Cu content dependence of morphological, structural and optical properties for Cu2ZnGeS4 thin films synthesized by sulfurization of sputtered precursors

•CZGS films with different Cu contents were prepared by sputtering method.•Cu-rich films exhibit large grain size compared to those of Cu-poor films.•Square resistance decrease from 14.2 to 1.3 kΩ/□ with increasing grain size.•Band gaps of the films decrease from 1.97 eV to 1.80 eV as Cu content increases.•Reason for diverse values of Eg of CZGS based on the band theory is discussed.

Cu2ZnGeS4 thin films with different Cu contents were synthesized by sulfurization of radio-frequency magnetron sputtered precursors. Microstructural characterizations using scanning electron microscopy and X-ray diffraction reveal that all of the as-prepared Cu2ZnGeS4 thin films are well crystallized and present a visible increase of grain size with increasing Cu content. In this case, the corresponding square resistance of these films is found to decrease from 14.2 to 1.3 kΩ/□. Furthermore, ZnS phase can be observed in the Cu-poor sample determined by Raman spectroscopy. Band gaps of the films decrease from 1.97 eV to 1.80 eV with increasing of Cu/(Zn+Ge) ratio from 0.93 to 1.13. These results are helpful to further study on Cu2ZnGeS4 thin films that are applicable for manufacturing solar cell.