Admittance spectroscopy of cadmium free CIGS solar cells heterointerfaces

Cadmium free Cu(In,Ga)Se-2 (CIGS) solar cells, prepared with indium sulfide buffer layers In2S3 deposited by Atomic Layer Chemical Vapor Deposition, were investigated by admittance spectroscopy. The admittance spectroscopy performed on various solar cells, with different deposition conditions of the In2S3 buffer layer reveals two types of defects: a shallow level N-1 and a deeper one N-2. The same situation is also found generally in CdS/CIGS based solar cells. For this latter kind of solar cells, it has been well established that the N-2-type defect is located in the CIGS bulk whereas the spatial location of the N-1-type defect is not well defined. To address this issue we performed admittance spectroscopy on CIGS based solar cells with In2S3 buffer layer and we compared these results with those obtained from CIGS solar cells with US buffer layer. From the Meyer-Neldel behaviour observed on the pre-exponential factor of defect emission frequencies, we can well derive the capture cross-sections of the different defects on both kinds of devices coated with In2S3 or CdS. More precisely, it was found that for both kinds of devices, the N-1-type defect has the same capture cross-section regardless of the dispersion of its activation energy. As a result we can assume that this defect is most likely located in the CIGS absorber layer next to the heterointerface. (c) 2005 Elsevier B.V. All rights reserved.