| 研究実績の概要 |
Multicrystalline silicon (mc-Si) grown by directional solidification is widely used in photovoltaic applications because it is very cost-effective. The photovoltaic properties of mc-Si are strongly dependent on its grain size, crystallographic orientation, and the presence of defects. In recent years, many techniques e.g. mono-like silicon, dendritic casting growth and high performance mc-Si techniques had been developed to get a mc-Si ingot with low defect density. However, there still exist large and internal challenges related to: the control of nucleation, twinning occurrence, grain competition, defect generation and their evolution during growth. As a consequence, further understanding of the crystal growth mechanism from melt is needed to increase the competitiveness of those processes and to reach an efficient mass production.
We experimentally study the directional growth of pure silicon from its melt using in situ observation system and particularly, on the evolution of crystal/melt interface to investigate multicrystalline silicon growth mechanism. Furthermore, the grain structure information e.g. the grain orientations and grain boundaries types was performed through electron backscattering diffraction (EBSD). The in situ observation data and the character of solidified crystal give complementary information on the grain structure and defects occurring during the process. We focus on the growing crystal/melt interface, grain boundary development and twinning occurrence, aiming at deepening the fundamental understanding during the silicon crystal growth.
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