Impact of Metal ns2 Lone Pair on Luminescence Efficiency in Low-Dimensional Halide Perovskites

TL;DR

This study uses first-principles calculations to reveal how metal ns2 lone pairs influence exciton behavior and luminescence efficiency in low-dimensional halide perovskites, highlighting differences between Sn and Pb compounds.

Contribution

It demonstrates the role of chemically active metal ns2 lone pairs in exciton relaxation, dissociation, and luminescence efficiency in 0D halide perovskites, a novel insight into their photophysical properties.

Findings

Sn2+ lone pair causes larger Stokes shift and structural distortion.

Enhanced Stokes shift reduces energy loss to defects.

Metal cations promote exciton dissociation into polarons.

Abstract

Based on first-principles calculations, we show that chemically active metal ns2 lone pairs play an important role in exciton relaxation and dissociation in low-dimensional halide perovskites. We studied excited-state properties of several recently discovered luminescent all-inorganic and hybrid organic-inorganic zero-dimensional (0D) Sn and Pb halides. The results show that, despite the similarity in ground-state electronic structure between Sn and Pb halide perovskites, the chemically more active Sn2+ lone pair leads to stronger excited-state structural distortion and larger Stokes shift in Sn halides. The enhanced Stokes shift hinders excitation energy transport, which reduces energy loss to defects and increases the photoluminescence quantum efficiency (PLQE). The presence of the ns2 metal cations in the 0D halide perovskites also promotes the exciton dissociation into electron and hole polarons especially in all-inorganic compounds, in which the coupling between metal-halide clusters is significant.