Detection of trace impurities in Cu(In, Ga)Se2 thin film solar cells by laser ablation ICP-MS

CIGS solar cells (CIGS: CuInSe₂, doped with gallium) on flexible glass fibre substrates were investigated to determine a possible migration of compounds from the substrate through the back contact layer into the absorber layer. We employed laser ablation ICP-MS to perform depth profile analysis as this technique combines ease of sample preparation with high sensitivity and moderate depth resolution. Careful optimization of the fluence and repetition rate of the laser system was necessary to ensure sufficient depth resolution in order to be able to relate the transient signals to the different layers. The results show that apart from sodium and small amounts of titanium no elements have migrated into the absorber layer. This was confirmed by micro-PIXE measurements on cross sections of the cell.