First-Principles Insights into Structural, Electronic, Elastic, and Optical Behavior of AlGeX3 (X = Cl, Br) Perovskites

Halide perovskites have drawn considerable attention for their exceptional properties and the flexibility to fine-tune their composition. In this study, we use first-principles density functional theory (DFT) calculations with the WIEN2K code to investigate the structural, electronic, optical, and mechanical properties of cubic halide perovskites AlGeX3 (X = Cl, Br), exploring their potential for optoelectronic applications. Replacing Cl with Br alters the lattice parameters and unit cell volume, highlighting the role of halogen chemistry in shaping structural behavior. Electronic structure analysis confirms a direct bandgap, with values of 2.13 eV for AlGeCl3 and 1.96 eV for AlGeBr3, making them suitable for ultraviolet optoelectronics. Optical results reveal strong absorption, excellent electrical conductivity, and low reflectivity, making these materials promising for light-harvesting applications. Mechanical assessments, including bulk modulus (B), shear modulus (G), Young's modulus (E), anisotropic factor (A), Poisson's ratio, and Pugh's ratio (B/G), confirm that these materials maintain a stable balance between stiffness and ductility. Additionally, the Debye temperature (theta D) suggests strong thermal resilience, while formation energy calculations reinforce their thermodynamic stability. Overall, AlGeX3 (X = Cl, Br) emerges as a strong candidate for next-generation photodetectors and high-performance optoelectronic devices.