DFT study of electronic and optical properties of Cu2ZnSiS4 chalcogenide compound and experimental investigation of improved PEC response of α-MoO3/Cu2ZnGeS4 nanocomposite

Abstract

The full potential linearized augmented plane wave method (FP-LAPW) is used to compute the optoelectronic properties of Cu2ZnSiS4 by employing the modified Becke-Johnson (mBJ) as the exchange correlation potential. The band structures, total and partial densities of states and optical properties including refractive indices are calculated. Moreover, we have fabricated the MoO3/Cu2ZnGeS4 nanocomposite and their structural, morphological, and photoelectrochemical performance is then experimentally investigated. According to the calculations, Si-p states contribute significantly to the formation of the conduction bands minima (CBM), whereas Cu-d states make up the valence bands maxima (VBM). A direct energy band gap exists in Cu2ZnSiS4 near the Brillouin Zone's centre (Γ-point) (BZ). We have observed the energy gap of 2.112 eV in mBJ which is significantly lower as compared to the experimental value of ∼3.07 eV. Using optical constants and electroreflectance plots, we have depicted the anisotropic behavior of Cu2ZnSiS4 and discovered that the ΔR/R in mBJ is 0.097 eV. The hydrothermal formation of Cu2ZnGeS4 compound with wide band gap photo catalyst (α-MoO3) as thin film photoelectrodes onto ITO substrates increased photocurrent density values by about 400 times when compared to pristine α-MoO3 photoelectrodes. The MoO3/Cu2ZnGeS4 nanocomposite exhibits greater photocurrent density values and better charge transfer because of their lower charge transfer resistance, enhanced charge carrier concentration, and decreased depletion layer width.