Molding and directional solidification of square ingots (5 cm × 5 cm × 8 cm height) and sheets (down to 1.3 mm thickness) of polycrystalline solar-grade Si have been performed in reusable molds by a new process involving the intercalation of a thin continous film of molten salt between the silicon and the graphite mold. The process relies on the capillary and wetting properties of the materials. The gravity forces exerted on the liquid Si are made negligible by the choice of a salt of nearly equal density. A graphite piston applied with a constant predetermined pressure forces the liquid Si into the corners of the mold and accommodates the volume increase on solidification. The extraction of the ingots from the crucible is easily performed either at room temperature with demountable molds or at high temperature by drawing the ingot out of the still molten salt. Solar cells with efficiencies comparable to the best commercial polycrystalline ones (8% without antireflective coating and before boron content optimization) have been made from this material. © 1987.
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