Zinc-based buffer layer in the Cu(InGa)Se-2 thin film solar cells

A ZnInxSey buffer layer and a ZnO buffer layer have been applied as an attr active alternative to the CdS buffer layer in the development of polycrysta lline Cu(InGa)Se-2 (CIGS) thin-film solar cells and thus proposed the entir e elimination of cadmium. For ZnInxSey/CIGS structure, we have already achi eved an efficiency of 15.1% (Y. Ohtake, T. Okamoto, A. Yamada, M. Konagai, K. Saito, Sol. Energy Mater. Sol. Cell, 49 (1997) 269). In addition to ZnIn xSey/CIGS, we proposed a ZnO (low resistivity)/ZnO (high resistivity)/CIGS structure, where a high resistive ZnO layer was deposited by the atomic lay er deposition (ALD) method. In ALD, we alternatively supplied source gases, DEZn and H2O. When the H2O flow rate was kept at 24.2 mu mol/min and the D EZn flow rate was ranged between 40 and 53 mu mol/min, we obtained ALD grow th of ZnO. The increase of growth rate was observed by the decrease of DEZn flow rate down to 15 mu mol/min and we obtained high resistive ZnO (1 K Om ega cm) at these growth conditions. Up to now, we have achieved an efficien cy of 13.2% (0.189 cm(2)) with a high resistive ZnO buffer layer. (C) 2000 Elsevier Science S.A. All rights reserved.