Study of optoelectronic, transport, and mechanical aspects of lead-free double perovskites Rb2AgTlX6 (X = Cl, Br) for green energy applications

The lift side represents the absorption coefficient with a large absorption band in the visible region, and the lif side shows the polyhedral crystal structure of studied double perovskites. [Display omitted] •Stable, cheap, and significant for solar cells.•The absorption bands lie in the visible region.•Ultralow lattice thermal conductivity.•Minimal reflection and optical loss. The double perovskites are emerging candidates for renewable energy applications. This work uses the extensive density functional theory (DFT) method to investigate the structural, optoelectronic, transport, and mechanical properties of Rb2AgTlX6 (X = Cl, Br). The thermal and structural stabilities of Rb2AgTlX6 (X = Cl, Br) are investigated through formation energy and tolerance factorevaluation.The Rb2AgTlCl6 and Rb2AgTlBr6 have direct band gaps of 1.61 eV and 1.08 eV. The reported band gap reduction is associated with the p-d hybridization of cations and anions. Investigating optical characteristics yields important insights via the dielectric constant ε(ω), refractive index n(ω), absorption α(ω), and reflectivity R(ω). The ability to absorb light in visible and ultraviolet spectra as demonstrated by optical characteristics highlights the potentialof Rb2AgTlX6 for solar cell technology. In addition, the significant electrical conductivity and Seebeck coefficient led to a notable reduction in heat conductivity and figure of merit values of 0.68 and 0.67 at higher temperatures. Elastic parameters, Pugh’s, and Passion’s ratios are studied to confirm materials’ mechanical stability and nature. The studied materials have been found mechanically stable and brittle. Together, our findings demonstrate the distinctive and intriguing features of Rb2AgTlX6 (X = Cl, Br) are suitable for cost-effective energy conversion applications.