Regulating the crystallization behavior of quasi-2D Dion–Jacobson tin perovskites with a non-linear organic spacer

Two dimensional (2D) tin perovskites have received extensive research attention due to their excellent environmental stability and unique charge carrier behaviors. Among them, 2D Dion-Jacobson (DJ) perovskites have been widely studied for their stronger interlayer interactions and higher structural stability. In this work, quasi-linear 4,4'-ethylenedianiline dihydroiodide (EDANI₂) and non-linear 4,4'-methylenedianiline dihydroiodide (MDANI₂) were introduced as organic spacers for quasi-2D DJ tin perovskites with <i>n</i> = 10. Density Functional Theory (DFT) calculations showed that non-linear MDAN²⁺ has a larger dipole moment than EDAN²⁺. Compared with EDAN²⁺, the stronger interaction between non-linear MDAN²⁺ and the tin perovskite induces the formation of tin perovskite films with larger grain sizes and flatter morphology, which improves carrier transport. Meanwhile, the <i>in situ</i> photoluminescence (PL) measurements revealed rapid nucleation and delayed crystallization growth for the MDAN film. Finally, the quasi-2D DJ solar cells with MDANFA₉Sn₁₀I₃₁ achieved a power conversion efficiency (PCE) of 5.62%, which was substantially higher than that of the EDANFA₉Sn₁₀I₃₁ device (4.53%). After being stored under a nitrogen atmosphere for 2000 h, the MDANFA₉Sn₁₀I₃₁ device maintained more than 90% of the initial PCE. This work sheds light on the structural dependence of organic spacers on the crystallization behaviors of 2D lead-free perovskites.