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Si Powder Based Substrates and Wafer Equivalent Based Solar Cells: Results of the European Project ThinSi
A. Ulyashin, M. Vardavoulias, S. Kamnis, R. Gløckner, B. Emamifard, S. Reber, J. Hampel, M. Drießen, J. van Hoeymissen, I. Kuzma-Filipek, M. Stange, M. Syvertsen, M. Cooke, C. Xu, K. Beekmann, G. Proudfoot, L. Bailey, K.-L. Choy, A. Sytchkova, D. Kozodaev, M. Tian, M.A. Vazquez
Light Trapping, Silicon (Si), Sputtering, Transparent Conducting Oxides (TCO), Silicon Solar Cell(s), Thin Film (TF), Substrate
Wafer-based Silicon Solar Cells and Materials Technology
Subtopic: Silicon Solar Cell Improvements
Event: 26th European Photovoltaic Solar Energy Conference and Exhibition
Session: 2CV.4.23
2202 - 2205
ISBN: 3-936338-27-2
Paper DOI: 10.4229/26thEUPVSEC2011-2CV.4.23
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Document(s): paper


ThinSi is a medium-scale focused research project founded by the European Commission, which aims to develop a solar cell processing chain for high throughput, cost-effective manufacturing of thin film silicon based solar cells on low-cost silicon supporting substrates. The substrates are made from the low-cost Si powder on the basis of innovative powder-to-substrate concepts using (i) spark plasma sintering, (ii) thermal spay, (iii) any other alternative method. Moreover, casting of a multi-Si ingot followed by sawing of wafers is used as a reference approach to prepare wafer equivalent based solar cells. Essential part of the ThinSi activity was concentrated so far on fabrication of Si powder with the desired purity, crystallinity and particle size. Experience from the partners using the Si powder for thermal spraying and tape casting followed by a spark plasma sintering (SPS), showed that a special refinement and adjustment of the Si powder quality was needed for each Si wafer sintering method, both with regard to conductivity and particle size distribution. It was established that a spark plasma sintering (SPS) of silicon powder with and without doping elements is a promising method to produce Si wafers with the desirable properties (dense structure and conductivity < 0.01 Ωcm) with diameters up to 200 mm2. Free standing ~300-500 μm thick 50x65 mm2 as well as 156x156 mm2 Si wafers have been produced from a low-cost and solar grade Si powders by the thermal spray method. These wafers exhibit all necessary properties (mechanical stability, ~0.01 Ωcm conductivity), Cost effective processes for the formation of a thin film silicon base on top of the low-cost supporting substrate based on: (i) high-temperature CVD, (ii) high temperature magnetron sputtering, (iii) thermal spray are under the development in this project. An advanced approach for the optical confinement based on incorporation of a porous Si Bragg reflector in the thin Si solar cell structure is applied for the solar cell processing. First solar cells on Si powder based substrates prepared via wafering of an ingot made of re-melted B-doped low purity silicon powder have been processed. The conversion efficiency for the best solar cell processed so far reached 11.9%.