A Density Functional Theory Exploration of Cs₂B′B″I₆ (B′B″: BeCa, BeSr, GeCd, GeBe, GeMg) Halide Double Perovskites for Optimal Solar Cell and Renewable Energy Applications

Abstract

A comprehensive investigation into the structural, elastic, optoelectronic, and thermoelectric properties of Cs2B′B″I6 halide double perovskites (DPs), where B′B″ represents various combinations, including BeCa, BeSr, GeCd, GeBe, and GeMg, is conducted. Using the full‐potential linearized augmented plane wave approach within the density functional theory framework, this analysis confirms the materials’ structural and dynamic stabilities through negative formation energies and adherence to elastic constant stability criteria. The generalized gradient approximation and the modified Becke–Johnson (mBJ) potential for electronic structure calculations are utilized. Notably, Cs2B′B″I6 DPs with B′B″ as BeCa or BeSr exhibit direct bandgaps (Γ–Γ), while those with B′B″ as GeCd, GeBe, or GeMg display indirect bandgaps (X–L). These findings offer valuable insights into the potential use of these materials in photovoltaic and optoelectronic devices. Furthermore, the exploration of thermoelectric properties, covering electrical conductivity, Seebeck coefficient, electronic thermal conductivity, and figure of merit at temperatures of 300, 600, and 900 K, suggests that Cs2B′B″I6 DPs, regardless of the specific B′B″ composition (BeCa, BeSr, GeCd, GeBe, GeMg), holds promise for applications in thermoelectric devices.