A model for the open circuit voltage relaxation in Cu(In,Ga)Se-2 heterojunction solar cells

This article investigates the electronic transport properties of ZnO/CdS/Cu (In,Ga)Se-2 heterojunction solar cells during and after illumination or for ward bias in the dark. We observe a relaxation of the open circuit voltage under constant illumination as well as a relaxation current in the dark. Bo th phenomena are accompanied by an increase of the sample capacitance. We i ntroduce a general quantitative model concept for the open circuit voltage relaxation and related effects in heterojunction devices that explains the phenomena as a consequence of the persistent capture of charge carriers wit hin the space charge region. We apply our concept to develop a specific qua ntitative model for the observed metastablity in Cu(In,Ga)Sea heterojunctio n solar cells.