Electrical properties of the heterojunction in Cu(In,Ga)Se2 superstrate solar cells

The electrical properties of heterojunctions between wide gap n-type oxides and the p-type semiconductor Cu(In,Ga)Se-2 have been studied. The investigated oxides were a bilayer of undoped and aluminium doped ZnO, and the commercially available transparent conducting oxides SnO2:F (FTO) and In2O3-SnO2 (ITO). The junction of CIGS with ZnO showed the characteristic of a pn-junction, the temperature dependence of the current-voltage characteristics suggests interface recombination as dominating transport mechanism. This junction is suitable for photovoltaic light conversion and for the development of solar cells in superstrate configuration. The junctions of CIGS with FTO and with ITO showed poor rectifying behaviour and little or no response to illumination. The quasi-ohmic behaviour of these junctions was successfully used to replace the Molybdenum back contact with a transparent back contact in Cu(In,Ga)Se-2 substrate solar cells.