Exploring photocatalytic, thermoelectric, and SLME efficiency of photovoltaic absorber layers for halide double antiperovskites K<sub>6</sub>NaAsX<sub>2</sub> (X = Cl, Br, I): a first-principles approach.

Abstract

Density functional theory (DFT) was used in this study to examine the structural, electronic, optical, mechanical, thermoelectric, photovoltaic, thermodynamic, and photocatalytic characteristics of double antiperovskite (DAP) compounds K₆NaAsX₂ (where X = Cl, Br, I). In order to optimise lattice parameters and obtain lower bandgaps, first-principles calculations were performed in WIEN2k using the FP-LAPW + LO method with Wu-Cohen GGA (WC-GGA) and the Tran-Blaha modified Becke-Johnson (TB-mBJ) potential. The bandgaps of 1.48 eV, 1.34 eV, and 1.16 eV were found for K₆NaAsCl₂, K₆NaAsBr₂, and K₆NaAsI₂, respectively, according to band structure investigations using TB-mBJ + SOC. The orbital contributions close to the Fermi level were revealed by the density of states. The optical characteristics, including reflectivity, absorption, extinction coefficient, and refractive index, were computed, while elastic stability creteria confirmed mechanical stability. Thermodynamic properties, including heat capacities, entropy, enthalpy, and Gibbs free energy, were also assessed. Spectroscopic limited maximum efficiency (SLME) analysis revealed promising solar cell efficiency, while photocatalytic results indicated strong oxidizing power suitable for water splitting. Overall, the reduced bandgaps and multifunctional behavior indicate these DAPs as promising candidates for eco-friendly optoelectronic and energy applications.