Evaluation of reactive sputtering of ZnS in Ar-O2 environment as a pathway to Zn(O, S) thin-films

Zn(O, S) has previously been demonstrated to be a viable replacement for the traditional CdS buffer layer in CIGS based thin-film photovoltaic devices. The deposition methods for Zn-based buffer layers include wet chemical bath deposition, PVD, ALD, and other techniques. This work focuses on the evaluation of Zn(O, S) layers on glass by sputtering. Results with RF reactive magnetron sputtering of a ZnS target in Ar-O₂ environment are demonstrated. Deposition rate decreases steadily with O₂ introduction without any sputter hysteresis; this suggests that the process is controllable. XRD confirms the presence of Zn(O, S), the composition of which can be tuned by varying S:O in the film. Initial results show 9.5% cell efficiency for CIGS devices with a Zn(O, S) buffer. QE suggests that the band-gap of Zn(O, S) buffer is higher than that of CdS buffer.