Determining exciton binding energy and reduced effective mass in metal tri-halide perovskites from optical and impedance spectroscopy measurements

Accurate determination of the exciton binding energy and reduced effective mass in bulk 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 method to determine these quantities while considering 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 (EBF) model. The reduced effective mass is obtained via the integration of this well-established EBF model with the Pollmann–Büttner exciton-polaron model, which is based on the Fröhlich 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–Büttner model offers an excellent approach for determining the reduced effective mass in metal trihalide perovskites and other polar materials when combined with the EBF optical dispersion model.