Optoelectronic and thermoelectric response of lead-free halide double perovskites Rb2BiAuX6 (X = Cl, Br, I) for energy storage applications

Abstract

Double perovskite materials garner a lot of attention because of their extraordinarily high conversion efficiency in solar cells. Here, we report a detailed first-principles study on the structural, mechanical, optoelectronic, and thermal characteristics of Rb₂BiAuX₆ (X = Cl, Br, and I) lead-free halide double perovskites. Rb₂BiAuCl₆ exhibits more favorable nature than the other two materials owing to its lowest formation energy. Rb₂BiAuX₆ (X = Cl, Br, and I) possess mechanical stability, supported by their high elastic constants. Interestingly, these double perovskites reveal a semiconductor nature with a band gap of 1.8 eV, 1.12 eV, and 0.61 eV for Rb₂BiAuCl₆, Rb₂BiAuBr₆, and Rb₂BiAuI₆, respectively. The high absorption peaks in their optical spectra confirm their suitability for solar cells applications. Rb₂BiAuCl₆ demonstrates a higher ZT value of 0.78 at 300 K compared to the other two materials. Furthermore, thermodynamics analysis confirm their suitable behavior under varying pressure and temperature. These results suggest the potential of these double perovskites for promising applications in solar cells and thermal devices.