Light and Elevated Temperature Induced Degradation of Silicon Solar Cells

减少二氧化碳排放的重要性和紧迫性已经得到了广泛的宣传。发电占全球碳排放量的38%。在全球变暖的所有来源中，从技术上讲，发电可能是最容易被无碳能源取代的。利用光伏效应产生的太阳能发电，也就是我们所说的太阳能PV，在15年前还是一个非常小众的应用。然而，在过去的十年中，硅太阳能光伏技术以惊人的速度发展，以至于今天它是赤道45度以内大多数国家最便宜的发电方式。同样重要的是，产量每增加一倍，制造成本就会下降24%，比大多数产品都要快得多。目前，太阳能光伏发电仅提供了全球2.6%的电力（以千瓦时计），尽管在一些国家这一比例更高（如德国7.9%，印度5.4%）。有许多因素推迟了这项技术的采用。在像英国这样的国家，最大的困难是间歇性的，在这些国家，峰值负荷与峰值太阳能输出不匹配，需要抽水蓄能水电或其他快速启动发电，这增加了成本。在热带和亚热带国家，太阳能发电与负荷匹配得更好，正是这些国家的电力需求增长最快。然而，总的来说，人们不愿意投资太阳能，部分原因是太阳能被认为是一种未经验证的技术，以及关于资本密集型系统的长期可靠性的问题，其成本基于预计寿命为100 - 25年。众所周知，硅太阳能电池会降解。有两种重要的商业机制。一个是由于硼和氧的反应发生得非常快，在运行的头24小时内效率降低了2%。专家们对这一点已经有了充分的了解，他们正在开发最小化影响和展示稳定性的方法。另一种机制称为“光和高温降解”（LeTID）。它需要几个月甚至几年的时间才能产生2%到5%的降解。光照强度越高，温度越高，降解速度越快，尽管不同材料和太阳能电池设计之间存在很大差异，尽管有很多行为数据，但这些差异根本无法理解。该项目的目的是发展对降解机制的基本认识，测试减少或消除LeTID的拟议方法，并利用我们对所涉及的降解机制的了解制定有意义的加速寿命试验。实验工作将在曼彻斯特进行，使用我们在曼彻斯特和新南威尔士大学（澳大利亚）制造的测试设备。使用的主要技术将是曼彻斯特和澳大利亚国立大学（堪培拉）的光学、化学和电学测量，并由阿威罗大学（葡萄牙）的建模工作提供支持。这些将包括寿命光谱、深能级瞬态光谱和变体、导纳光谱、低温光发光、时间分辨光发光、拉曼光谱、氢测量和二次离子质谱。材料和设备样品将由活跃在硅太阳能领域的两家制造商提供。

The importance and urgency of reducing carbon dioxide emissions has received much publicity. Electricity generation is responsible for 38% of carbon emissions world wide. Of all sources of global warming electricity generation is probably, technologically, the most easily replaced by carbon free sources. Electricity from sunlight using the photo-voltaic effect, which we will refer to as solar PV, was very much a niche application as little as 15 years ago. However in the last decade silicon solar PV technology has developed with astonishing speed so that today it is the cheapest form of electricity generation in most countries within 45 degrees of the equator. Equally importantly the cost of manufacture is decreasing by 24% for each doubling of production volume, much faster than most products. At the moment Solar PV provides only 2.6% of the world's electricity (in kWh) although a higher percentage in some countries (eg 7.9% in Germany, 5.4% in India). There are a number of factors which delay the take up of this technology. The biggest difficulty is intermittency in countries like the UK where peak load does not match peak solar output necessitating pumped storage hydro or other rapid start up generation which adds to the cost. In tropical and sub-tropical countries solar generation matches the load much better and it is these countries in which electricity demand is increasing most rapidly. However in general there is a reluctance to invest in Solar which in part is due to Solar being regarded as an unproven technology and questions regarding long term reliability of a capital intensive system with a costing based on a projected life of >25 years. It is well known that silicon solar cells degrade. There are two commercially important mechanisms. One is due to a reaction involving boron and oxygen which happens very quickly reducing the efficiency by ~2% in the first 24 hours of operation. This is well enough understood for specialists to be on the way to developing ways of minimising the effect and demonstrating stability. The other mechanism is called "light and elevated temperature degradation" (LeTID). It takes months or sometimes years to produce a degradation of between 2 and 5%. The higher the light intensity and the higher the temperature the faster the degradation although there are large variations between different materials and solar cell designs which are not at all understood despite much behavioural data.The aims of this project are to develop a fundamental understanding of the degradation mechanism, to test proposed methodologies for reducing or eliminating LeTID and to use our understanding of the degradation mechanisms involved to develop meaningful accelerated life tests. Experimental work will be done in Manchester using test devices fabricated by us in Manchester and by the University of New South Wales (Australia). The prime techniques used will be optical, chemical and electrical measurements in Manchester and the Australian National University (Canberra) supported by modelling work at the University of Aveiro (Portugal). These will include lifetime spectroscopy, Deep Level Transient Spectroscopy and variants, admittance spectroscopy, low temperature photo-luminescence, time resolved photo-luminescence, Raman spectroscopy, hydrogen measurements and Secondary Ion Mass Spectroscopy. Materials and devices samples will be supplied by two manufactures active in the silicon solar field.