Method for ribbon solar cell fabrication

Abstract

A method and apparatus for casting material into a ribbon shape in which molten material to be cast is extruded in a thin ribbon onto a moving sheet of foil of a metal having a sufficiently lower melting point or which forms an alloy with the molten material which has a sufficiently lower melting point than the molten material, to cause almost immediate melting of at least a portion of the foil which comes in contact with the ribbon of molten casting material, with crystallization of the cast material occuring on a layer of liquified foil or foil-cast material alloy. Also disclosed is the disposing of the metal foil, in the vicinity of the contact with the ribbon of molten casting material, on a cooled surface which is moving past the region of extrusion of the molten material. The method and apparatus is disclosed to be particularly useful in making cast ribbon of semiconductor material with a foil backing and desirable properties for photovoltaic solar cell applications. In addition, it is disclosed to add dopant to the solidifying semiconductor material after extrusion onto the metal foil and/or to add dopant to the surface of the metal foil prior to contact with the molten material, and also to thermally control the rate of crystallization of the molten material.