A study on the fabrication of polycrystalline Si wafer by direct casting for solar cell substrate

Si-wafers for solar cells were cast in a size of 50 · 46 · 0.5 mm3 by a direct casting method. A graphite mold coated by boron nitride (BN) powder was used in order to prevent the reaction between carbon and the molten silicon. Without any coating, the reaction of the Si melt to the graphite mold was very severe. In the case of BN coating, SiC was formed in the shape of tiny islands on the surface of the Si wafer by the reaction between the Si-melt and the carbon of the graphite mold at high temperature. The grain size was about 1 mm. The efficiency of the Si solar cell was about 0.5% under AM1.5 conditions. It was lower than that of a Si solar cell fabricated with a common single- (sc, 3.0%) and polycrystalline (pc, 1.0%) Si wafer, which showed much lower efficiency than that of other commercial pc- or sc-Si solar cell (10–15%). 2005 Elsevier Ltd. All rights reserved.