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

CBET-0755030 Derby太阳能级晶体硅是通过各种技术生产的，这些技术通过热传输过程熔化并小心地重新固化硅。这些过程通常涉及一个有趣的权衡：生长硅单晶的方法很昂贵，但这种材料可以实现最高的电池效率。较低成本的生长方法通常产生多晶材料，这导致电池效率较低。一种以低得多的成本生长硅单晶的有前途的技术，被称为水平带生长（HRG）工艺，在70年代和80年代初提出，但被放弃，转而采用更容易开发的更传统的方法。晶体生长建模和理解方面的累积进展有利于重新考虑HRG方法生长太阳能电池晶体硅。如果这一过程被成功部署，它可以显着降低硅衬底的生产成本，通过显着提高生长速度，并通过避免与从硅锭切割晶片相关的昂贵的切口损失。此外，HRG方法有望生长最高效率的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生长方法生产的多晶硅。一个成功的HRG工艺将通过促进硅太阳能电池同时降低成本和提高效率来实现变革。这里提出的工作的前提是，水平带状生长方法的巨大潜力将不会实现，直到更根本的理解其机械工作，使新的进展，在工艺开发。理论，热毛细管模型将开发和应用过程中的实验，以评估的HRG过程的可行性，用于生产晶体硅的光伏应用。这些研究将允许耦合传热和界面过程（凝固和毛细作用）在这个晶体生长system.Intellectual优点的建议activityThis工作将开发和应用严格的理论模型，研究热传输过程和界面现象，控制硅晶体生产通过水平带状生长过程之间的非线性相互作用的基本调查。特别的智力价值将是理解这个系统的稳定性和动态。与垂直的、由马库斯定义的晶体生长过程固有的稳定性不同，HRG过程可能是不稳定的，它的成功操作可能依赖于对系统设计和控制的透彻理解。拟议活动产生的更广泛的影响这项工作将通过在多学科和工业相关项目中培训研究生来促进发现和理解。它将通过促进与工业界的合作来加强基础设施。这项工作将直接影响Ribbon Technology International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实验观察与本工作中进行的理论。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当前技术的变革。传播活动将包括一个涉及明尼苏达科学博物馆的面向公众的外联方案。该项目由化学，生物工程，环境和运输系统（CBET）部门的热传输过程（TTP）计划，土木，机械和制造创新（CMMI）部门的材料加工制造（MPM）计划以及工业创新伙伴关系（IIP）部门的学术联络（GOALI）计划的资助，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).