Continuous Wafer Production for Solar Cells by Horizontal Ribbon Growth

[1438231]利用太阳能电池将太阳光直接转化为电能的技术还没有发展到可以在没有政府补贴的市场上产生重大影响的程度。太阳能电池的成本仍然很高，用于生产太阳能电池的技术也不容易扩大规模。按照目前的增长速度（每年20-30%），建造足够的太阳能发电厂和基础设施来取代化石能源需要几十年的时间。由于生产高纯度硅和单晶硅片的成本高昂，太阳能迄今尚未充分发挥其潜力。在流化床反应器中制备高纯度多晶硅的廉价工艺方面取得了重大进展。在寻找昂贵的带锯晶圆法的替代方法方面，进展非常有限。本建议中所述的想法可能有助于解决这些重要问题。提议的工艺从皮尔金顿玻璃工艺中获得灵感，这一工艺彻底改变了玻璃工业。主要目标是通过理论发展和对制造硅片的连续过程的实验验证来降低太阳能电力的成本。与目前的技术相比，所提出的工艺可以将太阳能组件的成本降低两倍，而且由于它是连续的，因此可以迅速扩大规模。子目标包括发展模型和控制理论的耦合流体流动，传热和凝固在水平带状生长的背景下。智力优势：本项目旨在为用高纯度多晶硅生产晶体硅晶圆的连续工艺发展科学基础。在这个过程中，pi计划将一个非常薄（小于0.3毫米）的硅片冻结在一个浮子室的硅熔体上。固体硅像冰一样漂浮在水面上，通过仔细控制，可以生产出适合太阳能电池的单晶硅片。然后，当硅原料以相同的速率连续馈送到该工艺时，片材可以连续取出。与昂贵的线锯工艺相比，生产成本较低，因为新工艺是连续的，不会造成硅的损失。pi计划研究熔融基板上冻结锋的稳定和控制，以及如何设计和控制具有多个界面（气体，固体，液体）的系统。这种类型的系统可能表现出几种不稳定性，需要主动控制来稳定系统。这些不稳定性包括结晶前沿的动力学，杂质如何分离和出口半月板的动力学。他们将开发多尺度过程模型和理论，能够分析过程设计和控制的稳定性特性。这些模型将使用从CMU大型试验工厂获得的实验数据与物理系统相匹配。同时的目标是发展一个理论如何建模，分析和控制复杂的流动和凝固问题。更广泛的影响：这项研究最重要的更广泛的影响是在替代能源领域——更经济地生产太阳能电池板。该研究为多尺度建模、凝固前沿稳定与控制以及多相流问题提供了新的方法。这些问题出现在许多应用领域，包括油漆的干燥，薄膜加工和涂层。

1438231 - YdstieThe technology for the direct conversion of sunlight to electricity using solar cells has not yet advanced to a point where it can have a significant impact in markets that do not benefit from government subsidies. The cost of solar cells is still very high and the technologies used to produce solar cells do not easily scale up. At the current rate of growth (20-30% per year) it will take many decades to build enough plants and infra-structure for solar electricity to displace fossil energy sources. Solar energy has so far not measured up to its potential due to the high cost of producing high purity silicon and mono-crystalline silicon wafers. Significant progress has been made in developing cheaper processes for making high purity poly-silicon in fluid bed reactors. Very limited progress has been made in finding alternatives to the expensive band-saw process for wafering. The ideas described in this proposal may contribute towards solving these important problems. The proposed process draws inspiration from the Pilkington glass process, which revolutionized the glass industry. The major objective is to reduce the cost of solar electricity by theoretical development and experimental verification of a continuous process for making silicon wafers. The proposed process could reduce the cost of a solar module by a factor of two relative to current technology and it can be rapidly scaled up since it is continuous. Sub-objectives include the development of models and control theory for coupled fluid flow, heat transfer and solidification in the context of horizontal ribbon growth.Intellectual Merit:This project aims to develop scientific foundations for a continuous process to produce crystalline silicon wafers from high purity poly-silicon. In this process the PIs plan to freeze a very thin (less than 0.3 mm) silicon sheet on top of a silicon melt in a float chamber. Solid silicon floats like ice on water and by careful control it is possible to produce mono-crystalline silicon sheets suitable for solar cells. The sheet can then be withdrawn continuously while silicon raw material is continuously fed to the process at the same rate. The production cost will be low relative to expensive wire saw processes since the new process is continuous and does not incur silicon loss. The PIs plan to study the stabilization and control of a freezing front on a molten substrate and how to design and control systems with several interfaces (gas,solid, liquid). Systems of this type may exhibit several types of instabilities and active control is needed to stabilize the system. These instabilities include the dynamics of the crystallization front, how impurities segregate and the dynamics of the exit meniscus. They will develop multi-scale process models capable and a theory capable of analyzing stability properties for process design and control. The models will be matched to a physical system using experimental data obtained from a large pilot plant at CMU. The simultaneous goal is to develop a theory for how to model, analyze and control complex flow and solidification problems.Broader Impacts:The most important broader impacts of this research are in the area of alternative energy - producing solar panels more economically. The research could lead to new methods for multi-scale modeling and stabilization and control of solidification fronts and multi-phase flow problems. These problems turn up in a number of application areas, including the drying of paints, film processing and coating.