Oxysulfide Perovskites: Reduction of the Electronic Band Gap of RbTaO3 by Sulfur Substitution to Enhance Prospective Solar Cell and Thermoelectric Performances

TL;DR

This study investigates how sulfur substitution in RbTaO3 alters its properties, notably reducing the band gap to improve its potential for solar and thermoelectric applications, supported by comprehensive computational analysis.

Contribution

It provides detailed computational insights into structural, electronic, optical, and thermodynamic changes due to sulfur substitution in RbTaO3, highlighting enhanced solar and thermoelectric potential.

Findings

Band gap decreases from 2.717 eV to 1.438 eV with S substitution.

RbTaO2S exhibits high absorption coefficient (~10^6 cm^-1).

S substitution reduces phonon thermal conductivity, improving thermoelectric performance.

Abstract

In this study, the effects of sulfur substitution on the structural, mechanical, electronic, optical, and thermodynamic properties of RbTaO3-xSx have been investigated using the WIEN2k code in the framework of density functional theory (DFT). The cubic phase of RbTaO3 transforms to tetragonal for RbTaO2S and RbTaOS2, the later transforms again to a cubic phase with added sulfur for RbTaS3. The results showed that substituting S for O anions in RbTaO3 effectively decreased the band gap from 2.717 eV to 1.438 eV, 0.286 eV, and 0.103 eV for the RbTaO3,RbTaO2S, RbTaOS2, and RbTaS3 compounds, respectively. The optical constants such as dielectric constants, refractive index, absorption coefficient, photoconductivity, reflectivity and loss function have been calculated and analyzed. The elastic constants and moduli, and their anisotropic nature were also investigated. Finally, the Debye temperature, thermal conductivity, melting temperature, specific capacities and thermal expansion coefficients were computed and analyzed using established formalisms. The reduced band gap (1.438 eV) and high absorption coefficient (~106 cm-1) of RbTaO2S makes it suitable for solar cell applications and for other visible light devices. Reduction of the band gap and phonon thermal conductivity owing to Ssubstitution is expected to enhance thermoelectric performances of the S-containing phases