Impurity control of quartz crucible coatings for directional solidification of silicon

Due to the price pressure for silicon photovoltaics the loss of silicon material during directional solidification has to be minimized. In the presented work the areas of reduced lifetime at the edges of a multicrystalline silicon ingot are investigated. Until now these areas cannot be used for solar cells. It has been studied which process parts in crystallizing silicon have an influence on this area. It was found that by reducing the impurity levels of the crucible material the area of low lifetime at the edge of the ingot is smaller. It was shown that the coating application has not a detrimental effect on the impurity level of the coating. The crystallization velocity also has an inferior role. Overall it can be said that a control of the impurity level of the crucible is crucial in order to reduce the low lifetime areas at the edge of the ingot.