Analysis of graded band gap solar cells with SCAPS

To simulate the complicated, graded structure of modern thin film CIGS solar cells, we followed a �material driven� approach. Each layer is considered as a compound A1-yBy; the desired composition grading y(x) over a layer is set; all materials properties are specified for the pure materials A and B; finally, the local materials properties are derived from the local composition. This strategy was implemented in our thin film solar cell simulation software SCAPS.The new facility was used to study CIGS based thin film solar cells with a graded absorber layer. We showed that a grading strategy with a Ga-poor bulk and narrow Ga-rich layers at both ends of the absorber can indeed lead to a more favourable trade-off between Jsc and Voc than can be obtained with uniform CIGS absorbers. However, this result depends on the specific assumptions on recombination