Study on the Morphology Evolution and Purification of Electrorefined Silicon

A three-layer process and apparatus have been developed for electrorefining of silicon for solar cell application. The anode is solidified from a hypereutectic solution of copper and MG silicon. At the temperature of operation (1223 K (950 °C)), elements that have an electronegativity greater than that of silicon will remain at the anode ( e.g. , Cu, B, P, etc. ) and then the Cu-Si phase can be used under certain conditions as a filter for purifying silicon with an electrorefining process. According to the stable liquid electrode reactive surface, high current density is possible during electrorefining and such advantages obviously improve the rate of deposition, which is a key point to reach commercial development. Deposited silicon particles are found embedded in electrolyte. Furthermore, with increasing operation time and current density, recombination of silicon particles is revealed and yields silicon balls with a diameter of 2 cm. The analysis of the anode feed and refined silicon shows a remarkable reduction of B and P concentrations, from 12.7 to 2.4 ppmw and 98.6 to 4.3 ppmw, respectively. Besides, particular mention should be made of efficient removal of impurities such as Fe, Mn, and Ti, which are present in significant quantities in the anode feed.