Bismuth Incorporation Stabilized α-CsPbI₃ for Fully Inorganic Perovskite Solar Cells

All-inorganic CsPbI3 perovskite is emerging to be an alternative light-harvesting material in solar cells owing to the enhanced stability and comparable photovoltaic performance compared to organic–inorganic hybrid perovskites. However, the desirable black phase α-CsPbI3 is not stable at room temperature and degrades rapidly to a nonperovskite yellow phase δ-CsPbI3. Herein, we introduce a compositional engineering approach via incorporating Bi3+ in CsPbI3 to stabilize the α-phase at room temperature. Fully inorganic solar cells based on the Bi-incorporated α-CsPb1–xBixI3 compounds demonstrate a high PCE of 13.21% at an optimal condition (incorporation of 4 mol % Bi3+) and maintain 68% of the initial PCE for 168 h under ambient conditions without encapsulation. This is the first attempt of partial substitution of the "B"-site of the perovskite to stabilize the α-CsPbI3, which paves the way for further developments of such perovskites and other optoelectronic devices.