Krause, J.; Harbauer, K.; Welzel, T.; Ellmer, K.: Reactive co-sputtering of Cu(In,Ga)S2 absorber layers: role of Cu-excess and ion assistance. In: Ossenbrink, H. [u.a.] [Eds.] : 26th European Photovoltaic Solar Energy Conference 5 - 9 September, Hamburg, GermanyMünchen: WIP, 2011. - ISBN 3-936338-27-2, p. 3059-3063
Abstract:
: Reactive and non-reactive magnetron sputtering as a large-area, low-temperature, industrial deposition method is used already on a large scale in thin film photovoltaics, but only for electronically inactive films, i.e., back contacts (molybdenum, silver), front contacts (ITO, ZnO:Al) and metal precursor layers (copper, indium). Though we could show recently, that reactive magnetron sputtering of CuInS2 absorber layers by co-sputtering from a Cu and an In target yields cell efficiencies of more than 11 %, this process is not yet stable enough for module production, partly due to insufficient understanding of the growth process. In this article we investigate the crystallization process of Cu(In, Ga)S2 layers by in situ, time-resolved energy-dispersive X-ray diffraction (EDXDR) and study the influence of an additional plasma source on the film morphology and cell efficiencies. It is found that with increasing Cu excess the crystallization of Cu(In,Ga)S2 occurs at much lower temperatures (down to about 200 °C). This is comparable to the crystallization of evaporated CuInS2 with an CuSx top layer. An additional plasma directed to the substrate improves the efficiency of Cu(In,Ga)S2 cells considerably, if the plasma density is not too high. Too high plasma densities at the substrate lead to a re-sputtering of the growing films. From elemental SIMS profiles it is found, that the Ga profiles are flat, an advantage compared to the sequential process.