Model for electronic transport in Cu(In,Ga)Se-2 solar cells

Temperature-dependent measurements of the current-voltage characteristics a nd of the junction admittance of ZnO\CdS\Cu(In,Ga)Se-2 heterojunction solar cells are presented together with numerical modelling of these experimenta l results. We explain the cross-over between dark and illuminated current-v oltage characteristics currently observed for this type of device by the im pact of the defect chalcopyrite layer at the surface of the Cu(In,Ga)Se-2 a bsorber. Our model assumes an illumination-dependent voltage drop across a defect layer with a thickness of 15 nm to explain the cross-over, The volta ge drop results from the electrical dipole made up of donor-like states at the interface between the defect layer and CdS and deep Receptor states iir the defect layer itself The illumination dependence of this voltage drop i s explained by photogenerated holes trapped by the deep acceptor states in the defect layer. Numerical simulations have been carried out using the pro gram SCAPS-1D in order to verify our model assumptions. A om oar model, ind irect conclusions are derived concerning the maximum conduction band offset s between CdS and the defect layer and between CdS and ZnO, (C) 1998 John W iley & Sons, Ltd.