Influence of spin-coating methods on the properties of planar solar cells based on ambient-air-processed triple-cation mixed-halide perovskites

• CsFAMAPbIBr perovskites are fully synthesized in ambient air atmosphere. • Effect of two different spin coating strategies, static and dynamic spin coatings, are discussed. • Dynamic spin-coated CsFAMAPbIBr based device exhibit a higher PCE of 19.70% than the counterpart. • Unencapsulated PSCs based on dynamic spin-coated CsFAMAPbIBr exhibited improved long-term stability. Highly efficient perovskite solar cells based on triple-cation mixed-halide perovskite (CsFAMAPbIBr) require a strictly controlled environment such as a N 2 -filled glove box and/or a dry room due to the instability of formamidinium (FA) ions in humid environment. Furthermore, sufficient knowledge regarding the detailed ambient air processing techniques is lacking. Therefore, the processing of efficient CsFAMAPbIBr-based solar cells in ambient air atmosphere is very challenging and essential for low-cost commercialization. Herein, the effect of different coating methods, static spin coating and dynamic spin coating, on the fabrication of two-step ambient-air-processed CsFAMAPbIBr films and the photovoltaic properties of CsFAMAPbIBr-based planar solar cells is presented. Different compositions and morphologies of CsFAMAPbIBr are obtained because of the different reaction times between the pre-deposited PbI 2 -CsI layer and the secondary deposited organic materials (FAI/MABr/MACl) in static and dynamic spin-coating methods, which lead to differences in Ostwald ripening and ion exchange in ambient-air atmosphere, thereby substantially affecting the power conversion efficiency (PCE) and stability of the fabricated solar cells. Planar solar cells based on dynamic-spin-coated CsFAMAPbIBr exhibit a higher PCE of 19.70% (17.27% ± 1.25%), than those based on static-spin-coated CsFAMAPbIBr, whose PCE was 16.01% (9.89% ± 2.34%).