Fig. 1. Crystal structure, electronic bands, and PL spectra of 2D Dion–Jacobson perovskites.

a, b Crystal structures of 2D Dion–Jacobson perovskites, (3AMP)PbI₄ and (4AMP)PbI₄, together with the chemical structures of the organic cations. c, d Electronic bands and total and projected density of states (PDOS) of (3AMP)PbI₄ and (4AMP)PbI₄ calculated at the DFT HSE06 level with spin-orbit coupling (SOC). Enlarged electronic bands near the valence band maximum and conduction band minimum are shown in the insets. e, f Temperature-dependent PL spectra of the (3AMP)PbI₄ and (4AMP)PbI₄ films, together with the time-resolved PL decays for the emission from the (3AMP)PbI₄ film at 565 nm and the emission from the (4AMP)PbI₄ film measured at 560 nm and room temperature. The solid lines represent fits to a biexponential decay function. Note that the observed spikes in (e) could be due to the presence of film irregularities that lead to small reflections inside the film.