Influence of Hubbard U correction on the structural, electronic and optical properties of Kesterite Cu₂XSnS₄ (X= Zn, Fe)

The new materials like quaternary chalcogenides semiconductors is an approach towards environment-friendly photovoltaic materials due to their promising potential as thin film solar cell absorbers. This work investigates the density functional theory (DFT) and density functional theory plus Hubbard U (DFT + U) approach on the kesterite phase of sulfide-based chalcogenides, Cu2XSnS4, CXTS (X = Zn and Fe) materials. The inclusion of the potential correlation term, U, plays a vital role in aiding the understanding of the complex many-electron problem, which LDA and GGA from DFT might not adequately describe. It was found that, by applying Hubbard U terms on p and d orbital states, the value of electronic band gaps can be significantly fixed close to the experimental value (similar to 1.3 eV-1.5 eV). The parametrized dependence of the band gap was well explained. The investigation of optical properties associated with the thin film applications on imaginary parts of the dielectric function shows that both structures have greater absorption at the energy range of 0-5 eV. Moreover, the refractive index and optical absorption show good results for both kesterite CXTS in the most effective wavelength of light to absorb sunlight (visible spectrum), which could exhibit a better finding for a suitable candidate for cost-effective new thin film solar cell application.