Effect of halogen on the luminescence properties of two-dimensional double-perovskite (C6H16<mml:mi …

Two-dimensional (2D) metal halide perovskites have garnered significant attention in the field of light-emitting diodes due to their high photoluminescence quantum yield and tunability. In comparison with the widely studied 2D Ruddlesden-Popper (RP) perovskites, the 2D Dion-Jacobson (DJ) double perovskites, which offer higher stability and nontoxicity, have received relatively less attention. In addition, the regulatory effects of halogens on the luminescence mechanisms and performance of 2D DJ double perovskites remain unknown. Utilizing density functional theory, the stability and luminescence properties of 2D DJ double-perovskite (C₆H₁₆N₂)₂AgBiX₈·H₂O (X = Cl,0.2em0exBr,0.2em0exI) are effectively modulated through halogen substitution. The findings indicate that the dissociation energy incrementally increases as the halogen changes from I to Br to Cl, suggesting that the incorporation of lighter halogens enhances structural stability. The minimal self-trapping formation energy (i.e., 0.08 eV) of (C₆H₁₆N₂)₂AgBiI₈·H₂O facilitates easy detrapment of self-trapped excitons, leading to a tendency toward free exciton luminescence. The self-trapping formation energies of (C₆H₁₆N₂)₂AgBiBr₈·H₂O and (C₆H₁₆N₂)₂AgBiCl₈·H₂O are 0.77 eV and 0.96 eV, respectively, indicating substantial self-trapping depths; thus, favoring self-trapped exciton luminescence. In addition, the transition dipole moments of (C₆H₁₆N₂)₂AgBiBr₈·H₂O and (C₆H₁₆N₂)₂AgBiCl₈·H₂O are substantially higher than those of (C₆H₁₆N₂)₂AgBiI₈·H₂O, suggesting that substituting I with Cl and Br enhances the luminous efficiency of 2D DJ double-perovskite (C₆H₁₆N₂)₂AgBiX₈·H₂O (X = Cl,0.2em0exBr,0.2em0exI). These results indicate that halogen substitution can not only affect the stability of 2D DJ perovskites but also modulate their luminescent properties. Our research provides theoretical insights for the experimental design of superior luminescent materials.