First-principles calculations to investigate mechanical, thermoelectric and optical performance of inorganic double perovskites Rb2CuBiX6 (X = Cl, Br, I) for energy harvesting

The double perovskites Rb2CuBiX6 (X = Cl, Br, I) are studied for thermoelectric and optoelectronic applications for energy harvesting. The confirmation of thermodynamic constancy has been reported by formation energy and tolerance factor by structural stability. The lattice constant increases and bulk modulus decreases by changing the halogen ions (Cl, Br, I). The ductile behavior, large Debye and Kelvin temperatures along hardness and ultralow values of lattice thermal conductivity are calculated from elastic constants. The TB-mBJ potential has been used to modify the band gaps from 1.18 to 0.68 eV by shifting of halogen ions Cl to I. The optical characteristics are analyzed by absorption, dispersion, refractive index, and reflection of light energy. In addition to above, the transport characteristics are analyzed by Seeback coefficient, electronic and thermal conductivities. The figure of merit calculations shows the excellent thermoelectric performance of studied DPs.