Computational insights into structural, elastic, optoelectronic, and thermodynamic properties of silver-based germanium ternary halide perovskites

This study explores the characteristics of AgGeX₃ (X = Cl and F) using density functional theory (DFT), examining their structural, electronical, optical, elastic, thermal properties, and phonon modes. Both compounds have a perovskite-like crystal structure, with AgGeCl₃ having a wider lattice constant (5.17 Å) than AgGeF₃ (4.36 Å). AgGeCl₃ has an indirect band gap of 0.553 eV, suitable for wide-range light absorption in optoelectronics, whereas AgGeF₃ possesses a larger band gap. AgGeF₃ exhibits a higher bulk modulus 53.26 GPa than AgGeCl₃ 28.91 GPa, implying greater resistance to deformation. Optical properties shows that AgGeCl₃ have high absorption coefficient, optical conductivity, refractivity, and reflectivity which make it suitable to absorb light in visible range while AgGeF₃ in UV range. By analyzing their thermal properties, AgGeF₃ shows higher heat absorption (157.7 J/mol·K) and resistance to temperature changes (480 K at 20 GPa), while expanding less (6 × 10⁻⁵ K⁻¹ at 0 GPa) and shrinking less under pressure. This makes it more stable under heat. In contrast, AgGeCl₃ expands more (24 × 10⁻⁵ K⁻¹ at 0 GPa) and resists temperature changes less (450 K at 20 GPa). These differences suggest AgGeF₃ is better for applications with high pressure and sensitive temperature requirements, while AgGeCl₃ is better for tasks like converting heat to electricity, creating electricity from light, and making electronics that can bend.