Computational investigation on lead-free halide double perovskites <i>Cs</i> ₂ <i>BiAuX</i> ₆ (X = Cl, Br) for optoelectronic, and thermoelectric devices

Abstract In this work, we explore the lead-free inorganic double perovskites Cs 2 BiAuX 6 (X = Cl, Br) for optoelectronic and waste heat recovery systems, using density functional theory. The self-consistent field calculations were performed using various exchange-correlation potentials that include LDA, WC-GGA, PBE-GGA, and TB-mBJ. Electronic band structures show the semiconducting nature of these materials. The band gaps obtained using TB-mBJ are 1.74 eV , and 0.84 eV respectively for Cs 2 BiAuX 6 (X = Cl, Br). Furthermore, thermodynamic, optical, and thermoelectric properties were also investigated. The materials are thermodynamically stable, analyzed for temperatures from 0 to 900 K. Optical properties reveal the increase in dielectric constant, refractive index, and reflectivity due to the change of halogen from Cl to Br. Strong absorption peaks acquired in the UV–visible region, along with a high figure of merit, indicate the proposed materials’ potential as good candidates for energy harvesting applications such as optoelectronic and thermoelectric devices.