Previous work on CdS–CuInSe2 (CIS) solar cells, which reported distortions of their current-voltage (J–V) curves under red illumination, is expanded in this work to include CdS–CuIn1−xGaxSe2 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.

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A method is proposed and tested which allows for the accurate determination of the carrier collection efficiency and minority carrier diffusion length in Cu(In,Ga)Se2 solar cells using energy dependent electron beam induced current. Gallium composition gradients across the film thickness introduce quasielectric fields that are found to improve collection efficiency when they are located toward the rear of the sample. The quasielectric fields are also shown to reduce the influence of back surface recombination. The strengths and limitations of this technique are discussed and compared with external quantum efficiency measurements.