Low-Dimensional Dion-Jacobson-Phase Lead-Free Perovskites for High-Performance Photovoltaics with Improved Stability.

1,4-butanediamine (BEA) is incorporated into FASnI3 (FA=formamidinium) to develop a series of lead-free low-dimensional Dion-Jacobson-phase perovskites, (BEA)FAn-1 Snn I3n+1 . The broadness of the (BEA)FA2 Sn3 I10 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)FA2 Sn3 I10 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)FA2 Sn3 I10 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 N2 environment.