Ge Incorporation to Stabilize Efficient Inorganic CsPbI₃ Perovskite Solar Cells

Abstract Aiming at stable CsPbI 3 perovskite solar cells, Ge incorporated for the first time into DMAPbI 3 ‐based precursor systems. Ge incorporation is found to be able to modify crystallization growth of CsPb 1− x Ge x I 3 films and reduce annealing temperature and treatment time by lowering CsPbI 3 formation energy. The champion power conversion efficiency (PCE) of 19.52% is achieved with a certified PCE of 18.8%, which is the highest performance of CsPbI 3 PSCs with alien element‐doping. In addition, in situ formation of GeO 2 can passivate the grain boundary and surface defects, thus significantly improving the moisture resistance of the perovskite film and related devices. Excellent operational stability is achieved with no PCE degradation over 3000 h at a fixed bias voltage of 0.85 V under continuous white LED (6500 K) illumination and a nitrogen atmosphere. This work demonstrates that Ge‐incorporation is a promising way to stabilize CsPbI 3 perovskite solar cells by simultaneously improving perovskite crystallinity and passivating the grain boundary and interfacial defects.