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 alpha-CsPbl(3) is not stable at room temperature and degrades rapidly to a nonperovskite yellow phase delta-CsPbl(3). Herein, we introduce a compositional engineering approach via incorporating Bi3+ in CsPbl(3) to stabilize the alpha-phase at room temperature. Fully inorganic solar cells based on the Bi-incorporated alpha-CsP1-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 alpha-CsPbl(3), which paves the way for further developments of such perovskites and other optoelectronic devices.