DFT calculations of optoelectronic and thermoelectric properties of K2NaTlX6 (X = Cl, Br, I) halide double perovskites for energy harvesting applications

The DFT approach was employed to investigate the mechanical, optical and thermoelectric properties of double perovskites (DPs) compounds K2NaTlX6 (X = Cl, Br, I). PBEsol-GGA approximation along with birch-Murnaghan equation is used to calculate the lattice constant, other structural and ground state parameters. The structural, thermodynamic and mechanical stability of these compounds was demonstrated by computing tolerance factor, formation energy and Born criteria. Poisson and Pugh ratio are analyzed to describe the brittle or ductile nature of these studied double perovskites compounds. The anion Cl, Br and I-based double perovskites exhibited direct bandgap as determined from band structure calculations. The study further examined the optical absorption and dielectric constant of the compounds across the energy range 0-10 eV confirming their ability to absorb light in the infrared to visible spectrum. Furthermore, the suitability of the studied double perovskites for thermoelectric applications was assessed using BoltzTraP coding. The Seebeck coefficient, electric conductivity and figure of merit were analyzed, suggesting that these compounds hold promise as viable candidates for thermoelectric applications.