Infrared optical absorption of Frohlich polaron in metal halide perovskites

TL;DR

This paper presents a theoretical study of infrared optical absorption in Frohlich polarons within metal halide perovskites, revealing multiphonon overtones and their dependence on material properties and temperature, aiding in polaron identification.

Contribution

The study introduces a Huang-Rhys model-based approach to identify Frohlich polarons through infrared absorption spectra in perovskites, highlighting multiphonon overtones as a key signature.

Findings

Multiphonon overtones appear at energies matching multiple LO phonons.

Overtone strength depends on electronic distribution and dimensionality.

Overtone order shifts with temperature, indicating carrier mobility effects.

Abstract

The formation of Frohlich polaron in metal halide perovskites, arising from the charge carrierlongitudinal optical (LO) phonon coupling, has been proposed to explain their exceptional properties, but the effective identification of polaron in these materials is still a challenge task. Herein, we theoretically present the infrared optical absorption of Frohlich polaron based on Huang-Rhys model. We find that multiphonon overtones are appeared as the energy of incident photon matches the multiple LO phonons, wherein the average phonon numbers of a polaron can be directly evaluated by the order of the strongest overtone. These multiphonon structures sensitively depend on the scale of electronic distribution in the ground state and the dimensionality of the perovskite materials, which gives the enlightenment for the effective modulation of competing processes between the polaron formation and carrier cooling. Moreover, the order of the strongest overtone shifts to the higher ones with temperature, providing a potential proof of the carriers mobility affected by LO phonons scattering. The present model not only suggests a direct way to verify Frohlich polaron, but also enriches the understanding of the polaron properties in metal halide perovskites.