Effect of reaction time on the morphology and efficiency of ambient-air-processed CsFAMAPbIBr triple cation-mixed perovskite solar cells

•CsFAMAPbIbr perovskites were synthesized using a sequential two-step deposition method in ambient-air condition.•The time of reaction between PbI2-CsI and FAI/MABr/MACl played an important role in the final morphologies and pinholes.•With a reaction time of 5 s, the ambient-air processed planar device achieved a PCE of 16.01%. The mixed-cation halide perovskites containing formamidinium (FA) are vulnerable to moisture due to easy bonding of FA moieties with H2O. Thus, a strict humidity controlled environment is indispensable for the highest efficiency CsFAMAPbIBr perovskites synthesis, which hinders the development of perovskite manufacturing in ambient atmosphere. In addition, the morphological evolution of CsFAMAPbIBr perovskites in a humid environment and consequent photovoltaic performance is important for understanding ambient air processed mixed perovskite solar cells, but few have been reported. Here, CsFAMAPbIBr perovskites were synthesized in an ambient air atmosphere by a sequential two-step deposition method. The effect of the reaction time is focused to corelate morphological variation and the resultant photovoltaic properties. Using the optimal reaction time of 5 s, CsFAMAPbIBr based planar solar cells with a power conversion efficiency (PCE) of 16.01% were achieved.