CONTINUOUS SOLIDIFICATION OF PHOTOVOLTAIC MULTICRYSTALLINE SILICON FROM AN INDUCTIVE COLD CRUCIBLE

An inductive cold crucible is used to melt photovoltaic granular silic on and to form massive multicrystalline billets by continuous pulling downwards. The cold crucible is noncontaminating. In the billet the im purity content is kept at the same low level as it is in the feed stoc k, even for copper, and somewhat lower for oxygen. Square billets are as easy to shape as circular ones. Continuous solidification gives the material uniform grain structure and properties, so that a considerab le reduction in waste material is expected. Details are given on the e xperimental procedure and on measurements. For a given pulling rate, t he optimal electrical conditions result from a fine compromise between the risk of a liquid leak, and the risk of nonmelting granules. Among the electrical and thermal measurements which were tested, the electr ical frequency seems to give a possible gage for estimating the variat ion of the amount of liquid. (C) 1998 Elsevier Science B.V. All rights reserved.