Using the pure N,N-dimethyl formamide, pure dimethyl sulfoxide and mixed solvents with different proportion as precursor solvent, respectively, the perovskite thin film samples were prepared. The samples were divided as two sets, one set was processed by thermal annealing in N2 atmosphere, while the other set was processed by solvent annealing in dimethyl sulfoxide vapor atmosphere. The microstructure and optoelectronic properties of the samples were systematically analyzed. The results show that, compared with the thermal annealing, the grain size and uniformity of samples can be significantly improved by solvent annealing, which reduces volume fraction of grain boundaries or interfaces in the films. By solvent annealing and mixed solvents, the absorption and utilization ratio of visible light are enhanced, the morphology is improved, and the crystallization quality is optimized. The increasing of photoluminescence intensity indicates that the defect densities of thin film are reduced. Thin film solar cells were fabricated using the optimized perovskite film as the absorber layer, and a conversion efficiency of 15.7% was achieved.