First-Principles Investigation of the Structural, Elastic, Electronic, and Optical Properties of α- and β-SrZrS: Implications for Photovoltaic Applications.

Transition metal perovskite chalcogenides are attractive solar absorber materials for renewable energy applications. Herein, we present the first-principles screened hybrid density functional theory analyses of the structural, elastic, electronic and optical properties of the two structure modifications of strontium zirconium sulfide (needle-like α-SrZrS and distorted β-SrZrS phases). Through the analysis of the predicted electronic structures, we show that both α- and β-SrZrS materials are direct band gaps absorbers, with calculated band gaps of 1.38, and 1.95 eV, respectively, in close agreement with estimates from diffuse-reflectance measurements. A strong light absorption in the visible region is predicted for the α- and β-SrZrS, as reflected in their high optical absorbance (in the order of 10 cm), with the β-SrZrS phase showing stronger absorption than the α-SrZrS phase. We also report the first theoretical prediction of effective masses of photo-generated charge carriers in α- and β-SrZrS materials. Predicted small effective masses of holes and electrons at the valence, and conduction bands, respectively, point to high mobility (high conductivity) and low recombination rate of photo-generated charge carriers in α- and β-SrZrS materials, which are necessary for efficient photovoltaic conversion.