Effect of light soaking on the electro- and photoluminescence of Cu(In,Ga)Se2 solar cells

ZnO/CdS/Cu(In,Ga)Se2 solar cells are investigated by spectrally resolved electroluminescence and electro-modulated photoluminescence. The results agree well with the reciprocity relation between luminescence emission and photovoltaic quantum efficiency. In contrast, the superposition of photoluminescence and electroluminescence emission is warranted only in a limited injection range. At higher injection levels, we observe a characteristic discrepancy between electroluminescence and electro-modulated photoluminescence which is reduced by light soaking. We attribute this anomaly to a potential barrier close to the CdS/Cu(In,Ga)Se2 interface. Hole injection into the space charge region during light soaking reduces this barrier and enhances the luminescence efficiency by a factor of 2.5.