GOALI: Thermal-Capillary Analysis of the Horizontal Ribbon Growth of Solar Silicon via Finite-Element Process Models

CBET-0755030德比太阳能级结晶硅是通过各种技术生产的，这些技术通过热传输过程熔化和小心地重新凝固硅。这些过程通常涉及一个有趣的权衡：生长硅单晶的方法成本很高，但这种材料可以实现最高的电池效率。成本较低的生长方法通常会产生多晶体材料，导致电池效率较低。70年代的S和80年代初的S提出了一种以低得多的成本生长硅单晶的很有前途的技术，即水平带状生长工艺，但后来被抛弃，转而采用更传统的更容易开发的方法。在晶体生长模拟和理解方面的不断进步使得重新考虑用于太阳能电池的晶体生长的HRG方法是有利的。如果成功部署这一工艺，它可以显著提高生长速度，并避免与从硅锭切割晶片相关的代价高昂的开槽损失，从而显著降低硅衬底的生产成本。此外，HRG方法保证以最高效率生长太阳能电池所需的单晶材料，而不是目前通过铸造和垂直带状生长方法生产的多晶硅。成功的HRG工艺将促进硅太阳能电池的成本降低和效率提高，从而产生变革性的影响。这里提出的工作的前提是，只有对水平带状生长方法的机理有了更基本的了解，才能在工艺开发方面取得新的进展，才能实现水平带状生长方法的巨大潜力。将开发理论、热毛细模型并结合工艺实验应用，以评估HRG工艺用于生产用于光伏应用的晶硅的可行性。这些研究将为研究这种晶体生长系统中耦合的热传递和界面过程(凝固和毛细作用)提供基础。这项工作的智能优点这项工作将建立和应用严格的理论模型来研究热传输过程和界面现象之间的非线性相互作用，这些界面现象通过水平带状生长过程控制硅晶体的生长。了解这一系统的稳定性和动态性将是一项特别有学术价值的工作。与固有稳定的垂直、半月面定义的晶体生长过程不同，HRG过程可能是不稳定的，其成功运行可能依赖于对系统设计和控制的透彻理解。拟议活动产生的广泛影响这一努力将通过培训研究生从事多学科和工业相关的项目来促进发现和理解。它将通过促进与行业的合作来加强基础设施。这项工作将直接影响国际带状技术公司的工艺开发，该公司由水平带状生长(HRG)工艺的创始人Bleil创立。这种相互作用将利用本工作中进行的理论的实验观察。从更广泛的角度来看，成功的HRG工艺可以通过同时降低硅晶体生产成本和提高太阳能电池效率来引发对当前技术的变革性支持。传播活动将包括一个由明尼苏达州科学博物馆参与的面向普通公众的外联计划。该项目由化学、生物工程、环境和运输系统(CBET)分部的热传输工艺(TTP)计划、材料加工与制造(MPM)计划、土木、机械和制造创新(CMMI)分部以及工业创新与合作(IIP)分部的学术联系(GOALI)计划联合资助，所有这些都在工程局(ENG)内。

CBET-0755030Derby Solar-grade, crystalline silicon is produced by a variety of techniques which melt and carefully re-solidify silicon via thermal transport processes. These processes typically involve an interesting trade-off: Methods that grow single crystals of silicon are expensive, but such material achieves the highest cell efficiencies. Lower-cost growth methods typically produce multi-crystalline material that results in cells of lower efficiency. A promising technology to grow single crystals of silicon at much lower costs, known as the horizontal ribbon growth (HRG) process, was put forth in the 70's and early 80's but was abandoned in favor of more traditional methods that were easier to develop. Accumulated advances in crystal growth modeling and understanding make it propitious to reconsider the HRG method for growing crystalline silicon for solar cells. If this process were successfully deployed, it could significantly reduce production costs for silicon substrate by dramatically increasing growth rates and by avoiding the costly kerf losses associated with cutting wafers from silicon ingots. In addition, HRG methods promise the growth of single-crystal material needed for solar cells of the highest efficiency, rather than multi-crystalline silicon currently produced by casting and vertical ribbon growth methods. A successful HRG process would be transformative by promoting simultaneous cost reductions and efficiency increases for silicon solar cells. The premise of the work proposed here is that the great potential of the horizontal ribbon growth method will not be realized until a more fundamental understanding of its mechanistic workings enables new progress in process development. Theoretical, thermal-capillary models will be developed and applied in conjunction with process experiments to assess the feasibility of the HRG process for the production of crystalline silicon for photovoltaic applications. These studies will allow for fundamental investigations of coupled heat transfer and interfacial processes (solidification and capillarity) in this crystal growth system.Intellectual merit of the proposed activity This work will develop and apply rigorous theoretical models to study the nonlinear interactions between thermal transport processes and interfacial phenomena that control silicon crystal production via the horizontal ribbon growth process. Of particular intellectual merit will be understanding the stability and dynamics of this system. Unlike vertical, meniscus-defined crystal growth processes that are inherently stable, the HRG process may be unstable, and its successful operation will likely rely on a thorough understanding of system design and control.Broader impacts resulting from the proposed activity This effort will advance discovery and understanding by training a graduate student in a multi-disciplinary and industrially relevant project. It will enhance infrastructure by promoting collaborations with industry. This work will directly impact process development at Ribbon Technology International, a company founded by Bleil, the originator of the horizontal ribbon growth (HRG) process. This interaction will leverage experimental observation with the theory conducted in this work. From a broader perspective, a successful HRG process could trigger a transformative enabling of current technology by simultaneously reducing silicon crystal production costs while improving solar cell efficiency. Dissemination activities will include an outreach program for the general public involving the Science Museum of Minnesota. This project is jointly funded by the Thermal Transport Processes (TTP) Program, of the Chemical, Bioengineering, Environmental, and Transport Systems (CBET) Division, by the Materials Processing & Manufacturing (MPM) Program, of the Civil, Mechanical, and Manufacturing Innovation (CMMI) Division, and by the Grant Opportunities for Academic Liaison with Industry (GOALI) Program, of the Industrial Innovation & Partnerships (IIP) Division, all within the Directorate for Engineering (ENG).