LAUSR

The persistent photoconductivity (PPC), i.e., the metastable increase in hole concentration due to light soaking in Cu-poor Cu(In_0.7,Ga_0.3)Se₂ solar cells is observed to be proportional to the Na concentration in the absorber layer. Hole concentration in cells and conductivity in thin films follow a similar trend, suggesting that the effect originates from the absorber layer and is somehow linked to sodium concentration. Our results suggest that the large lattice relaxation model of an amphoteric V_Se–V_Cu vacancy complex being responsible for PPC cannot itself explain the Na-PPC relation. Therefore. either the passivation of the grain boundary barriers by sodium or a sodium-related modification of a defect complex needs to be included in the model.