Solar Cells Fabricated in Upgraded Metallurgical Silicon, Obtained Through Vacuum Degassing and Czochralski Growth

Abstract

Upgraded metallurgical grade silicon (UMG-Si) was obtained through metallurgical methods using two steps. First, metallurgical grade silicon was purified by the vacuum degassing technique using an electron-beam system. An ingot was then produced through Czochralski (CZ) growth. This later process was also used to reduce impurities through the segregation phenomenon in the CZ technique, producing a material of 99.9993% purity, one order of magnitude less pure than the minimum required for solar grade silicon. Solar cells fabricated with polycrystalline silicon with that amount of impurities are of low efficiency. Thus, the CZ technique was also adopted to supply monocrystalline silicon in order to avoid additional defects due to the grain boundary of polycrystalline wafers. Adopting this procedure, we produced solar cells with an efficiency of 13%, using a very simple fabrication process.