Large-area, highly uniform CsxFA1−xPbI3−yBry mixed cation perovskite films were prepared by a facile vapor-solid reaction method. In this method, CsBr and PbI2 were first deposited via thermal evaporation, and then exposed to FAI/FACl vapor to form the CsxFA1−xPbI3−yBry perovskite. With the incorporation of CsBr, the crystallinity of the FAPbI3 perovskite could be significantly improved. Meanwhile, the FACl vapor could accelerate the growth rate of the CsxFA1−xPbI3−yBry perovskite in the vapor-solid reaction process. By optimizing the content of Cs and the ratio of FACl/FAI, we obtained high quality, pin-hole free Cs0.24FA0.76PbI3−yBry films. Based on these films, the small sized perovskite solar cells (PSCs) reached a champion power conversion efficiency (PCE) of 17.29%. Without encapsulation, the device with the Cs0.24FA0.76PbI3−yBry perovskite showed much better moisture and thermal stability in comparison to that with the pristine FAPbI3 perovskite. Furthermore, we also fabricated PSC modules with a size of 8 × 8 cm2 and achieved a PCE of 12.24%, indicating that such a vapor-solid reaction method has a certain superiority in the manufacture of large-scale PSCs.