p-n junctions in (In,Se)/Cu(In,Ga)(Se,S)2 photovoltaic systems

The formation of the p-n junction in (In,Se)/Cu(In,Ga)(Se,S)2/SnO2 structures is studied. The space charge region can be shifted from the (In,Se)/CIGSeS interface to the CIGSeS/SnO2 interface by annealing at different temperatures. In this structure, SnO2 is a simple electrode. When the p-n junction is near SnO2, photovoltages up to 650 mV can be reached when lighting through SnO2. The formation of this p-n junction, in other words the formation of an n-type absorber layer, is related to copper and indium diffusions, resulting in an increase of VCu and InCu defect concentrations. We believe n-type conductivity of the junction is due to a high concentration of (2VCu+InCu) complex defects, which exists in the absorber layer driving the diffusion processes.