Grain and solidification front control of multicrystalline silicon crystal growth for photovoltaic applications
Date Issued
2009
Date
2009
Author(s)
Yeh, Kuan-Ming
Abstract
We report simple ideas to control the grain orientation and solidification front to get high quality multi-crystalline silicon for solar cells. The method employed an active cooling spot to induce initial dendrite growth, and the solidification front was controlled to be slightly convex through crucible insulation. This active spot cooling employs a graphite rod at the bottom of crucible which served as an active cooling spot. According to silicon grain growth behavior, the undercooling caused by cooling spot at the initial crystal growth can induce grains with Σ3 grain boundary. The Σ3 grain boundary is electrically inactive so that it does not act as recombination center for solar cell. In addition, the cooling spot can control cooling rate to reduce new nucleation formation at the grain boundary during crystal growth. That is, it helps induced dendrite growth from the bottom to the whole crystal. As compared with non-controlled crystal, it was found that there were more twins and slip bands in controlled one. These areas often had high lifetime and low EPD density. Furthermore, grain size and lifetime of controlled crystal also enhance along the growth direction. As the results, the solar cell conversion efficiency is significantly improved.
Subjects
multicrystalline silicon
directional solidification
grain control
solar cell
SDGs
Type
thesis
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