Theoretical study of GaBX₃ halide perovskites for optoelectronic and energy conversion applications

ABX₃ perovskite materials have shown great potential for optoelectronic applications in recent years. In this study, first-principles density functional theory (DFT) is used to thoroughly analyze the structural, electronic, thermo-mechanical and photocatalytic properties of lead-free novel cubic halide perovskites GaBX₃ (B = Cd, Zn; X = Cl, Br). Structural analysis brought about the thermodynamic stability in the space group Pm3̄m with negative formation enthalpy and decomposition energy. GaZnCl₃ was found to have the most stable material with a formation enthalpy of -2.938 eV per atom. Negative decomposition energies confirm the stability of these ternary phases against separation into binary constituents. Electronic band structure calculations, refined with the HSE06 functional, show that the bandgap of these novel materials varies from 0.65-3.37 eV. The optical properties are high absorption coefficients more than 10⁵ cm^-1 in the UV and visible regions, as well as a static refractive index between 1.85 and 2.20 increasing with Br substituent. The ductile nature (B/G > 1.75) and satisfying Born Stability Criteria proves mechanical stability. Thermal property analysis, including Debye temperatures up to 240 K, suggests high lattice rigidity and stability in Cl-based systems. Furthermore, the band edge alignments demonstrate that these materials possess the requisite redox potentials for visible light driven water splitting, with valence band maxima (VBM) and conduction band minima (CBM) effectively straddling the water oxidation and reduction potentials. While phonon dispersion curves at 0 K exhibit imaginary frequencies, indicating the cubic phase as a metastable state stabilized by finite-temperature effects. These findings strongly suggest the prospective applications of these novel materials in a wide range of optoelectronic devices.