Ab initio analysis of structural, optoelectronic, thermoelectric, and elastic characteristics of K2MBiBr6 (M = Na, Ag, and Cu) for green energy

In the current investigation, we have explored the structural, electrical, optical, thermoelectric, and elastic features of potassium(K) based halide double perovskite K2MBiBr6 (M = Na, Ag, Cu) using the WIEN2k code under the framework of density functional theory. Various factors, including negative formation energy, structural optimization, tolerance, and octahedral factors, verify the stability of perovskites. The generalized gradient approximation has been employed to investigate the structural phase and elastic properties. The Tran-Balaha modified Becke-Johnson function has been utilized to precisely evaluate the electronic, optical, and thermoelectric properties. The electronic parameters, such as band gap and density of states revealed that K2NaBiBr6, K2AgBiBr6, and K2CuBiBr6 are semiconductors, with indirect bandgaps of 4.01, 2.36, and 1.26 eV, respectively. For optical properties, the current study has examined characteristics such as energy loss, refractive index, light energy absorption, and polarization through the entire energy spectrum, which ranges from 0 to 8 eV. The BoltzTraP code is used to examine thermoelectric characteristics, revealing maximum ZT values of 0.75, 0.77, and 0.78, respectively. This study further emphasizes the elastic constants of cubic symmetry to figure out the variation between ductile and brittle nature, anisotropy, and the large melting temperature of these materials. The theoretical findings given in the present article have substantial impacts on the future renewable energy sector especially solar cells and electron transport applications.