Elimination of Efficiency Degradation Mechanisms in Silicon Photovoltaic Solar Cells

光伏太阳能电池似乎肯定会对21世纪的世界能源需求做出重大贡献。目前，这种装置只能将福尔斯照射到地球表面的每平方米1千瓦的太阳辐射中的一小部分转化为电能。使用非集中太阳光的典型商业硅设备的效率低于15%，尽管实验室设备的效率高达24%。对于更高效率的第三代电池，已经提出了许多非常有趣的想法，但其中大多数距离大规模经济规模的商业实现还有很长的路要走。目前，90%的生产是基于硅片（直拉单晶或铸造多晶）。预计2010年使用现有硅技术的产量将达到26 GW的峰值。不幸的是，在其最初的几个小时的操作中，大多数硅太阳能电池遭受退化，该退化在效率降低10%之后相对稳定，即20%的电池变成18%的电池。在世界范围内总光伏功率损失的背景下，这是非常重要的。据信，效率的降低是由于硅中的缺陷反应，其中氧二聚体扩散到硼掺杂剂以形成强大的复合中心。这个问题不仅限于未来十年的商业设备，而且与一些最有前途的第三代（高效率）电池高度相关，这些电池使用硅作为有源结构的一部分。这项研究提案旨在通过在形成复合中心之前从硅中去除反应路径来消除降解过程。一个必要的先决条件，这是实现一个详细的理解的缺陷中心和它们的formation.We以前研究了氧二聚体，目前被认为是前体的重组中心。这些可以使用光学吸收测量来检测，理想情况下在低温（~ 10 K）下。初步工作表明，应该可以开发硅材料的处理，其将二聚体的浓度降低到成品电池中可忽略的水平，并且因为二聚体在正常操作温度下不形成，所以消除缺陷的形成。使用这种方法来保持间隙氧的浓度是非常可行的，间隙氧的浓度为硅提供机械强度，从而具有产量和成本效益。在这项工作中，复合中心将研究使用少数载流子拉普拉斯深能级光谱和其结构确定的单轴应力的应用。氧二聚体的反应将被研究为重组中心的形式，在真实的时间，使用光学吸收技术。这项工作将与太阳能硅的领先制造商之一MEMC，德国的Solarenergieforschung Hameln/Emmerthal研究所（ISFH）以及葡萄牙的阿韦罗大学合作完成，该研究所最近进行了大量关于太阳能电池退化的实验工作，该大学将在理论计算方面进行合作，以支持曼彻斯特的工作。

Photovoltaic Solar Cells seem certain to make a significant contribution to the world's energy needs in the 21st Century. At the present time such devices only convert a small part of the 1kW per square meter of radiation from the sun which falls on the earth's surface into electricity. Typical commercial silicon devices that use un-concentrated sunlight are less than 15% efficient although laboratory devices with efficiencies as high as 24% have been made. Many very interesting ideas have been put forward for higher efficiency 3rd generation cells but most of these are a very long way from commercial realization on a large economic scale. At the present time 90% of production is based on wafered silicon (Czochralski single crystal or cast poly-crystalline). The predicted production for 2010 using existing silicon technology will have a peak output of 26GW. Unfortunately in their initial few hours of operation most silicon solar cells suffer from degradation which stabilizes after a reduction in efficiency of 10% relative ie a 20% cell becomes an 18% cell. In the context of total photovoltaic power lost on a world scale this is very significant. It is believed that the reduction in efficiency is due to a defect reaction in the silicon in which oxygen dimers diffuse to the boron dopant to form a powerful recombination centre. The problem is not restricted to the commercial devices of the next decade but is also highly relevant to some of the most promising third generation (high efficiency) cells which use silicon as part of the active structure. This research proposal aims to eliminate the degradation process by removing the reaction path from the silicon prior to the formation of the recombination centre. An essential pre-requisite to this is to achieve a detailed understanding of the defect centres and their formation.We have previously studied the oxygen dimers which are currently thought to be the precursors of the recombination centre. These can be detected using optical absorption measurements, ideally at low temperatures (~10K). Preliminary work indicates that it should be possible to develop treatments of the silicon material which reduce the concentration of the dimers to a negligible level in the finished cell and, because the dimers do not form at normal operating temperatures, so eliminate the formation of the defect. It would be quite feasible using this approach to maintain the concentration of interstitial oxygen which provides mechanical strength to the silicon with consequent yield and cost benefits. In this work the recombination centre will be studied using minority carrier Laplace Deep Level Spectroscopy and its structure determined by the application of uniaxial stress. The reaction of the oxygen dimer will be studied as the recombination centre forms, in real time, using optical absorption techniques. The work will be done in collaboration with MEMC who are one of the leading manufactures of solar silicon, the Institut fr Solarenergieforschung Hameln/Emmerthal (ISFH) in Germany who have undertaken much experimental work recently on solar cell degradation and the University of Aveiro in Portugal who will collaborate on theoretical calculations to support the Manchester work.