R.F. sputtering of high quality Cu/In precursor layers and conversion of CuInS2 using elemental sulfidisation processes

EPSRC funded project. Research on innovative routes to minimise environmental impacts of chalcopyrite PV absorber materials. Research offers low environmental impact conversion of absorber layers. Three, low toxicity, industrially applicable processes investigated (sulphidisation: 2- elemental, 1 patented anodic process). The paper was presented at a BACG conference, reviewed, then published in the Journal. Results relevant to future PV technologies. It represented a fruitful collaborative project with Cranfield University and an EPSRC funded fellowship. Projects were judged to be tending to outstanding by the reviewers (GR/N04645/01, GR/R10653/01). Thin films of CuInS2 have been produced by a two-stage process, the formation of a Cu/In precursor layer using r.f. magnetron sputtering of alternate layers of the elements followed by the conversion into the compound by either (i) annealing the precursor layers in a closed chamber in the presence of sulfur or (ii) annealing the precursor layers in sulfur that was transported over the layers using argon as a carrier gas. These out-of-line-ofsight methods have potential for large-scale batch processing of the absorber layers. The physical and chemical properties of the precursor layers and the CuInS2 formed were investigated using a range of methods including energy dispersive X-ray analysis, Rutherford backscattering spectrometry, and synchrotron X-ray diffraction. The data confirms that the uniform layers produced using the former method have potential for use in both substrate and superstrate configuration devices. For the latter method there was significant indium loss during the conversion process and this problem needs to be overcome before the layers can be used in solar-cell devices.