Incorporation of Na in Low-Temperature Deposition of CIGS Flexible Solar Cells

Abstract

AbstractDifferent methods for Na incorporation are known for the use of Na-free substrates like stainless steel or polyimide foil. In this work Cu(In,Ga)Se2 (CIGS) absorber layers with different amounts of Na are investigated. The CIGS samples were prepared via a roll-to-roll deposition process with ion beam assistance (Solarion) and by a multi-stage low temperature co-evaporation process (HZB). Na was either incorporated via in-situ co-evaporation of NaF (for roll-to-roll deposition) or by a Na-containing precursor (for multi-stage deposition). With increasing amounts of Na an increase of VOC is observed for both deposition tech-niques. In contrast, within the deposition parameters used, jSC decreases with increasing Na amount for co-evaporation of NaF while it seems unaffected when using a NaF precursor layer. The elemental depth profiles of the different CIGS thin films were studied via secondary ion mass spectroscopy and were found to depend strongly on the deposition technique. It seems that beneficial effects of the addition of Na are independent of the method of in-corporation, even if the distribution of Na in the CIGS layer is different due to different methods of incorporation and CIGS deposition processes.