Thin Single Crystal Silicon Solar Cells on Ceramic Substrates

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Crystal Solar been developing a technology for fabricating thin (< 50 micrometer) single crystal silicon wafers on foreign substrates. They reverse the conventional approach of depositing or forming silicon on foreign substrates by depositing or forming thick (200 to 400 micrometer) ceramic materials on high quality single crystal silicon films ~ 50 micrometer thick. Their key innovation is the fabrication of thin, refractory, and self-adhering 'handling layers or substrates' on thin epitaxial silicon films in-situ, from powder precursors obtained from low cost raw materials. This 'handling layer' has sufficient strength for device and module processing and fabrication. Successful production of full sized (125 mm X 125 mm) silicon on ceramic wafers with 50 micrometer thick single crystal silicon has been achieved and device process flow developed for solar cell fabrication. Impurity transfer from the ceramic to the silicon during the elevated temperature consolidation process has resulted in very low minority carrier lifetimes and resulting low cell efficiencies. Detailed analysis of minority carrier lifetime, metals analysis and device characterization have been completed. A full sized solar cell efficiency of 8% has been demonstrated.

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