Deep level transient spectroscopy measurements on Mo/Cu(In,Ga)Se2/metal structure

In thin-film Cu(In,Ga)Se2 (CIGS) solar cells a large number of intrinsic defect types are possible in the chalcopyrite structure and can influence the efficiency of the solar cell. Defect characterization is therefore essential. In this study Deep Level Transient Spectroscopy (DLTS) is used as an electrical defect characterization technique. The detection of defect related signals might be hindered by signals originating from barriers caused by the multi-layer structure and by a possible type inversion layer at the interface. To investigate to which extent the DLTS signals effectively arise from the CIGS absorber, solar cells are simplified to a metal/semiconductor/metal (M/S/M) structure. This was done by etching away the buffer and window layer and subsequent metal evaporation. In this way structures closer to those normally measured in DLTS are obtained. Additional etch processes targeted at thinning the absorber layer and/or removing oxidation layers are also performed. In general very similar DLTS signals are recorded for complete cells and M/S/M structures before and after additional etches.