Abstract To improve the photovoltaic performance of the perovskite solar cells, it is necessary to reduce the density of surface defect for perovskite film with smooth surface. In this paper, we demonstrate a DMSO/CB mixed vapor annealing process to fabricate high-performance planar perovskite solar cells. The mixed vapor annealing treatment can significantly enhance the crystallization of perovskite film, leading to less crystal surface defects, effective charge-separation and the electron transport rate at the perovskite interface. Finally, the efficiency and reproducibility of the cells has been greatly improved. The power conversion efficiency (PCE) improved from 16.6% to 18.4% under AM 1.5G 100 mW·cm−2 irradiation. We anticipate that the mixed vapor annealing treatment will become a promising crystallization method for the fabrication of high performance PSCs in the future commercialization.