Electrodeposition of CIGS on Metal Substrates
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Electrodeposition of CIGS on Metal Substrates A. Kampmann, J. Rechid, A. Raitzig, S. Wulff, M. Mihhailova, R. Thyen and K. Kalberlah CIS Solartechnik GmbH, c/o Norddeutsche Affinerie, Hovestr. 50, D-20539 Hamburg, Germany ABSTRACT The development of a low cost roll-to-roll production process for CIGS remains an attractive goal. In the present approach, the absorber is prepared by electrodeposition techniques, while molybdenum, copper or stainless steel (SS) are used as flexible substrates. Two electrodeposition routes are evaluated: sequential plating of Cu, In and Ga followed by Se evaporation is compared to simultaneous (= ternary) electrodeposition of Cu, In and Se. Ternary electrodeposition yields 7.5 % efficiency on stainless steel. The sequential process leads to 9.0 % cell efficiency on copper and on stainless steel substrates. INTRODUCTION There is considerable interest in the development of a low cost production process for CIGS thin film solar cells, which are well suited for building integrated photovoltaics (BIPV). Following this idea we applied electrodeposition for absorber preparation and used flexible metallic substrates to be able to establish a roll-to-roll production process and to open new fields of applications like BIPV. Cell efficiencies between 10 and 13 % have been obtained using stainless steel substrates [1-5]. Contreras even reported an efficiency of 17.7 % without diffusion barrier between stainless steel and Mo back contact [6]. Investigations on copper substrates have not been published. Almost all authors use conventional vacuum based methods for absorber preparation. Electrodeposition of CIGS without additional vacuum deposition steps has lead to maximum efficiencies between 8.0 % and 8.8 % on molybdenum coated glass substrates [7,8] on small cell areas of 0.07 and 0.06 cm2 respectively. To our knowledge electrodeposition on metal foils has not been investigated so far. In this contribution results of a feasibility study are presented, which prove that electrodeposition on copper or stainless steel yields cell efficiencies reaching 9.0 % and 8.7 % respectively on 1 cm2 cell area. EXPERIMENTAL DETAILS Electrodeposition is carried out on rotating disc electrodes with a plating area of about 55 cm2. Two plating routes are investigated: simultaneous or ternary deposition of Cu, In and Se and successive or sequential plating of Cu, In and Ga followed by evaporation of Se. The resulting absorber thickness is 2200 nm for ternary absorber and 1300 nm for the sequential absorber. The deposited precursor films are heat-treated in a rapid thermal process (RTP) furnace. Temperature ramps up to 40°C/s are possible using radiation heat from halogen lamps positioned around the sample. Annealing is performed under nitrogen gas atmosphere at 1 bar. The cells are completed by conventional CBD-CdS and ZnO processes. J-V-curves are recorded under AM 1.5 sun simulation without grid on 0.25 cm2 or 1 cm2 area. In case of 1 cm2 cells four current contacts are used.
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