Bismuth Incorporation Stabilized α-CsPbI 3 for Fully Inorganic Perovskite Solar Cells

All-inorganic CsPbI 3 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-CsPbI 3 is not stable at room temperature and degrades rapidly to a nonperovskite yellow phase δ-CsPbI 3 . Herein, we introduce a compositional engineering approach via incorporating Bi 3+ in CsPbI 3 to stabilize the α-phase at room temperature. Fully inorganic solar cells based on the Bi-incorporated α-CsPb 1– x Bi x I 3 compounds demonstrate a high PCE of 13.21% at an optimal condition (incorporation of 4 mol % Bi 3+ ) 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-CsPbI 3, which paves the way for further developments of such perovskites and other optoelectronic devices.