The performance of FAPbI3-based perovskite solar cells (PSCs) has been drastically improved with a photoelectric conversion efficiency (PCE) of 25.7%, showing attractive application potential. To achieve higher efficiency and longer-term stability of PSCs, a large number of passivation methods are used to inhibit Pb and I defects of FAPbI3 films. In this study, we developed a facile method to suppress the residual PbI2 of perovskite films and the related defects efficiently by a two-step spin-coating process, which prominently improves the carrier lifetime of α-FAPbI3 films (from 459 ns to 1346 ns). In addition, the morphology and crystallization characteristics of the films were also significantly improved, and the grains grew up to 1 μm. The efficiency of FAPbI3-based PSCs fabricated by this method reached 22.64%.