Electronic and optical properties of Cu2ZnGeX4 (X=S, Se and Te) quaternary semiconductors

•Study the electronic and optical properties of Cu2ZnGeS4, Cu2ZnGeSe4 and Cu2ZnGeTe4 using first-principles calculations.•Critical point structures in optical spectra are assigned to transitions based on the calculated band structures.•Trends in the variations of electronic band structure and optical properties are explored.•Good accord with the available experimental data is obtained. The electronic structures and optical properties of Cu2ZnGeS4, Cu2ZnGeSe4 and Cu2ZnGeTe4 in kesterite and stannite structures are investigated using first-principles calculations. The critical points in the optical spectra are assigned to the interband transitions according to the calculated band structures. The trends in the variation of the electronic and optical properties are discussed with respect to the crystal structure and the anion atomic number. Our calculated properties, such as, lattice constants, optical transitions, refractive index and dielectric constants are compared to the available experimental data and good agreement is obtained.