Directional solidification of silicon in carbon crucibles by an oscillating crucible technique

The quality of silicon cast by present techniques is limited by the presence of dislocations and grain boundaries in unseeded growth and by cellular structures with dislocation networks in the case of the seeded growth. To address these concerns, a new method of directional solidification called the oscillating crucible technique (OCT) is developed. During growth, a carbon crucible is oscillated to provide for effective stirring of the melt. This growth technique (seeded growth only), along with material characterization and solar-cell fabrication and testing, is described. Solar-cell efficiencies of up to 13 percent at 100 mW/sq cm area obtained in the single crystalline areas. Minority-carrier diffusion lengths exceeding 100 microns are measured even in the polycrystalline areas of the wafers. Limitations of the present setup and possible future improvements are discussed.