Regulating Pb off-centering distortion for white-light emission in 2D halide perovskites

Efficient tuning of structural distortion is an attractive approach for regulating self-trapped excitons emission properties of two-dimensional halide perovskites. Nevertheless, it remains elusive as to how the structural distortion is related with such emission. Here, we elucidate the relationship between structural distortion and the emission behavior of self-trapped excitons in two-dimensional lead bromide perovskites (R-NH₃)₂PbBr₄ (where R is the cyclic carbon group). We reveal that rather than the octahedral tilting distortion, the lone pair activity-induced Jahn-Teller distortion plays a significant role in self-trapped excitons emission. Consequently, with growing ring size of cyclic organic cation, the increased Jahn-Teller distortion results in a larger relative self-trapped excitons emission due to the enhanced short-range Holstein electron-phonon coupling strength. Our work clarifies the controversy of the structural distortion correlation on self-trapped excitons emission and provides valuable insights for structural engineering in white-light emitting applications of two-dimensional perovskites.