Europium and Acetate Co-doping Strategy for Developing Stable and Efficient CsPbI Br 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 CsPbI Br perovskite with a suitable bandgap offers a good balance between phase stability and light harvesting. However, high defect density and low carrier lifetime in CsPbI Br perovskites limit the open-circuit voltage (V < 1.2 V), short-circuit current density (J < 15 mA cm ), and fill factor (FF < 75%) of CsPbI Br perovskite solar cells, resulting in an efficiency below 14%. For the first time, a CsPbI Br perovskite is doped by Eu(Ac) 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 of 1.25 V, a reasonable J of 15.44 mA cm , and a high FF of 79.00% are realized for CsPbI Br solar cells. Moreover, the CsPbI Br solar cells with Eu(Ac) 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.