Theoretical Investigation of the Lead-Free K₂InBiX₆ (X = Cl, Br) Double Perovskite Compounds Using Ab Initio Calculation

In this study, we employ the full potential linearized augmented plane wave technique based on density functional theory applied in the WIEN2k code to examine the structural, elastic, electrical, optical, and thermoelectric properties of double perovskite K₂InBiX₆ (X = Cl, Br) compounds. Tolerance factor, formation energy, and phonon dispersion all confirm structural stability. Using the exchange correlation generalized gradients approximation, and modified Becke–Johnson, the electronic characteristics have been calculated. The calculated bandgaps using TB-mBJ potential for K₂InBiX₆ (X = Cl, Br) compounds are 1.81 and 1.29 eV, respectively, indicating that the compounds under study are semiconductors. Both materials exhibit thermodynamic stability, as evidenced by an analysis of their elastic and mechanical properties. We estimated the optical properties in terms of the real and imaginary parts of the dielectric function, refractive index, reflectivity and absorption coefficient reflecting their application in photovoltaic and optoelectronic devices. In the temperature range 200–800 K, the thermoelectric properties of the compounds, such as electrical conductivity, Seebeck coefficient, thermal conductivity, and power factor, have been analyzed. The compound has a positive Seebeck coefficient in this temperature range, indicating that holes are the majority charge carriers and that the material is p-type. The high-power factor of studied compounds suggests its potential application in thermoelectric devices.