Improved thermoelectric, thermodynamic, and optical properties performance of double perovskites A2SnBr6 (A = Cs,K,Rb) from first-principles calculations

Recent studies have shown that the double perovskites A(2)SnB(r)6 (A = Cs, K, Rb) is a promising material due to their potential application prospect in new conversion technologies such as photovoltaic thermal radiation fields. In this work, we have investigated the thermoelectric and thermodynamic properties of double perovskites A(2)SnBr(6) within density functional theory via the full-potential linearized augmented plane wave quasi-harmonic Debye approximation with the wien2k computational code. For the optoelectronic properties, our calculated results found to have direct band gaps. The structural study reveals the cubic phase stability at high temperature T > 400K. Furthermore, the thermoelectric parameters such as the Seebeck coefficient (S-b), thermal conductivity (k), electrical conductivity (sic), figure of merit (ZT), and power factor (PF) of vacancy-ordered double perovskites obtained with the use of the BoltzTraP code. Confirming the semiconductor nature of A(2)SnBr(6) compounds as predicted by their electronic properties. The predicted maximum value ZT is about 0.997 in the p-type region and 0.995 in the n-type region. The Furthermore, optical properties are computed with band gaps 2.407eV, 2.332 eV and 2.220 eV for Cs2SnBr6, Rb2SnBr6 and K2SnBr6 respectively).These materials absorb light in ultra violet region and can be used as absorber of UV-rays. Also materials are suitable for thermoelectric power generator applications. Finally, the thermodynamic parameters such as Gruneisen parameter, Entropy S of a system, Heat capacity have been predicted using quasi-harmonic approximation. We have computed pressure and temperature dependent thermodynamic parameters for A(2)SnBr(6) in the temperature range of 0 K-289.15 K and pressure range of 0 GPa-25 GPa with a step size of 5 GPa.