Recombination centers in the Cu(In,Ga)Se2-based photovoltaic devices

Minority carrier traps in the absorber layer of the ZnO/CdS/Cu(In,Ga)Se-2 photovoltaic devices have been investigated by use of deep level transient spectroscopy. In the efficient baseline structures a recombination process involving deep electron trap is revealed in the presence of blue light introducing holes from the buffer into absorber. A large capture cross-section for minority carriers and high concentration exceeding net acceptor concentration suggest that this trap plays a significant role as a recombination center in these devices. Its specific features indicate that it might also be a center involved in the metastable phenomena characteristic for these devices. Another deep electron trap, observed in the cells of inferior performance, has been investigated by double pulse DLTS. We conclude, that its concentration and values of capture cross-sections for holes and electrons are too low to account for the low efficiency of these structures. (C) 2003 Elsevier Ltd. All rights reserved.