A balanced cation exchange reaction toward highly uniform and pure phase FA1-xMAxPbI3 perovskite films

Unlike traditional MAPbI(3), methods for large scale fabrication of high quality FA based perovskite films are still lacking. In this paper, the organic cation exchange temperature is optimized toward the formation of highly uniform FA based perovskite films. Under optimized conditions, the cation diffusion speed within the perovskite film is extremely enhanced and the time constant is reduced similar to 20 times. The shortened dipping time and mild reaction conditions can efficiently restrict the undesirable phase transition and preserve the film morphology. Fundamental insight into this solid-liquid reaction has been obtained by combining photophysical, XRD and SEM characterizations. The optimized FA(x)MA(1-x)PbI(3) with x approximate to 0.75 presents the highest efficiency of 15.5% with less hysteresis.