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Mixed tin (Sn)–lead (Pb) perovskites with high Sn content exhibit low bandgaps suitable for fabricating the bottom cell of perovskite-based tandem solar cells. In this work, we report on the fabrication of efficient mixed Sn–Pb perovskite solar cells using precursors combining formamidinium tin iodide (FASnI₃) and methylammonium lead iodide (MAPbI₃). The best-performing cell fabricated using a (FASnI₃)_0.6(MAPbI₃)_0.4 absorber with an absorption edge of ∼1.2 eV achieved a power conversion efficiency (PCE) of 15.08 (15.00)% with an open-circuit voltage of 0.795 (0.799) V, a short-circuit current density of 26.86(26.82) mA/cm², and a fill factor of 70.6(70.0)% when measured under forward (reverse) voltage scan. The average PCE of 50 cells we have fabricated is 14.39 ± 0.33%, indicating good reproducibility.