冶金法多晶硅生长界面行为及杂质分凝机制的外场调控

Interfacial mass transfer kinetic control and of solute segregation coefficient limit are the common problems of polycrystalline silicon during directional growth, Based on the morphology of growth interface and solute distribution during the process of crystal growth can be influenced by the magnetic field. The applicants proposed to control interface behavior and mechanism of impurities segregation with magnetic field technology during the process of crystal growth, which could solve the technical bottleneck of purity and quality stability for polycrystalline silicon prepared by metallurgical method, and promoting its large-scale application. In this project，the impurities segregation behavior was studied under different magnetic field conditions. To explore mechanism of impurity segregation for the solid-liquid interface shape change under the magnetic field. The interface shape of crystal growth was regulated by the magnetic field, improving the quality of polycrystalline silicon crystal growth. And the evolution law of interface morphology under different process conditions was obtained. By studying the relationship of the growth driving force between polycrystalline silicon growth rate, the kinetic theory of silicon crystal growth are established under magnetic field. It will provide an important theoretical and experimental basis for controlling directional growth of the multicrystalline silicon with magnetic field technology. This project will have very important positive significance for promoting industrialization process of multicrystalline silicon produced by metallurgical method, meanwhile it lays a solid foundation for sustainable development of photovoltaic industry of jiangxi province.

界面传质动力学控制和溶质分凝系数限制是晶体硅定向生长的共性问题，基于磁场可以影响晶体生长中熔体的界面形貌和溶质分布，申请者提出利用磁场技术控制冶金法多晶硅凝固过程生长界面行为及杂质分凝机制，突破冶金法多晶硅纯度指标和质量稳定性不理想的技术瓶颈，积极推动其规模化应用。本项目主要研究不同磁场工艺条件下杂质的分凝行为，探索磁场作用下固液界面形状改变对杂质分凝的作用机理；利用磁场调控晶体生长界面形状，改善多晶硅晶体的生长质量，并获得不同工艺条件下界面形态的演变规律；通过研究冶金法多晶硅生长速率与生长驱动力之间的关系，建立磁场作用下硅晶体生长的动力学理论，为利用磁场技术调控多晶硅定向生长提供理论和实验依据。本项目的研究对推进冶金法多晶硅产业化进程具有积极意义，同时为江西省光伏产业可持续发展奠定坚实的基础。

当前，超过90%的商业太阳能电池来源于硅材料。而冶金法多晶硅因低技术门槛、环境友好、成本较低等特点受到各国学者的关注。但由于其具有较多的晶体缺陷及高杂质含量而导致光电性能较差，难以实现大规模应用。基于磁场可以影响晶体生长中熔体的界面形貌和溶质分布，课题组利用磁场技术控制晶体生长，完成了未加磁场和施加磁场的不同条件下对晶体生长界面的影响研究，获得了坩埚厚度、线圈电流和磁场大小等工艺对多晶硅生长界面形态的影响规律；结合实验，研究了界面形态对多晶硅生长的影响机制，考察了不同凝固阶段硅熔体对流分布、方向和大小，及杂质元素的分布状态，明晰了外场调控下Fe等杂质元素的分凝行为；采用理论分析与实验相合的方法研究了不同磁场强度下硅锭不同区域的位错分布、孪晶结构和晶体取向，及低能孪晶的生长机理，获得了外场作用下凝固过程中杂质与固液界面的作用机理。这些研究为太阳能级多晶硅制备提供坚实的理论和工艺基础，对扩大冶金法多晶硅产业化及应用范围将具有十分重要的意义。