First-principles Investigation of Structural, Electronic, Mechanical, Optical, and Thermodynamic Properties of Lead-Free KSrX3 (X = F, Cl, and Br) Halide Perovskites for UV Optoelectronic Applications

This study employed density functional theory (DFT) within Quantum ESPRESSO to investigate the structural, electronic, phonon, mechanical, optical, and thermodynamic properties of cubic KSrX₃ (X = F, Cl, Br) halide perovskites for UV optoelectronic applications. All compounds were found to be structurally, thermodynamically, mechanically, and dynamically stable, as confirmed by negative formation energies, appropriate Goldschmidt tolerance factors, Born stability criteria, and phonon spectra without imaginary frequencies. KSrF₃ exhibited a direct band gap of 5.52 eV, while KSrCl₃ and KSrBr₃ showed indirect band gaps of 4.45 and 3.75 eV, respectively, making KSrF₃ the most promising candidate for deepUV applications. The compounds exhibited ductile behavior, characterized by dominant ionic bonding, low Debye temperatures indicative of low lattice thermal conductivity, and thermodynamic properties consistent with the third law of thermodynamics and Dulong–Petit’s law. Optical calculations revealed strong UV absorption and static dielectric constants of 2.02, 2.46, and 2.56 for KSrF₃, KSrCl₃, and KSrBr₃, respectively, highlighting their potential for UV optoelectronic devices.