DFT-based study of Na₂AgAlX₆ (X = Cl, Br) halide double perovskites: insights from PBEsol, TB-mBJ, and HSE06 calculations for photovoltaic and photocatalytic applications

Abstract In this article, we investigated the Na 2 AgAlX 6 (X = Cl, Br) halide double perovskites for photovoltaic and optoelectronic applications. All calculations are performed using full potential linearized augmented plane wave method implemented in WIEN2k within the frame work of density functional theory. The structures of both the compounds were relaxed using GGA-PBE, and PBEsol functionals and optimized lattice constants of Na 2 AgAlCl 6 and Na 2 AgAlBr 6 were achieved using Birch-Muranghan equation of state. We calculated the values of tolerance factor, octahedral factor, formation energy and performed ab-initio molecular dynamic simulations to confirm the stability of the given perovskites. Electronic band structures and optical properties were calculated by employing PBEsol, TB-mBJ, and HES06 approximations, which disclosed that Na 2 AgAlX 6 (X = Cl, Br) compounds are semiconductors with band gaps of 1.49/1.76/216 eV and 0.78/.0.94/1.12 eV, respectively. Our results from elastic calculations revealed that the studied compounds are ductile, stable, and anisotropic, exhibiting flexible structures. We also investigated the photocatalytic properties of Na 2 AgAlX 6 (X= Cl, Br). The results showed that both compounds have potential applications in hydrogen production. The strong absorption spectra in both the visible and ultraviolet regions, along with smaller effective masses, exciton binding energies, and device absorption efficiency (∼90 for Na 2 AgAlCl 6 ), highlight the potential applications of Na 2 AgAlX 6 (X = Cl, Br) compounds in solar cells and optoelectronic devices.