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1,4‐butanediamine (BEA) is incorporated into FASnI₃ (FA=formamidinium) to develop a series of lead‐free low‐dimensional Dion–Jacobson‐phase perovskites, (BEA)FA_n−1Sn_nI_3n+1. The broadness of the (BEA)FA₂Sn₃I₁₀ band gap appears to be influenced by the structural distortion owing to high symmetry. The introduction of BEA ligand stabilizes the low‐dimensional perovskite structure (formation energy ca. 10⁶ j mol⁻¹), which inhibits the oxidation of Sn²⁺. The compact (BEA)FA₂Sn₃I₁₀ dominated film enables a weakened carrier localization mechanism with a charge transfer time of only 0.36 ps among the quantum wells, resulting in a carrier diffusion length over 450 nm for electrons and 340 nm for holes, respectively. Solar cell fabrication with (BEA)FA₂Sn₃I₁₀ delivers a power conversion efficiency (PCE) of 6.43 % with negligible hysteresis. The devices can retain over 90 % of their initial PCE …