SuperSilicon PV: extending the limits of material performance

由燃煤、石油和天然气排放的二氧化碳导致的气候变化，刺激了通过税收优惠或上网电价鼓励使用可再生能源的政策。这些都是必要的，因为可再生能源的成本高于从化石燃料中提取的能源。光伏(PV)的潜力是巨大的，每15分钟就有阳光提供世界上每年的能源需求。不幸的是，在大多数情况下，还没有一种光伏技术能够提供足够低成本的电能。硅光伏是一种主要的可再生技术，占光伏市场的90%左右。目前的行业观点是，在可预见的未来，硅将继续主导市场。除了资本成本外，影响每千瓦时成本的关键参数是效率和工作寿命。蜂窝的效率受到它可以使用的频谱部分的限制。对于简单的(单结)电池，这一基本限制是~30%。许多旨在超越这一点的想法已经被研究过了，但事实证明，低成本、长寿命和高效率的本质组合非常难以捉摸。由低成本多晶硅制成的商业模块的效率通常在13%到16%之间。使用高质量(更昂贵)硅的商业化生产达到了20%，其中电池的世界纪录效率为25.8%。根据我们在过去五年左右的硅材料研究项目中的经验，我们相信有可能提高廉价硅的载流子寿命，以提供更高的生产转换效率，约为22%。对于国内安装-电网平价被认为与公用事业供应商的价格匹配-最新数据表明，这种效率足以在距离赤道60度的纬度进行平价。该项目将三个英国硅光伏集团与四家材料制造商、一家主要电池制造商、两家材料表征公司和三家领先的国际大学集团联合起来，致力于解决硅光伏材料中一些最相关的问题。我们的目标是提供基础科学，使硅光伏发电能够以低于传统发电厂的价格发电。以少数载流子寿命为特征的硅的质量对所能达到的效率设置了上限。电池加工已经足够成熟，能够制造高效率的电池，前提是起始材料具有高质量。简单地说，这个项目的目标是消除作为复合中心的缺陷，并限制硅光伏电池的效率。我们正在开发新的杂质吸除和缺陷钝化的新方法，这些方法有可能消除现有工艺后残留的复合中心。该项目还将进一步了解硅中缺陷的基本性质，包括纳米沉淀物在复合中的作用，阻止达到硅的基本载流子寿命的因素，以及杂质-位错相互作用的热力学。

Climate change attributed to the emission of carbon dioxide from burning coal, oil and gas has stimulated policies which encourage the use of renewable energy via tax concessions or feed-in tariffs. These are necessary because the cost of renewable energy is more than that of energy derived from fossil fuels. The potential of photovoltaics (PV) is enormous, with sunlight delivering the world's annual energy needs every 15 minutes. Unfortunately, in most circumstances, no PV technology yet delivers adequately low cost electricity.Silicon photovoltaics (PV) are a major renewable technology, accounting for ~90% of the PV market. The present industry view is that silicon will continue to dominate the market for the foreseeable future. Apart from the capital cost, the key parameters affecting cost per kWh are efficiency and working life. The efficiency of a cell is limited by the portion of the spectrum it can use. For a simple (single-junction) cell this fundamental limit is ~30%. Many ideas which aim to go beyond this have been researched but the essential combination of low cost, long life and efficiency have proved very elusive. Commercial modules made from low cost multi-crystalline silicon generally have efficiencies in the range 13 to 16%. Commercial production using high quality (more expensive) silicon reaches 20%, where the world record efficiency for a cell is 25.8%. From our experience of silicon materials research projects over the past five or so years, we believe it will be possible to enhance the carrier lifetime of cheaper forms of silicon to provide substantially higher production conversion efficiencies of ~22%. For domestic installation - where grid parity is regarded as matching the utility supplier's price - latest figures suggest this efficiency is sufficient for parity at latitudes of up to 60 degrees from the equator.This project unites three UK silicon PV groups with four materials manufacturers, a major cell manufacturer, two materials characterisation companies, and three leading international university groups to work on some of the most pertinent issues in silicon PV materials. We aim to provide underlying science which will enable silicon PV to produce electricity at lower prices than traditional generating plants. The quality of silicon, as characterised by the minority carrier lifetime, places the upper limit on the efficiency that can be achieved. Cell processing is sufficiently mature to be able to make high efficiency cells provided the starting material is of high quality. Simplistically, the aim of this project is to remove defects which act as recombination centres and limit the efficiency of silicon PV cells. We are developing novel new methods of impurity gettering and defect passivation which have the potential to remove recombination centres which remain after existing processes. The project will also further understanding of the fundamental properties of defects in silicon, including the role of nano-precipitates in recombination, factors which prevent the fundamental carrier lifetime of silicon being reached, and the thermodynamics of impurity-dislocation interactions.