First results from a simplified Elkem Solar route-Input to tolerance limits

Elkem Solar has worked with a simplification of their metallurgical refining route for Solar Grade silicon.This involves removing the two last process steps, the directional solidification and post treatment, whilst the acid leaching is adapted to yield a product that can go directly to multicrystalline ingot. Results from the initial testing of the new product are presented. Multicrystalline ingots based on a 50% mix of the new product with virgin polysilicon have been made in a GT furnace and are compared to an ingot made from 100% virgin polysilicon in the same furnace. Solar cell results for three chosen brick positions (corner, edge and center) are presented and compared to the center position of the polysilicon reference. Both the brick yield (waferable amount of brick) and the cell efficiencies are comparable to the reference bricks and the new product is attaining maximum cell efficiencies of 17.3%. Additional cell parameters like shunt resistance, Reverse Breakdown Voltage (RBV) and Light Induced Degradation (LID) are well within acceptable level for standard module set-up. In parallel to the testing of the new product, lab-scale investigations of the tolerance limit in the feedstock for the elements aluminum and calcium have been conducted, and a tolerance limit for Al <0.5 ppmw is indicated. For calcium, addition of 40 ppmw to the silicon charge, showed no negative impact on the solar cell efficiency.