Metastability in the electrical transport of Cu(In,Ga)Se2 solar cells

We report on a detailed investigation on relaxations of the open circuit voltage Voc of ZnO/CdS/Cu(In,Ga)Se₂ solar cells. Considering that persistent photoconductivity can be observed on Cu(In,Ga)Se₂ polycrystalline absorber layers as well as on Cu(In,Ga)Se₂ single crystals, we propose a model that describes the Voc relaxation as a property of the Cu(In,Ga)Se2 bulk material and not as a property of a specific interface of the heterojunction.