Elemental depth profiling in Cu(In, Ga)Se2 solar cells using micro-PIXE on a bevelled section

Cu(In, Ga)Se2 (CIGS) solar cells deposited on polyimide foils by the Solarion company in a web-coater based process using sputter and evaporation techniques were investigated in the ion beam laboratory LIPSION of the University of Leipzig by means of Rutherford Backscattering Spectrometry (RBS) and Particle Induced X-ray Emission (PIXE) using a 2.25 MeV proton microbeam. From these measurements the composition of the absorber as well as the lateral homogeneity and the film thicknesses of the individual layers of the solar cell could be determined under some reasonable assumptions. Quantitative depth profiling of the individual elements was performed by micro-PIXE measurements on a bevelled section of a CIGS solar cell prepared by ion beam etching. It revealed small concentration-depth-gradients for Cu, In, Ga and Se within the CIGS absorber layer. Furthermore, a remarkable amount of Cd from the overlying CdS buffer layer was found to be present in the absorber layer. Secondary Neutral Mass Spectrometry (SNMS) measurements were applied on the same samples for comparison.