Atomic Layer Deposition of Zn(O, S) Buffer Layer on CIGS Solar Cell

Abstract

Deposition of Zn(O, S) thin film as the Cd-free buffer layer is an important topic in Copper Indium Gallium Diselenide (CIGS) solar cells since it offers the potential enhancements for low cost and good for our environment. For CIGS buffer layer deposition, chemical bath deposition is the most common method in use. However, the incompatibility with in-line vacuum-based production methods is an issue of concerned. In this study, the buffer layer of Zn(O, S) thin films were fabricated by atomic layer deposition (ALD) method with alternately depositing of ZnS and ZnO thin films, using diethyl Zinc((C2H5)2Zn, DEZ), dimethyl sulfide((CH3)2S, DMS), and H2O as the precursors. As the alternative layers were deposited, atomic layer deposition technique exhibits good step-coverage, uniformity and accurate control of layer thickness. By changing the cycle ratios (m/n) of ZnS and ZnO, the oxygen (O)/sulfide(S) composition can be controlled in the Zn(O, S) buffer layer thin film as shown in Fig. 1. Various O/S composition ratios of Zn(O, S) thin films were deposited on the CIGS absorber. The optical properties, microstructure and chemical analyses of the deposited Zn(O, S) buffer layer thin films were carried out by ellipsometry, scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The CIGS device performances were measured by current-voltage (I-V) measurements. Keywords: CIGS, Zn(O, S) buffer layer, atomic layer deposition (ALD) References [1] U. P. Singh, S. P. Patra. International Journal of Photoenergy, 2010, 311–330.[2] N. Naghavi, S. Spiering, M. Powalla, B. Cavana, D. Lincot. Progress in Photovoltaics: Research and Applications, 2003, 11, 437-443[3] U. Zimmermann, M. Ruth, M. Edoff. Proceedings of the 21st European Photovoltaic Solar Energy Conference, Dresden, 2006, 1831–1834.[4] A. Hultqvist, C. Platzer-Björkman, J. Pettersson, T.Törndahl, M. Edoff. Thin Solid Films, 2009, 517, 2305–2308.[5]J. Lindahl, J. T. Wätjen, A. Hultqvist, T. Ericson, M. Edoff and T. Törndahl. Progress in Photovoltaics: Research and Applications, 2013, 1588-1597. Figure 1