Fabrication of Cu₂ZnGeS₄ thin films by sulfurization of Cu₂GeS₃/ZnS stacked precursors

Abstract

The fabrication of Cu₂ZnGeS₄ (CZGS) was realized by depositing ZnS on a co-evaporated Cu₂GeS₃ film by RF sputtering, followed by sulfurizing. After sulfurization, CZGS thin films with Cu/Ge ratios of 2.1 and 1.6, and Zn/Ge ratios of 1.5 and 2.0 were obtained. The thin films obtained after sulfurization were assigned to tetragonal CZGS with ZnS segregation on the basis of X-ray diffraction and Raman measurements. The CZGS film with a Cu-poor and significantly Zn-rich composition showed a higher Voc and lower Jsc than did the CZGS film with a Cu-rich and Zn-rich composition. This suggests that good p-n junctions were formed in CZGS films with Cu-poor cells but the efficiency decreased because of the increase in series resistance due to ZnS segregation.