Computational exploration of the diverse functional properties of double antiperovskite materials Na6AgBiX2 (X = Cl, Br, I)

Abstract

The ongoing study investigates optoelectronic as well as photovoltaic characteristics of double antiperovskite (DAP) compounds Na₆AgBiX₂ (X = Cl, Br, I) using density functional theory (DFT) with semi-classical Boltzmann transport theory calculations, aiming at potential applications in renewable energy technologies. Optimizations of DAP Na₆AgBiX₂ (X = Cl, Br, I) show lattice constants (a) of ∼11 Å, which are increased from its counter double perovskite. The stability of these compounds was tested using formation energy (E_f), binding energy (E_b), Goldschmidt tolerance factor τ_G, elastically and thermodynamics. Electronic calculations reveal Na₆AgBiCl₂ and Na₆AgBiBr₂ possess direct bandgaps with energies of 1.27 eV and 1.22 eV, respectively, whereas Na₆AgBiI₂ displays an indirect band gap of 1.15 eV. The electron charge density reflects the balance of ionic and covalent interactions in these compounds. According to optical characteristics all substances exhibit considerable absorbing power in the visible region. Photocatalytic studies indicate that Na₆AgBiX₂ (X = Cl, Br, I) show a good response for oxidation. The calculated band-edge positions, evaluated using the electronegativity approach, indicate that the Na₆AgBiX₂ (X = Cl, Br, I) compounds are thermodynamically suitable for photocatalytic water splitting. The greatest value of ZT of 0.79 at 300 K among the compounds indicates that Na₆AgBiBr₂ may be a promising candidate for TE applications, according to its TE characteristics. In terms of solar cell efficiency predicted by SLME, Na₆AgBiBr₂ has a higher efficiency of 8.46% than Na₆AgBiCl₂ (@8.06%) and Na₆AgBiI₂ (@8.12%) for a 0.5 µm thick layer. All these findings underscore the potential of Na₆AgBiBr₂ for advanced renewable energy applications (such as optoelectronics, water splitting, thermoelectrics and photovoltaics).