Characterization of graded CIGS solar cells

The CIGS material system has an adjustable bandgap. A ‘grading’ of the bandgap through the thickness of absorber can be used to improve cell performance. Some modern CIGS-solar cells already have a graded bandgap profile; for this work, such cells were provided by AVANCIS. We have set up a numerical model with the scaps program, based on a variety of cell measurements. This model then was applied to analyze the true benefit of bandgap grading. Grading appears to have only a limited effect on cell performance. Not only the effectively graded parameters, but also non graded parameters have an influence on the net benefit of grading.