Liquid-like Free Carrier Solvation and Band Edge Luminescence in Lead-Halide Perovskites

TL;DR

This study reveals a temperature-dependent luminescence shift in lead-bromide perovskites, explained by dielectric solvation theories, bridging liquid-like and solid-state behaviors in these materials.

Contribution

It introduces a dielectric solvation model based on classical relaxation to explain the luminescence behavior in lead-halide perovskites, linking vibrational spectra with electronic properties.

Findings

Luminescence Stokes shift varies strongly with temperature.

Dielectric solvation models reproduce experimental spectra.

Anharmonic LO phonon at 20 meV influences dielectric response.

Abstract

We report a strongly temperature dependent luminescence Stokes shift in the electronic spectra of both hybrid and inorganic lead-bromide perovskite single crystals. This behavior stands in stark contrast to that exhibited by more conventional crystalline semiconductors. We correlate the electronic spectra with the anti-Stokes and Stokes Raman vibrational spectra. Dielectric solvation theories, originally developed for excited molecules dissolved in polar liquids, reproduce our experimental observations. Our approach, which invokes a classical Debye-like relaxation process, captures the dielectric response originating from an anharmonic LO phonon at about 20 meV (160 cm-1) in the lead-bromide framework. We reconcile the liquid-like picture with more standard solid-state theories of the Stokes shift in crystalline semiconductors.