Structural Aspects of Band Gap Grading in Cu(In,Ga)(S,Se)2-Based Solar Cells

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Structural analysis of multinary Cu(In,Ga)(S,Se)2 films demonstrates the feasibility of compositional grading in the depth of the absorber with respect to the S/(S+Se) ratio. Solar cells prepared from films with moderate S/Se gradients exhibit high open circuit voltages and efficiencies up to 13.9%. In this contribution we investigate strong S/Se gradients. Of particular interest are the thickness of a nearly homogeneous top layer as well as the impact of the crystallinity on the current voltage characteristics of solar cells. We show that the crystallinity of a homogeneous top layer strongly correlates with the performance of the corresponding devices.