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 n = 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 in situ 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.