Charge carrier collection of chalcopyrite solar cells at grain boundaries and buried junctions

摘要

The charge collection of Cu(In,Ga)Se{sub}2 solar cells has been sensed by electron beam induced current (EBIC) and photo response measurements. A comparison between cells with and without CdS buffer layer was made. It is found that the charge collection function as derived by EBIC is not influenced by the buffer layer. No buried junction can be discerned in this case. For Cu(In,Ga)Se{sub}2 samples where Zn has been diffused from a ZnSe layer at 280°C, indeed a buried junction is observed. The buried junction is characterized by a reduced collection function near the interface. In the paper also the role of grain boundaries on the charge collection is studied. EBIC images where used to depict charge collection in the vicinity of grain boundaries. Using back side irradiation of Cu(In,Ga)Se{sub}2 solar cells, no grain boundary contrast is detected. The EBIC response is homogenous on the micrometer scale. This emphasizes that grain boundaries are not effective recombination sites in chalcopyrite semiconductor films. On the other hand the result points out the misleading interpretation of front surface EBIC showing bright EBIC contrast at grain boundaries.