 1.2 V), short‐circuit current density (J_sc < 15 mA cm^?2), and fill factor (FF < 75%) of CsPbI₂Br perovskite solar cells, resulting in an efficiency below 14%. For the first time, a CsPbI₂Br perovskite is doped by Eu(Ac)₃ to obtain a high‐quality inorganic perovskite film with a low defect density and long carrier lifetime. A high efficiency of 15.25% (average efficiency of 14.88%), a respectable V_oc of 1.25 V, a reasonable J_sc of 15.44 mA cm^?2, and a high FF of 79.00% are realized for CsPbI₂Br solar cells. Moreover, the CsPbI₂Br solar cells with Eu(Ac)₃ doping demonstrate excellent air stability and maintain more than 80% of their initial power conversion efficiency (PCE) values after aging in air (relative humidity: 35–40%) for 30 days.