Red-blue effect in Cu(In,Ga)Se2-based devices revisited

The controversial issue of a source for the fill factor losses in Cu(In,Ga)Se2-based solar cells observed under red light is discussed. Experimental evidence is presented that removal of the fill factor loss by blue light is accompanied by a decrease in capacitance. Similar kinetics for both effects are observed. This effect is demonstrated not only on CdS-buffered devices but also on Zn(O,S)- and In2S3-buffered cells. The explanation, supported by simulations, is based on a model of a reduction of the p + layer by holes photogenerated in the buffer. This effect might be differentiated from the effect of a photosensitive secondary barrier in the buffer-window part of the junction by a sign of the capacitance change under blue light.

► High-energy photons improve fill factor in Cu(In,Ga)Se2-based solar cells.
► The effect is demonstrated on three types of buffer layers.
► Fill factor improvement under blue light is correlated with a decrease of doping.
► p + layer is the main cause of fill factor deficiency under red light.