Amorphous and Microcrystalline Silicon Based Solar Cells and Modules on Textured Zinc Oxide Coated Glass Substrates
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Amorphous and Microcrystalline Silicon Based Solar Cells and Modules on Textured Zinc Oxide Coated Glass Substrates Bernd Rech, Joachim Müller, Tobias Repmann, Oliver Kluth, Tobias Roschek, Jürgen Hüpkes, Helmut Stiebig, Wolfgang Appenzeller Institute of Photovoltaics - IPV, Forschungszentrum Jülich GmbH, D-52425 Jülich, Germany ABSTRACT This paper addresses scientific and technological efforts to develop highly efficient silicon thin film solar modules on glass substrates. We present a comprehensive study of µc-Si:H p-i-n single junction and a-Si:H/µc-Si:H stacked solar cells prepared by plasma-enhanced chemical vapour deposition (PECVD) at 13.56 MHz excitation frequency. In the first step cell development was performed in a small area PECVD reactor showing the relationship between deposition process and resulting solar cell performance. Subsequent up-scaling to a substrate area of 30×30 cm2 confirmed the scalability to large area reactors. Moreover, we developed textured ZnO:Al films by sputtering and post deposition wet chemical etching as front contact TCO-material with excellent light scattering properties. A-Si:H/µc-Si:H tandem cells developed on this textured ZnO yielded stable efficiencies up to 11.2 % for a cell area of 1 cm2. First solar modules were prepared in our recently installed process technology, which includes PECVD, sputtering, texture etching and laser scribing on substrate sizes up to 30x30 cm2. Initial module efficiencies of 10.8 % and 10.1 % were achieved for aperture areas of 64 cm2 and 676 cm2, respectively. INTRODUCTION Silicon thin film modules based on a-Si:H and µc-Si:H tandem cells are one of the most promising future thin film PV technologies. Necessary prerequisites for a cost-effective mass production of solar cells incorporating µc-Si:H films are the demonstration of high deposition rates and scalability to large areas. Moreover, effective light trapping is essential to obtain high cell efficiencies at small absorber layer thickness. The a-Si:H/µc-Si:H tandem cell concept was pioneered at the University of Neuchâtel [1] using the VHF-PECVD technique. Since then several research groups have demonstrated high efficiencies by applying different deposition techniques, light trapping concepts and substrates [1-5]. First commercial solar modules were demonstrated by Kaneka Co. [5]. However, these modules are only available on the Japanese market so far. This contribution addresses scientific and technological efforts to develop highly efficient silicon thin film solar modules. The first part describes the development of textured zinc oxide films prepared by sputtering and post deposition etching as TCO material which provides excellent light trapping properties. The second part treats the development of microcrystalline silicon solar cells at high deposition rates using plasma enhanced chemical vapour deposition (PECVD) at 13.56 MHz plasma excitation frequency. Both techniques were developed on laboratory scale (substrate size: 10x10 cm2) and are now implemented in solar modules
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