Uniform reference structures to assess the benefit of grading in thin film solar cell structures

The Cu(In,Ga)(S,Se)2-material system (CIGSSe) has an adjustable band gap which allows to make structures with a varying band gap throughout the film thickness. Because the performance of solar cells with a uniform composition is dependent on the band gap, it is necessary to compare the efficiency of a solar cell having such a graded band gap absorber with the efficiency of an adequate uniform reference sample. Several references are compared and a new procedure to assess the efficiency gain of graded band gap solar cells is introduced which allows a non-arbitrary and objective appraisal