One-dimensional simulation of sequentially processed Cu(In1−xGax)(Se1−ySy)2Cu(In1−xGax)(Se1−ySy)2 heterojunction solar cells with vertically graded absorber composition

The successful definition and verification of a one-dimensional device simulation baseline for sequentially processed Mo/Cu(In1−xGax)(Se1−ySy)2/CdS/i-ZnO/ZnO:AlMo/Cu(In1−xGax)(Se1−ySy)2/CdS/i-ZnO/ZnO:Al thin film solar cells is presented. The appropriate modeling of the layer sequence requires experimental assessment of the relevant material properties of each film within the layer sequence of the device. The properties of the CdS/i-ZnO/ZnO:Al window layer stack and of the molybdenum back electrode have been approximated by their bulk properties obtained from experiment and from the literature, respectively. This approach is, however, not meaningful for the sequentially processed Cu(In1−xGax)(Se1−ySy)2Cu(In1−xGax)(Se1−ySy)2 (CIGSSe) thin films due to characteristic segregation/grading of the chemical composition and the presence of structural inhomogeneities. This work shows that a suitable modeling of the CIGSSe film can be achieved by definition of effective medium properties. With this approach a 1D device simulation baseline for the studied system was established, which accurately reproduces the experimental characteristics of the studied CdS/CIGSSe heterojunction solar cells.