Electrical Properties of Subgrain Boundaries

Investigation of the electrical properties of sub-GBs is an important subject for improving the performance of Si multicrystal solar cells. In particular, the carrier recombination activity of sub-GBs has been well investigated 

To clarify the impact of sub-GBs on solar cell performance, in particular, the shunting effect, Kutsukake et al. performed EL imaging on a small solar cell sample, in which the distribution of sub-GBs was specified by using X-ray 

As reviewed above, sub-GBs are concluded to be most serious defects preventing the improvement of overall performance of solar cells based on Si multicrystals. We, therefore, suppress the generation of sub-GBs on the basis of fundamental knowledge of its mechanism. In the next section, the generation mechanism of sub-GBs is discussed. 

Sub-GBs are expected to be formed during a high-temperature growth process by the stabilization of dislocations, to form array-like configuration that minimizes the self-energy. To form dislocations, the existence of a source with a discontinuous crystal lattice is required, because extremely large stress, typically in the order of the modulus of transverse elasticity, is necessary to form a dislocation from a perfect crystal lattice. In the case of Si multicrystal growth, possible sources are the inner wall of the crucible, inclusions and GBs. 

In particular, regarding GBs, numerous observations and theoretical models of dislocation generation have been reported for metals and their 

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