Low-dimensional Dion-Jacobson-phase lead-free perovskites for high-performance photovoltaics with improved stability

1,4-butanediamine (BEA) is incorporated into $FASn{I}_3$ (FA=formamidinium) to develop a series of lead-free low-dimensional Dion-Jacobson-phase perovskites, (BEA)$F{A}_{n-1}S{n}_n{I}_{3n+1}$. The broadness of the (BEA)$F{A}_{2}S{n}_3{I}_{10}$ 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. 10${}^6$ j mol${}^{-1})$, which inhibits the oxidation of $S{n}^{2+}$. The compact (BEA)$F{A}_{2}S{n}_3{I}_{10}$ 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)$F{A}_{2}S{n}_3{I}_{10}$ delivers a power conversion efficiency (PCE) of 6.43 % with negligible hysteresis. The devices can retain over 90 % of their initial PCE after 1000 h without encapsulation under $N_2$ environment. (© 2020 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)