Admittance spectroscopy of cadmium free CIGS solar cells heterointerfaces

Abstract

Cadmium free Cu(In,Ga)Se 2 (CIGS) solar cells, prepared with indium sulfide buffer layers In 2S 3 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 In 2S 3 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 In 2S 3 buffer layer and we compared these results with those obtained from CIGS solar cells with CdS 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 In 2S 3 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.