Impact of halogens modifications on physical characteristics of lead-free hybrid double perovskites compounds Cs2YCuX6 (X=Cl, Br, and I) for energy storage applications: First principles investigations

The purpose of this study is to examine the structural, electronic, optical, and thermoelectric features of novel double perovskite Cs₂YCuX₆ (X=Cl, Br, and I) for the first time in order to look for potential applications in solar power systems. Using first-principles calculations based on the widely recognized Density Functional Theory (DFT) and the PBE-Generalized Gradient Approximation (GGA) functional included in the WEIN2k package, the characteristics of the perovskites were determined. From the results of band structure and Total Density of States (TDOS) the energy band gap of Cs₂YCuCl₆, Cs₂YCuBr₆, and Cs₂YCuI₆ are observed 2.34 eV, 2.03 eV and 1.68 eV respectively. The PDOS outcomes shows that the formation of the valance and conduction bands is due to the hybridization of Cu-3d and halogen ions such that (X=Cl, Br, and I). The calculated values of goldsmith’s tolerance factor and formation energy reveal that the examined halide perovskites are structurally and thermodynamically stable. The electron localization function ELF and bader charge analysis show that the ionic nature between Cs and halogen ions X. Regarding the optical behavior, Cs₂YCuI₆has shown maximum absorption of electromagnetic radiation and conductivity in the ultraviolet and visible region i.e. (128–471 nm) which makes it a suitable candidate for optoelectronic and solar cell applications. The thermoelectric properties of the studied compounds have been calculated by means of the Boltztrap code. The presented findings unveil that amongst all studied compoundsCs₂YCuI₆ is best candidate for solar cell and thermoelectric applications due to higher conductivity, larger absorption range, significant Seebeck coefficient and higher Power factor.