Horizontal Ribbon Growth of Single-Crystal Silicon

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The manufacture of high efficiency solar cells to convert solar energy to electrical energy currently makes use of a process known as the Czochralski growth process to fabricate high quality silicon wafers. A lower-cost, more efficient manufacturing approach for manufacturing these high quality single-crystal silicon wafers, called horizontal ribbon growth, has been developed. Compared to Czochralski growth, horizontal ribbon growth has the potential to produce thinner and larger wafers at a faster rate and a lower cost, with up to 75% potential cost savings. Commercialization of the horizontal ribbon growth process has been difficult, however, due to a lack of fundamental understanding of the physics that control this process. This award supports research that will contribute new knowledge related to a novel process for manufacturing single-crystal silicon wafers called horizontal ribbon growth. There are currently no models of the process that predict all of the phenomena observed in horizontal ribbon growth experiments. Most importantly, the maximum growth rates attainable have yet to be predicted. The goal of this work is to develop a model of the process that can predict the experimentally observed phenomena including the maximum growth rates. This model will then be used optimize the process so that it can be successfully commercialized. This has the potential to promote the development of new U.S. industries and to bring down the cost of solar energy to the point that solar energy would be cheaper than any other energy source. In addition, this research will contribute to work force training in the areas of fluid mechanics, thermal engineering, and materials science as well as broaden the participation of underrepresented groups in engineering research.There are currently no models that can accurately predict the horizontal ribbon growth process, and there are many experimental phenomena that occur that are unexplained. Developing a predictive model will give a greater understanding of the process, which will reduce the time and costs needed for commercialization. Because horizontal ribbon growth is not well-understood or studied, there is also an opportunity to make significant fundamental advances in our understanding of solidification kinetics. Studies at molecular to continuum scales will be used to understand and develop predictive models of the processes occurring. This understanding will then be applied to optimize the process and could also lead improvements in other crystal manufacturing processes.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.