Bismuth-based perovskites are an important class of materials in the fabrication of lead-free perovskite solar cells. Bi-based Cs₃Bi₂I₉ and CsBi₃I₁₀ perovskites are getting much attention due to their appropriate bandgap values of 2.05 eV and 1.77 eV, respectively. However, the device optimisation process plays a key role in controlling the film quality and the performance of perovskite solar cells. Hence, a new strategy to improve crystallization as well as the thin film quality is equally important to develop efficient perovskite solar cells. Herein, an attempt was made to prepare the Bi-based Cs₃Bi₂I₉ and CsBi₃I₁₀ perovskites via the ligand-assisted re-precipitation approach (LARP). The physical, structural, and optical properties were investigated on perovskite films deposited by the solution process for solar cell applications. Cs₃Bi₂I₉ and CsBi₃I₁₀-based perovskite-based solar cells were fabricated using the device architecture of ITO/NiO_x/perovskite layer/PC₆₁BM/BCP/Ag. The device fabricated with CsBi₃I₁₀ showed the best power conversion efficiency (PCE) of 2.3% with an improved fill factor (FF) of 69%, V_OC of 0.79 V, and J_SC of 4.2 mA cm⁻² compared to the Cs₃Bi₂I₉-based device which showed a PCE of 0.7% with a FF of 47%, V_OC of 0.62 V and J_SC of 2.4 mA cm⁻².