Effect of segregation during crystallization of highly impure upgraded metallurgical silicon

One important aim of the photovoltaic industry is the continuous decrease of manufacturing costs of solar cells. For this reason, the use of upgraded metallurgical silicon (UMG-Si) instead of highly purified silicon or electronic grade silicon (EG-Si) is widely discussed. However, the direct application of this material for solar cells is difficult because of its higher amounts of dopants and metal impurities of up to several orders of magnitude in comparison to EGSi. Therefore, additional purification steps are necessary. In our approach we investigate the efficiency of segregation during crystallization of silicon feedstock with various purities from 99.99999% to 99.8%. Results of standard analysis methods like Atomic Absorption Spectroscopy (AAS), Inductively Coupled Plasma with Optical Emission Spectroscopy (ICP-OES) and Instrumental Neutron Activation Analysis (INAA) confirm the successful increase of the purity of the crystallized silicon up to a factor of 1000. Finally, solar cells produced from 99.999% pure silicon achieve an average efficiency near 15%.