DEFECTS IN CU(IN, GA) SE-2 SEMICONDUCTORS AND THEIR ROLE IN THE DEVICE PERFORMANCE OF THIN-FILM SOLAR-CELLS

This contribution is a summary of an international, interdisciplinary workshop dedicated to defects in chalcopyrite semiconductors and their relation to the device characteristics of thin-film solar cells, held on 3-5 June 1996 in Oberstdorf, Germany. Results of different charact erization methods were brought together to identify common observation s. The comparison of results from electrical defect spectroscopy and l uminescence investigations confirmed the presence of energetic distrib utions of defects throughout the bandgap of chalcopyrite thin films. E lectrical defect spectroscopy detects a defect about 280 meV above the valence band edge of Cu(In, Ga)Se-2 regardless of the preparation con ditions of the sample. In a solar cell the density of this defect depe nds on the operation conditions. This observation might be related to the migration of copper in an electric field, which occurs even at roo m temperature. Other defects appear to be related to processing or imp urities. Photoluminescence decay measurements yield time constants of several nanoseconds under low injection conditions. Modelling of the c urrent-voltage characteristics of Cu(In, Ga)Se-2-based thin-film cells suggests that compensating acceptor states in the CdS or at the heter ointerface are responsible for the frequently observed cross-overs bet ween the dark and illuminated curves. (C) 1997 by John Wiley & Sons, L td.