FA1−xCsxPbI3 solid solution films are prepared as light harvesters for perovskite solar cells by a spray reaction. Cs+ ions can improve the quality of the light harvester film, and the average PCE of devices increases from 11.3% for FAPbI3 to 14.2% for FA0.9Cs0.1PbI3. Moreover, FA0.9Cs0.1PbI3-based devices exhibit remarkable improvement on humidity stability.
