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）因其成本效益高而广泛应用于光伏应用。多晶硅的光伏特性强烈依赖于其晶粒尺寸、晶体取向和缺陷的存在。近年来，为了获得低缺陷密度的多晶硅，人们发展了多种技术，如类单晶硅、枝晶铸造生长和高性能多晶硅技术。然而，仍然存在着巨大的和内部的挑战有关：控制形核，孪生发生，晶粒竞争，缺陷的产生和它们在生长过程中的演变。因此，需要进一步了解从熔体中晶体生长机制，以提高这些工艺的竞争力，并达到高效的大规模生产。我们实验研究了从纯硅熔体中定向生长的原位观察系统，特别是晶体/熔体界面的演变，以探讨多晶硅生长机制。此外，通过电子背散射衍射（EBSD）进行晶粒结构信息，例如晶粒取向和晶界类型。原位观察数据和凝固晶体的特征提供了关于晶粒结构和过程中出现的缺陷的补充信息。我们着重于生长晶体/熔体界面，晶界发展和孪生发生，旨在加深对硅晶体生长过程的基本认识。

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.