Exploring direct band gap engineering in chloro-elpasolite Cs2BInCl6 (B=Ag and Au): A comprehensive study of structural, elastic, optoelectronic and thermoelectric properties

In this investigation, an analysis was conducted on the stability, structural, electronic, optical, and thermoelectric properties of the halide double perovskites (HDPs) Cs2BInCl6 where B=Ag and Au. Applying the FP-LAPW approach, which is a subset of density functional theory (DFT), the study was performed employing the Wien2k code package. The most stable configuration corresponds to the cubic Fm͞3m (N°225) symmetry in a nonmagnetic (NM) state, as determined through the analysis of optimal structural parameters for both materials. The examination of the electronic features illustrates a semiconductor behavior characterized by a direct band gap at the Γ-Γ direction, with values of 3.245 eV for Cs2AgInCl6 and 2.052 eV for Cs2AuInCl6, closely mirroring experimental observations. The optical computations demonstrate an absorption coefficient within the visible spectrum that is almost zero and exceeding 1.6x104 cm-1 in the Extreme Ultraviolet (EUV) range. Moreover, the high reflectivity of the materials, reaching a peak of 55% for Cs2AgInCl6 and 40% for Cs2AuInCl6 at 17.5eV (70.85 nm) in EUV region, indicates a promising potential for utilization in optoelectronics, particularly in the UV and EUV sectors. Additionally, the assessment of thermoelectric performance involved the computation of thermoelectric properties. Both perovskites exhibit elevated electrical conductivity, low thermal conductivity, an increased Seebeck coefficient, and a higher figure of merit, positioning them as favorable candidates for thermoelectric applications.