Study of optoelectronic, thermoelectric, mechanical properties of double perovskites Cs2AgAsX6 (X = cl, br, I) for solar cells and energy harvesting

The double perovskites (DPs) are potential materials to harvest energy from sun and waste heat. Here we theoretically calculated the electronic and optical, and transport characteristics of Cs 2 AgAsX 6 (X = Cl, Br, I) using WEIN2k code. The unit cell of these DPs is taken as cubic (FCC) and their lattice constant increase from 10.35–11.89Å with increasing ionic radius of halogen. The enthalpy of formation (-1.55 to -0.85 eV) are computed to show the thermodynamic existence and factor of tolerance for structural stability. The band structures analysis shows the shifting of band gap (1.71 to 0.90 eV) from visible to infrared region by the replacement of Cl with Br and I. The absorption bands have the peaks at 3.0 eV, 2.5 eV, and 2.0 eV for Cl, Br, and I, respectively which increase their significance for solar cells. The chemical potential and temperature dependent thermodynamic parameters are computed using BoltzTraP code. The large value of electrical conductivity in contrast with thermal conductivity along with high Seebeck coefficient and figure of merit assured the suitability of these compositions for futuristic energy harvesting devices. The mechanical parameters show that the Cl based DP is ductile while Br and I based are brittle. The large Debye and melting temperatures, hardness and ultralow lattice thermal conductivities also increase their importance.