CsPbBr3 seeds improve crystallization and energy level alignment for highly efficient CsPbI3 perovskite solar cells

CsPbI3 perovskite solar cells (PSCs) are becoming desirable for their outstanding performance and thermal stability, while their inferior tolerance to moisture restricts further advances. Herein, CsPbBr3 pieces are introduced onto TiO2 electron transport layer (ETL) before CsPbI3 film deposition, which can act as nucleation seeds to assist crystal growth and decrease the trap defects. Meanwhile, we reveal that bromide ions in CsPbBr3 seeds can diffuse toward atop CsPbI3 film to improve energy level alignment and promote carrier transport after annealing process. In this way, the simultaneous crystal growth regulation and interface engineering are triggered in CsPbI3 PSC by CsPbBr3 seeds. Therefore, a remarkable efficiency of 18.60 % was achieved for the optimized CsPbI3 PSC, and it can maintain 86 % of its initial efficiency after being stored for 500 h in ambient environment with controlled relative humidity (RH) of 10–20 %. Our work demonstrates an interesting method to fabricate high-performance CsPbI3 PSCs to promote their potential commercialization.