The perovskite solar cells have demonstrated to be strong competitors for conventional silicon solar cells due to their remarkable power conversion efficiency. However, their structural instability is the biggest obstacle to commercialization. To address these issues, we prepared (CH₃NH₃)_1−x(HC(NH₂)₂)_xPbI₃ (CH₃NH₃ = MA, HC(NH₂)₂ = FA) perovskite alloys that contain ethylammonium (EA, CH₃CH₂NH₃⁺) and benzylammonium (BA, C₆H₅CH₂NH₃⁺) cations with no new additional two-dimensional (2D) perovskite phases. The crystal structures of alloy perovskites exhibit the cubic phase, which decreased the cation disorder and the intrinsic instability compared to 3D MAPbI₃ perovskite. The band gaps of the alloy perovskites are almost the same as the corresponding 3D perovskites, which exhibit a high refractive index, a large absorption coefficient, and paramagnetic properties for the production of high performance photovoltaic devices. After we constructed the solar cell with the configuration of regular (n–i–p) solar cells using the alloy perovskites, the power conversion efficiencies (PCE) of the MA_0.83EA_0.17PbI₃ perovskite solar cell showed the highest efficiency, which was 10.22%, under 1 sun illumination.