On the origin and formation of large defect clusters in multicrystalline silicon solar cells

Large defect clusters can represent a serious reduction of the material quality of multicrystalline silicon and the efficiency of the resulting solar cells. It is useful to find the origin of these defect-rich regions in order to understand their formations. For this work, multicrystalline silicon wafers from different positions of a compensated p-type silicon brick were processed to solar cells with a homogeneous emitter and screen-printed metallization. The solar cells from the main part of the brick showed efficiencies between 15.6% and 16.1%. The characterization for this work focuses on the positions of the three largest defect clusters by means of detailed optical, crystal orientation and electrical loss measurements. This allows the localization of the defect clusters' origins during crystallization. The locations where the observed defect clusters started to grow, show similar crystal configurations. This implies that the large clusters formed preferentially at grain boundaries between specific grain orientations. A smaller cluster disappeared at a grain boundary. The characterization showed the same crystal configuration as for the three large growing clusters.