Ab-Initio based investigation of the optoelectronic, transport, mechanical properties of vacancy-ordered double perovskites A2PtI6 (A = Na, Li): An emerging class of solar cell and thermoelectric materials

In this study, the structural, thermoelectric, mechanical, electrical, and optical properties of vacancy-ordered double perovskites A2PtI6 (A = Li, Na) have been investigated using density functional theory-based methods. As per the findings, both the materials are stable as confirmed by their calculated formation and cohesive energies. Each compound's ductility and mechanical stability have been verified. The values of band-gap are computed using dissimilar exchange correlation functions PBE-GGA, mBJ, mBJ + SOC. The results show that A2PtI6 (A = Na, Li) are semiconducting material possessing indirect bandgaps having the values of 0.344 eV and 0.347 eVs through PBE-GGA and 0.954 eV and 1.034 eVs by mBJ approximations. After SOC corrections, the band gap values for Li2PtI6 and Na2PtI6 are found to be 0.820 eV and 0.880 eVs respectively. Similarly, the optical properties like dielectric function, reflectivity, absorption coefficient, loss functions are also computed to explore the optoelectronics applications for these compounds. We also assess the thermoelectric parameters that result in advantageous thermoelectric performance, such as power factors, Seebeck coefficients, and electronic & lattice thermal conductivities. At 1200 K, Li2PtI6 and Na2PtI6 attain maximum figure of merit (ZT) of 0.58 and 0.50, respectively. These outcomes underscore the materials' potential for use in thermoelectric devices and solar cells, highlighting their efficacy at high temperatures.