新型电热冶金法制备太阳能级多晶硅的应用基础研究

Solar energy has become the most important energy in 21st century for solving the energy crisis, environmental pollution and global warming problems due to its unique advantages of inexhaustibility, clean and safety ect. There is an urgent need in our country to develop a technology of producing solar grade silicon (SoG-Si) with the low cost and energy consumption. Considering the key problems existing in the current metallurgical method to prepare solar grade multicrystalline silicon, based on the fact that the deep removal of boron and phosphorus from silicon is the most difficult process, we have put forward a short flow electrothermal metallurgical process with low cost to prepare solar grade multicrystalline silicon, which consists of purification of the raw materials, novel electrothermal metallurgical process, refining and directional solidifications. In the project, we focus on the most difficult removal elements in silicon, boron and phosphorus, and simultaneously give consideration to the representative metal impurities in silicon, iron and aluminum. The key project aims to investigate the behavior of such representative impurities as boron, phosphorus, iron and aluminum in the novel short flow process, to reveal the distribution and morphology of those impurities, to disclose the reaction mechanism and migration rules of those impurities in the acid leaching under ultrasonic field, microwave heating, and high vacuum and high temperature, which are applied to the raw materials, to clarify the reaction and removal mechanisms of those impurities in the novel alternating current (AC) or direct current (DC) electrothermal metallurgical systems, to understand the effect of the different purifier on the migration and removal of those impurities in the novel electrothermal metallurgical systems, to obtain the reaction and migration mechanisms of those impurities in molten silicon in the process of gas refining and liquid droplet refining. Finally, it is expected to fully understand the impurities removal mechanisms from silicon in the short flow electrothermal metallurgical process according to the results for the four representative impurities, to form the theoretical basis of the original short flow electrothermal metallurgical process to produce solar grade multicrystalline silicon, and provide theoretical guidance for the industrial production. The fulfillment of the project has important significance to the development of photovoltaic industry, breaking the international monopolies, solving environmental pollution and energy crisis in China.

针对我国对低成本低能耗太阳能多晶硅制备技术的迫切需求，针对我国目前冶金法制备多晶硅硼磷杂质难以去除的困境，申请人将冶金硅的制备技术应用于制备多晶硅，提出了流程短、成本低、原料易于提纯的新型电热冶金工艺：即原料提纯-新型电热冶金-精炼凝固-多晶硅。建议以难除的非金属杂质硼磷为研究重点和突破点、同时兼顾以铁铝为代表的金属杂质的去除，通过研究硼磷铁铝杂质在新型电热冶金过程中的行为：可揭示这些杂质在原料中的赋存状态及其在超声酸洗、微波加热和高温真空下的反应机理和迁移规律；阐明这些杂质在交流和直流的新型电热冶金体系中的反应机理及其在添加除杂剂下的迁移脱除机制；得到杂质在硅液中通气精炼和液滴化除杂的反应迁移机理。以期通过研究这四个杂质点来带动其他杂质去除的整个面，最终形成新型电热冶金法制备多晶硅的理论基础，为实践提供指导。项目的开展对我国发展光伏产业、打破国际垄断、解决环境和能源问题都有重要意义。

基于冶金法B、P难除的瓶颈，提出了“新型电热冶金法”制备多晶硅的思路。研究B、P、金属杂质在制备多晶硅整个体系中的反应和迁移机制。采用模拟和实验相结合、冷态和热态实验相结合、静态和动态实验结合，系统研究了“原料纯化、新型电热冶金过程、炉外精炼凝固”整个技术路线的热力学、动力学及科学问题，得到结论如下：.(1) 揭示了炼硅原料(石英砂、石油焦、木炭、碳化稻壳、晶体硅切割废料)中杂质B、P和Fe、Al杂质赋存状态；解析了当采用超声、微波等辅助外场后，原料中B、P等杂质在原料中的反应机制及迁移规律；建立了除杂动力学模型和除杂控制步骤，实现了炼硅原料的有效除杂。.(2) 阐明了在新型电热冶金体系中C-B/P、C-O-B/P和Si-C、Si-O、Si-C-O、Si-C-O-B/P体系反应热力学；研究了矿热炉内散料层、结壳层、反应层和产物层各层的反应过程、反应机理和质能传输过程；确定了B、P杂质在炉内各物料层的迁移规律。.(3) 研究了B、P、Fe、Al等杂质的赋存和分布；研究了CaO2-SiO2- CaCl2/CaF2、Na2O-SiO2、Li2O-SiO2等渣系对Si中B、P及金属杂质物相的演变、迁移和脱除机制；采用了合金溶剂法、真空精炼法、定向凝固法等研究了B、P杂质的物相转化、析出富集、扩散迁移、分凝行为和脱除机制。.(4)技术成果产业化1项： “新型电热冶金法制备高纯硅”实现产业化，由江苏浩博公司出资、东北大学提供全套技术创建了“内蒙古华鑫硅材料公司”。技术成果转让3项目：“炉外精炼深度去除B/P/Me杂质技术”成果在宁夏东梦科技公司进行转化；“炉外精炼除B、P技术硅靶材成分调控和异形硅靶材的制备”技术成果在宁夏高创特科公司进行转化；“新型电热冶金法制备太阳能多晶硅炉内精炼”技术成果在陕西中剑实业公司进行转化。.(5) 发表论文(2014~2018年)：发表论文60多篇，SCI收录34篇(JCR一区10篇，二区10篇，三区14篇。申报国家专利25余项，授权16项。参加国内外学术会议17次，出国交流5次。培养博士后2名，已经全部留校任教，毕业博士生6名(另4名在读)，毕业硕士16名(另9名在读)。