DFT Investigations on the Thermoelectric, Electronic, Optoelectronic, Elastic, and Structural Properties of K 2 NaTIX 6 (X=I, Br, and Cl) Double Perovskite

Abstract Despite Pb-based perovskites, sodium-based halide double perovskites (HDPs) provide a bright future for the production of safe solar and thermal energy conversion of devices. These compounds are highly durable, and their elements are non-toxic. So, the present study investigates the thermoelectric, electronic, optoelectronic, elastic, and structural properties of K2NaTIX6 (X = I, Br, and Cl) double perovskite compounds derived from halides using Density Functional Theory (DFT). Investigated compounds are grouped as cubic, and as the halogens are substituted from chlorine to iodine their structural parameter increases. The structural stability is verified through the calculation of the, enthalpy of formation, Pugh's ratio and tolerance factor. The ductile nature is confirmed by Pugh’s ratio of compounds. The halide compounds under investigation all have a direct band gap (3.52, 2.14, and 0.72 eV), granted that the valence and conduction band maxima and minima have the same nature, which results to higher effective mass values. The present investigation focuses on analyzing the refractive index, absorption of light energy, optical loss, and polarization across the entire energy range from 0 to 8 eV. The spectral characteristics suggest that the studied HDPs have the ability to be employed in optoelectronic and photovoltaic devices because of the visible and ultraviolet spectra absorption occurring in this region. The high figures of merit (0.74–0.75) resulting from the calculated power factor and thermal conductivity indicate that these compositions have the capacity to function as thermoelectric devices. These investigations offer a profound comprehension of these materials for their further employment.