100 micron thick multicrystalline Si wafers and cells from large diameter EFG cylinders

Abstract

The reduction of silicon feedstock use is critical to the long-term success of the PV industry, due to needs for lowering cost, competition for the feedstock with the semiconductor industry, and for obtaining higher efficiencies via thinner substrates. Up to now, high productivity ribbon growth technologies, such as the edge-defined film-fed growth (EFG) octagon at ASE Americas, are limited to producing wafers with thicknesses of about 300 microns. We report here on a radical approach for producing thin wafers and solar cells. A 50 cm diameter EFG system has been constructed for production of hollow cylindrical tubes of multicrystalline silicon. We are currently investigating designs to increase the cylinder diameter to 1 m. The symmetry of this system allows for thinner growth: 75-100 micron thicknesses have been achieved. A Cu vapor laser has been used to cut 6 cm squares from the Si. Without optimization, 13.1% cells as thin as 150 microns have been achieved from this material.