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1989
Conference Paper
Titel
Continuous processing of silicon sheet material by the SSP-method
Abstract
Purpose of the SSP project (Silicon Sheets from Powder) is to grow large area polycrystalline silicon sheets (100 x 100 square millimeters) for solar cells with high conversion efficiency (bigger than 13%). In a first step a thin layer of silicon powder is poured onto supporting plates made of quartz. In a second step the surface of this layer is melted by focussing light of halogen lamps onto the surface. The liquid silicon combines the powder particles. Thus a self-supporting pre-sheet is formed which can easily be removed from the quartz plates. In a third step this pre-sheet is converted into the final coarse-grained sheet by zone-melting also using focussed light as heat source. A new machine has been built up which allows continuous processing yielding ribbons. The freasibility of the technique was demonstrated by fabricating ribbons of up to 100 mm width and 500 mm length. The sheets are characterized by metallographical and electrical methods (e.g.EBIC). Test solar cells (20 x 20 square millimeters) demonstrated the quality of the SSP material. Conversion efficiencies ranged up to 13.2% (I sub sc = 29.8 mA/square centimeters, V sub oc = 563 m V,FF = 0.78). From I sub sc decay measurements local diffusion lengths of up to 250 mym were calculated.