Determining Exciton Binding Energy and Reduced Effective Mass in Metal Tri-Halide Perovskites from Optical and Impedance Spectroscopy Measurements

TL;DR

This paper introduces a new method to accurately determine exciton binding energy and reduced effective mass in halide perovskites by incorporating polarization effects and using optical absorption data, validated against other techniques.

Contribution

The authors develop a novel approach combining Elliott's Band Fluctuations model and Pollmann-Buttner's exciton-polaron model to measure key electronic properties in perovskites, accounting for polarization effects.

Findings

Excellent agreement with magnetoabsorption measurements.

Robust method applicable to various halide perovskites.

Enhanced understanding of electron-phonon interactions in polar materials.

Abstract

Accurate determination of the exciton binding energy and reduced effective mass in halide perovskites is of utmost importance for the selective design of optoelectronic devices. Although these properties are currently determined by several spectroscopic techniques, complementary theoretical models are often required to bridge macroscopic and microscopic properties. Here, we present a novel method to determine these quantities while fully accounting for polarization effects due to carrier interactions with longitudinal optical phonons. Our approach estimates the exciton-polaron binding energy from optical absorption measurements using a recently developed Elliott based Band Fluctuations model. The reduced effective mass is obtained via the Pollmann-Buttner exciton-polaron model, which is based on the Frohlich polaron framework, where the strength of the electron-phonon interaction arises from changes in the dielectric properties. The procedure is applied to the family of perovskites ABX3 (A = MA, FA, Cs; B = Pb; X = I, Br, Cl), showing excellent agreement with high field magnetoabsorption and other optical-resolved techniques. The results suggest that the Pollmann-Buttner model offers a robust and novel approach for determining the reduced effective mass in metal tri-halide perovskites and other polar materials exhibiting free exciton bands.