Ab initio study of the electronic, optical and thermoelectric properties of lead-free double perovskites K2(Se,Te) Br6

[Display omitted] •The physical properties of K2(Se,Te) Br6 have been studied by DFT method.•K2(Se,Te) Br6 materials have showed semiconductor behavior with indirect energy band gap.•We observed high absorption in the visible region, indicating that both halides are suitable for solar cell applications. In this study, the structural stability, electronic, optical, and thermoelectric properties of K2(Se,Te) Br6 halide double perovskites were investigated using first-principles calculations. By applying Born stability and tolerance factor criteria, the structural stability of the compounds was confirmed. Band structure analysis revealed that K2SeBr6 and K2TeBr6 exhibit semiconducting indirect band gaps of 2 eV and 2.42 eV, respectively. Additionally, a study of the optical properties utilizing the dielectric constants indicated that both substances display minimal reflectivity, remaining below 18%, alongside remarkably high absorption coefficients reaching around 105 cm−1 in the visible spectra. Furthermore, the thermoelectric properties were explored through the BoltzTraP simulation package, revealing a Seebeck coefficient and noteworthy electrical conductivity. These outcomes underscore the versatility of these materials, suggesting their potential suitability for various applications such as solar cells and thermoelectric devices.