SuperSilicon PV: extending the limits of material performance

煤炭、石油和天然气燃烧产生的二氧化碳排放导致了气候变化，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。这是必要的，因为可再生能源的成本高于化石燃料的成本。光伏发电（PV）的潜力是巨大的，每15分钟的阳光就能满足世界每年的能源需求。不幸的是，在大多数情况下，还没有光伏技术能够提供足够低成本的电力。硅光伏（PV）是一种主要的可再生技术，约占光伏市场的90%。目前业界的观点是，在可预见的未来，硅将继续主导市场。除了资金成本外，影响每千瓦时成本的关键参数是效率和工作寿命。电池的效率受限于它所能使用的那部分频谱。对于一个简单的（单结）电池，这个基本限制是~30%。许多旨在超越这一目标的想法已经被研究过，但低成本、长寿命和效率的基本组合被证明是非常难以捉摸的。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）硅的商业生产达到20%，其中电池的世界纪录效率为25.8%。从我们过去五年左右的硅材料研究项目的经验来看，我们相信有可能提高更便宜形式的硅的载流子寿命，从而提供高达22%的生产转换效率。对于家庭安装——电网平价被视为与公用事业供应商的价格相匹配——最新数据表明，这种效率足以在距离赤道60度的纬度上实现平价。该项目联合了三家英国硅光伏集团、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，共同研究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，使硅光伏发电以比传统发电厂更低的价格发电。硅的质量，以载流子寿命短为特征，限制了可以实现的效率的上限。电池加工已经足够成熟，只要原料质量高，就能制造出高效率的电池。简单地说，这个项目的目的是消除作为重组中心的缺陷，限制硅光伏电池的效率。我们正在开发新的杂质捕集和缺陷钝化方法，这些方法有可能去除现有工艺后残留的复合中心。该项目还将进一步了解硅缺陷的基本性质，包括纳米沉淀物在重组中的作用，阻碍硅基本载流子寿命达到的因素，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.