Optoelectronic properties and lattice thermal conductivity of Cs2CuBiX6 (X = F, Cl, Br, I) double perovskites: Thermodynamic and ab initio approaches

Abstract

In this work, a first-principles method called full potential linearized augmented plane wave (FP-LAPW) within the generalized gradient approach (GGA) is used to investigate potential double free lead halide perovskites applications. The structural and elastic parameters of double perovskites Cs2CuBiX6 (X = F, Cl, Br, I) are investigated, and the results show that these compounds are stable, have a ductile character, and are characterized by a noticeable elastic anisotropy. Lattice thermal conductivity is calculated via Slack's equation for all studied materials, reflecting a good potential for thermoelectric applications. The calculations of the electronic and optical properties are performed using the GGA combined with the modified Becke-Johnson (mBJ) potential with the incorporation of the spin-orbit coupling (SOC). This SO effect allowed us to have correct bandgap behaviour for the Bi states. The studied compounds have large dispersion in their bands and low carrier effective masses. Furthermore, acceptable quality properties such as long diffusion length, tuneable bandgap, high mobility, ambipolar charge transport, and high absorption reinforce these double perovskites and make them even more suitable for photovoltaic applications.