Multicrystalline silicon is widely used in solar cell production. The standard process applied by the industry is directional solidification in Si3N4-coated quartz crucibles, but little attention has been given to the coating and its impact on material quality. In this study, two 12 kg silicon ingots were directionally solidified. The first ingot had a better coating than the second ingot. The ingots were analyzed with respect to minority carrier lifetime, grain orientation, interstitial oxygen concentration and metal content as well as dislocation density. It was shown that the first ingot had considerably higher minority carrier lifetime, lower dislocation density and considerably larger grains than the second ingot. An explanation is put forward that this is due to the quality of the crucible coating and difference in the temperature at the point of nucleation of the crystal growth. In addition to the experiments, the influence of a Si3N4-coating layer on the thermal field during solidification has been investigated numerically. From these results it was concluded that the thickness of the coating layer has no influence on the solidification rate and the temperature field.
展开▼
