Narrowband Emitting Tin Dion–Jacobson Perovskites through Systematic Spacer Cation Design to Suppress Metal Lone-Pair Anisotropy

Here, we systematically study 13 DJ Pb/Sn iodide perovskite pairs with identical diammonium spacer cations, including four newly synthesized Sn phases, to seek structure–property trends.

We show that narrow and symmetric PL of Pb perovskites alone does not predict similarly favorable emission from Sn analogues. Instead, Sn DJ perovskites with narrow and symmetric PL share a structural motif defined by crystallographically equivalent perovskite pockets and minimal metal off-centering distortion, which can be achieved by symmetric spacer cations. First-principles calculations together with symbolic regression quantitatively connect this motif to reduced anisotropy of the Sn²⁺ lone pair expression and smaller excited-state structural reorganization, consistent with suppressed vibronic broadening of PL peaks.