First-principle’s calculations to investigate structural, electronic, mechanical, optical, and thermoelectric properties of halide double perovskites K2InScX6 (X = Cl, Br, and I) for thermoelectric and optoelectronic applications

Physical properties of double perovskites K₂InScX₆ (X = Cl, Br, and I) are investigated using density functional theory (DFT) with generalized gradient approximation (GGA) and perdew-burke-ernerhof (PBE) exchange co-relational functional. Structural stability is confirmed through geometry optimization. Band gaps are calculated using Trans Blaha-modified Becke-Johnson (TB-mBJ) potential and GGA-PBE methods. The obtained band gaps have direct nature. The structural stability has also been confirmed by calculating enthalpy formation (ΔH_f), cohesive energy (E_coh), stiffness coefficients (C_ij), tolerance (τ_G) and octahedral factor (µ). Two materials K₂InScCl₆, and K₂InScBr₆ are ductile and one is K₂InScI₆ brittle. The optical parameters inferred that the maximum absorption of photon energy lies within the visible and ultraviolet regions enabling their use in UV photodetectors and optoelectronics, where light absorption is important for performance. The thermoelectric (TE) parameters like Seebeck coefficient, thermal and electrical conductivity, carrier concentration, power factor and figure of merit ZT parameters are calculated and ZT values are 0.75, 0.94, and 0.91 for K₂InScCl₆, K₂InScBr₆, and K₂InScI₆ at room temperature. These results enable the development of more stable, and high-conversion efficiency devices for TE applications such as thermo-electric power generators.