Characterization of the CdS / Cu(In,Ga)Se2 interface by electron beam induced currents

The method of electron beam induced currents in junction configuration (JEBIC) has been employed to investigate carrier collection in Cu(In,Ga)Se₂ solar cells. A detailed analysis of JEBIC line-scans reveals unexpected carrier collection properties, which cannot be explained with common models. We ascribe this anomalous behavior to an electrostatic barrier effect at the Cu(In,Ga)Se₂ / CdS interface. We suggest the existence of a thin defect-layer on the surface of the Cu(In,Ga)Se₂ with high acceptor concentration and valence band edge that is energetically lower than that of the bulk. Using this model, we achieve a good agreement between experimental and simulated JEBIC line-scans. The influence of the barrier effect is considerably reduced by a metastable change of the interface properties induced by intensive electron irradiation of the interface. This effect is explained by a metastable decrease of the negative charge density in the defect-layer.