Analysis of the physical origin of trap centres and their effect on solar cells

Defect sites in silicon, which temporarily capture excess charge carriers (traps), are a promising source of information on defect structures relevant for PV-application of the material. In this work the correlation between traps in p-type silicon, structural crystal defects and impurities is explored in order to find the origin of these traps in multicrystalline silicon. The trap density is compared to the density of different impurities and structural crystal defects. These comparisons reveal that the trap density is positively correlated to the oxygen density and negatively correlated to the density of the metallic impurities analyzed. In addition we show that structural crystal defects are necessary but not sufficient for the existence of high trap densities. The properties of theses structural defects are further investigated by photoluminescence. In summary, structural crystal defects which are decorated by oxygen precipitates arise as likely origin of trap centers.