Zinc-based buffer layer in the Cu(InGa)Se2 thin film solar cells

A ZnInxSey buffer layer and a ZnO buffer layer have been applied as an attractive alternative to the CdS buffer layer in the development of polycrystalline Cu(InGa)Se-2 (CIGS) thin-film solar cells and thus proposed the entire elimination of cadmium. For ZnInxSey/CIGS structure, we have already achieved 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 ZnInxSey/CIGS, we proposed a ZnO (low resistivity)/ZnO (high resistivity)/CIGS structure, where a high resistive ZnO layer was deposited by the atomic layer 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 DEZn flow rate was ranged between 40 and 53 mu mol/min, we obtained ALD growth 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 Omega cm) at these growth conditions. Up to now, we have achieved an efficiency of 13.2% (0.189 cm(2)) with a high resistive ZnO buffer layer. (C) 2000 Elsevier Science S.A. All rights reserved.