Study of defects and impurities in multicrystalline silicon grown from metallurgical silicon feedstock

Nowadays the photovoltaic (PV) market suffers the severe shortage of silicon. One possible solution is to produce SoG-Si via a direct metallurgical route, followed by a final casting step. The use of such lower quality materials in solar cell production depends on the possibility of improving the electrical quality during the cell processing and requires a deep understanding of the interaction between defects. The aim of this work is to study the electrical properties and the minority charge carrier recombination behaviour of extended defects in a mc-Si ingot grown from metallurgical Si produced directly by carbothermic reduction of very pure quartz and carbon. The combined application of photoluminescence, infrared spectroscopy, electron beam induced current technique and transmission electron microscopy succeeded in identifying oxygen precipitates, decorated grain boundaries and dislocations as the defects which limit the quality of the metallurgical mc-Si and, therefore, the efficiency of the related solar cells.