Graded band gap CIGS solar cells considering the valence band widening

CIGS thin film solar cells with Valence Band (VB) and Conduction Band (CB) grading in the space charge region and back surface region of the absorber layer are proposed in this paper. In all the examined profiles the VB widening effects on the performance parameters by promoting the carrier transformation, hole passivation and carrier collection in the cell are considered. On the basis of the results, an optimal graded band gap structure is proposed and considered with a design closer to the reality where the VB offset is created during the band gap grading processes.