Investigating the mechanism of silicon crystal growth from melt by in situ observation system

定向凝固生长的多晶硅(MC-Si)由于具有很高的性价比，在光伏领域得到了广泛的应用。MC-Si的光伏特性强烈依赖于其颗粒尺寸、晶体取向和缺陷的存在。近年来，为了获得低缺陷密度的MC-Si铸锭，人们发展了许多技术，如单晶硅、枝晶浇注生长和高性能MC-Si技术。然而，在控制形核、孪晶发生、晶粒竞争、缺陷产生及其在生长过程中的演化等方面，仍然存在着巨大的内部挑战。因此，为了提高这些工艺的竞争力和实现高效的大规模生产，需要进一步了解从熔体中生长晶体的机制。我们利用原位观察系统对纯硅从熔体中定向生长进行了实验研究，特别是对晶体/熔体界面的演化进行了研究，以研究多晶硅的生长机制。此外，还通过电子背散射衍射(EBSD)获得了晶粒取向和晶界类型等晶粒结构信息。原位观察数据和凝固晶体的特征提供了关于过程中出现的晶体结构和缺陷的补充信息。重点介绍了晶体/熔体界面的生长、晶界的发展和孪晶的发生，旨在加深对硅单晶生长过程中的基本认识。

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.