Novel Lead-Free Perovskites FrZnX3 (X = F, Cl, and Br) for Optoelectronics Applications: A DFT Study

Abstract

This investigation examines the physical characteristics of the perovskite compounds FrZnX₃ (X = F, Cl, and Br) to develop lead-free cubic perovskite materials with robust optoelectronic capabilities, using density functional theory (DFT). The optimized cell structure fulfills all the stability criteria, with lattice parameters of 4.35, 5.12, and 5.41 Å for FrZnF₃, FrZnCl₃, and FrZnBr₃, respectively, using the generalized gradient approximation (GGA)-Perdew–Burke–Ernzerhof (PBE) functional. In contrast, hybrid HSE06 yields lattice parameters of 4.01, 4.76, and 5.01 Å, respectively. The findings indicate that the band gap diminishes with increasing halogen size for GGA-PBE and hybrid HSE06 functional, suggesting enhanced conductivity. FrZnF₃, FrZnCl₃, and FrZnBr₃ exhibit bandgap values of 3.241, 1.182, and 0.026 eV, respectively, for the GGA-PBE functional, indicating their excellent semiconductive characteristics. The bond between Fr and F is ionic and covalent for F and X, as shown in the electronic analysis. Poisson’s and Pugh’s ratios confirm the ductile nature. The examination of mechanical properties shows an inverse relationship between crystal size and stiffness. The anisotropic FrZnX₃ (X = F, Cl, and Br) compound also shows a diamagnetic nature. Excellent conductivity and absorption factor make this compound a promising alternative in energy-efficient coatings and transparent films. Additionally, reduced reflectivity in lower energy areas ensures a strong absorptive characteristic. The Hirshfeld charge decreases with increasing crystal size, as the distribution of charges within an atomic species also decreases. FrZnCl₃ exhibits increased sound velocities and Debye temperatures. FrZnBr₃ has an elevated level of specific heat and entropy. The calculated phonon dispersion of FrZnF₃ exhibits no imaginary frequencies, indicating its dynamic stability and suggesting that it can be synthesized experimentally.