Theoretical investigations of optoelectronic and transport properties of halide based K2YAuX6 (X = Cl, Br) double perovskites

Intriguing optoelectronic and transport properties with huge compositional range and structural stability make double perovskites interesting for energy harvesting technologies. Here we theoretically investigate the structural, optical, mechanical, and transport properties of K2YAuX6 (X = Cl, Br) double perovskites using the WIEN2K code. Based on the calculated values of the tolerance factor and enthalpy of production, the thermodynamic and structural stability is affirmed. The ductile nature of these compositions is revealed in the computation of Poisson's ratio (>0.26) and Pugh's (1.75) ratio. The involvement of s-states of K, p-states of Cl/Br, and d-states of Y and Au in the formation of valence and conduction band edges is exhibited from the density of state plots. Using the Tran-Blaha mBJ potential and spin-orbital coupling, the energy bandgap value for K2YAuCl6 and K2YAuBr6 is reported as 3.20, and 2.70 eV, respectively, which is suitable for the fabrication of light-emitting diodes. Optical behavior is further explored regarding complex dielectric constant, refractive index, optical conductivity, optical loss, and absorption factor. The small value of thermal conductivity with large value of electrical conductivity, Seebeck coefficient, power factor, and figure of merit revealed the potential of these materials for the fabrication of light-emitting diodes and thermoelectric generators.