Bismuth‐based perovskites are promising candidates for lead‐free and air‐stable photovoltaics. However, the poor surface morphologies and high exciton binding energy of the bismuth‐based perovskites have limited their performances. Herein, the density functional theory calculations unveil that CsBi₃I₁₀ possesses favorable optoelectronic properties such as a narrow bandgap, a small effective mass, and relatively high electron mobility. To tackle the poor‐surface morphology problem, the high‐quality CsBi₃I₁₀ films are fabricated via gas‐assisted spin‐coating and solvent vapor annealing in ambient conditions. Using the [6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM) as the electron acceptor, an optimized inverted CsBi₃I₁₀/PCBM bulk‐heterojunction structure enables a high power conversion efficiency of 1.18% among the CsBi₃I₁₀‐based perovskite solar cells. The approach exemplified in this work could be useful for designing the high‐performance Bi‐based lead‐free perovskite solar cells.