Abstract: The crystalline quality of CsPbBr₃ thin film was improved by using steam atmosphere annealing method. The perovskite film was prepared using a multi-step spin-coating process, where a layer of PbBr₂ was first spin-coated followed by two layers of CsBr. The spin-coated films were then annealed in air, methanol vapor, and N, N-dimethylformamide (DMF) vapor. The morphology and structure of the thin films were analyzed using scanning electron microscopy(SEM) and X-ray diffraction (XRD). The experimental results show that annealing in methanol vapor atmosphere can increase the grain size of the perovskite and improve its crystallinity. Then, the CsPbBr₃ thin film was used as the absorber layer in a solar cell structure consisting of FTO/c-TiO₂/m-TiO₂/CsPbBr₃/Carbon. The photovoltaic properties were characterized using current-voltage(J-V) measurements, external quantum efficiency(EQE) and electrochemical impedance spectroscopy (EIS). The results show that the solar cell fabricated using the CsPbBr₃ thin film annealed in methanol vapor atmosphere exhibits a significantly improved power conversion efficiency, which increases from 5.05% to 7.32%. This improvement is mainly attributed to the lower defect density and higher charge carrier transport properties of the perovskite thin film.