Toward viable horizontal ribbon growth of solar silicon: Understanding and ameliorating process instabilities

可再生能源的发展可能是人类文明未来面临的最重要的挑战。低成本和可靠的太阳能到电力的转换方法对这一努力尤其重要。在这些方法中，迄今为止最成熟的技术是基于晶体硅制造太阳能电池。然而，这些技术所产生的每瓦成本需要大幅降低，才能使太阳能与化石燃料竞争。对于硅基太阳能电池，必须在保持或提高电池效率的同时降低生产成本。硅生长方法的进步需要实现这些目标。太阳级别的晶体硅是由多种技术生产的，这些技术通过加热过程将硅熔化并仔细地重新固化。生长单晶硅的方法，如Czochralski法，是昂贵的，但这种材料能达到最高的电池效率。低成本的生长方法，如铸造和垂直带状生长，已经开发出来，但它们的多晶材料导致电池效率较低。一种很有前途的晶体生长技术，被称为水平带状生长（HRG）工艺，于20世纪60年代末提出，随后在20世纪70年代末和80年代初在日本和美国得到了发展。在令人鼓舞的早期结果之后，实验进展和工艺开发工作停滞不前，这种技术在20世纪80年代中期被放弃，取而代之的是更容易开发的传统方法。然而，最近，人们对HRG方法重新产生了兴趣，因为如果成功，它有望实现显著降低生产成本和生长高质量单晶材料的双赢局面。然而，需要在理解和优化这种生长方法方面取得重大进展，才能使其成为硅太阳能电池的大规模生产工艺。这项研究的目的是使硅的水平带状生长可行，特别是通过解决与其独特的几何形状和操作相关的失效模式。具体而言，该项目将应用复杂的水平带状生长方法的计算模型来阐明和改善已知的过程不稳定性，并研究与增加生长速率相关的突出问题，以进一步降低生产成本。本研究将应用以计算为中心的方法来探索这些问题，并最终优化生长条件。因此，这项研究将解决晶体生长的基本科学问题，并明确目标，以改进具有重要技术应用的材料。

CBET 1336164DerbyThe development of renewable energy may be the most important challenge for the future of human civilization. Low-cost and reliable solar-to-electric conversion methods are especially important toward this endeavor. Of these methods, by far the most established technology is based on the fabrication of solar cells from crystalline silicon. However, significant reduction in the cost per watt produced by these technologies is needed to make solar energy competitive with fossil fuels. For silicon-based solar cells, production costs must be decreased while maintaining or improving cell efficiency. Advances in silicon growth methods are needed to achieve these objectives. Solar-grade, crystalline silicon is produced by a variety of techniques that melt and carefully re-solidify silicon via thermal processes. Methods that grow single crystals of silicon, such as the Czochralski process, are expensive, but such material achieves the highest cell efficiencies. Lower-cost growth methods, such as casting and vertical ribbon growth, have been developed, but their multi-crystalline material results in cells of lower efficiency. A promising crystal growth technology, known as the horizontal ribbon growth (HRG) process, was put forth in the late 1960's and was subsequently advanced in the late 1970's and early 1980's in Japan and in the U.S. After encouraging early results, experimental advances and process development efforts stalled, and this technique was abandoned by the mid-1980's in favor of more traditional methods that were easier to develop. Recently, however, there has been renewed interest in the HRG method, since, if successful, it promises a win-win scenario of significantly reduced production costs coupled with the ability to grow high-quality, single-crystal material. However, significant advances in the understanding and optimization of this growth method are needed to make it viable as a large-scale production process for silicon solar cells.This research is aimed at making the horizontal ribbon growth of silicon viable, particularly by addressing failure modes associated with its unique geometry and operation. Specifically, this project will apply sophisticated computational models of the horizontal ribbon growth method to elucidate and ameliorate known process instabilities and to study the salient issues associated with increasing growth rates to further reduce production costs. This research will apply a computation-centric approach to probe these issues and ultimately optimize growth conditions. Thus, this research will address fundamental scientific issues of crystal growth together with a clear goal toward improving a material with important technological applications.