Upgraded metallurgical silicon for application in the photovoltaic industry

The work is focused on the purification of metallurgical grade silicon into solar grade silicon. For the purpose of a cost effective production many well-known processes were theoretically and experimentally evaluated: reduction of silicon dioxide with carbon, reduction of boron with slag treatment, treatment with oxidative gas treatment (with a plasma torch and by gas flushing into the liquid silicon). Reduction of phosphorus was evaluated under vacuum in an induction furnace and with the electron beam technology. Reduction of other impurities we followed by controlled crystal growth and the segregation effect. Manufacturing of small quantities of silicon in an arc furnace using ultra-pure quartz and carbon in order to prove the producibility in principle were done. Most of the experiments have been carried out with commercially available metallurgical grade silicon produced for the aluminum industry. Material was manufactured by applying various technologies and using several experimental devices. From such material solar cells, showing 16 % efficiency, have been fabricated by an established cell manufacturer.