Comprehensive DFT Study on the Structural, Electronic, Optical, Mechanical, and Thermodynamic Behavior of Lead-Free AZnX3 (A = Al, Ag; X = Cl, Br) Perovskites for Optoelectronic Applications

Abstract

This study offers an in-depth examination of the physical characteristics of cubic AZnX3 (A = Al, Ag; X = Cl, Br) halide perovskites, conducted through ab initio Density Functional Theory (DFT) calculations. The research indicates that substituting Al with Ag at position A and Cl with Br at position X results in a reduction of the compound's structural stability. The AlZnBr3 compound demonstrates the greatest lattice parameter and primitive cell volume, whereas AlZnCl3 presents the smallest values for both parameters. The evaluation of formation energy and Born stability criteria confirmed the compounds’ chemical and mechanical stability. The indirect band gaps for AlZnCl3, AlZnBr3, AgZnCl3, and AgZnBr3 were determined by the GGA-PBE functional to be 0.939 eV, 0.290 eV, 1.423 eV, and 0.111 eV, respectively. The adjusted band gaps using Meta-GGA are 1.433 eV, 0.781 eV, 1.966 eV, and 0.669 eV for the respective compounds. A comprehensive evaluation of the density of states further confirmed the semiconducting characteristics. A thorough analysis was conducted of the perovskites’ optical properties, which included the dielectric function, absorption coefficient, optical conductivity, reflectivity, refractive index, and extinction coefficient. The properties of the compounds, including their elastic constants, mechanical characteristics, and anisotropic behavior, were thoroughly investigated. AlZnCl3 exhibits exceptional flexibility, workability, and strength. The distinct characteristics of all compounds are illustrated using three-dimensional contour maps. The thermodynamic analysis further validated the ability of these materials to sustain stability across varying temperature ranges. In summary, the results indicate that AZnX3 perovskite compounds represent the best option for high-performance multijunction solar cells and optoelectronic devices.