First-principles investigation of optical and thermoelectric properties of Na2InCu(F/Cl)6 double perovskites for energy harvesting devices

Abstract

The structural stability, optical, electronic, and thermoelectric properties of Na${}_2$InCu(F/Cl)${}_6$ double perovskites have been investigated using density functional theory (DFT) with the Tran–Blaha modified Becke–Johnson potential and spin–orbit coupling (TB-mBJ + SOC). The structural analysis confirms the stability of the cubic phase for both compounds, with lattice parameters of 8.47 Å for Na${}_2$InCuF${}_6$ and 10.07 Å for Na${}_2$InCuCl${}_6$. The electronic properties reveal semiconducting behavior with a direct band gap for both materials. Optical parameters, including absorption coefficients, refractive index, and reflectivity, are calculated and analyzed. The band gaps, along with favorable optical properties such as high absorption coefficients, indicate the potential of these compounds for solar cell and optoelectronic applications. Thermoelectric properties, including electrical conductivity, thermal conductivity, and the Seebeck coefficient, are evaluated to determine their contribution to the figure of merit (ZT). The room-temperature ZT values highlight the suitability of Na${}_2$InCu(F/Cl)${}_6$ for thermoelectric applications.