Secondary barriers in CdS - CuIn 1 − x Ga x Se 2 solar cells

Previous work on CdS - CuInSe 2 ( CIS ) solar cells, which reported distortions of their current-voltage ( J - V ) curves under red illumination, is expanded in this work to include CdS - CuIn 1 − x Ga x Se 2 cells with variable Ga and CIS cells with variable CdS thickness. Different amounts of J - V distortion were observed in these cells under red light. The details are in good agreement with predictions of a photodiode model, in which a secondary barrier caused by the positive conduction-band discontinuity (spike) at the buffer-absorber interface is responsible for the current limitation. The illumination of the cell with high-energy photons lowers the barrier due to buffer photoconductivity, and thus removes the J - V distortion.