Nitride Photovoltaic Materials for Full Spectrum Utilization

到2050年，全球人口预计将达到120亿，加上经济的适度增长，尽管能源效率有所提高，但全球能源消耗总量预计将从目前的约13太瓦增加一倍以上，达到约28太瓦（10亿瓦）。为了限制或减少二氧化碳水平，大部分额外的能源必须来自无碳资源，其中最大的是太阳能（100,000太瓦）。然而，太阳能必须以合理的低成本转化为可用的形式。事实上，在英国，由于太阳能发电的成本相对较高，最近可再生能源发电的增长主要依赖于风能的使用。降低太阳能发电成本最有希望的方法之一是使用小面积高效电池，光通过低成本的大面积塑料透镜集中在上面。迄今为止，效率最高的太阳能电池由含有砷化物和磷化物的三结III-V半导体器件组成。这些材料的带隙不能与太阳光谱的波长范围相匹配，限制了可获得的最大效率。提出的工作将为未来全光谱超高效率光伏的演示开发氮化物材料。与目前最先进的技术相比，氮基太阳能电池与聚光器技术有望在效率和成本方面取得重大进展。这种潜力是新发现的氮化铟（InN）窄带隙的结果，使得三元合金氮化铟镓和氮化铟铝的带隙跨越整个太阳光谱（InGaN为0.6至3.4 eV， InAlN为0.6至6.2 eV）。由这些材料系统制成的太阳能电池预计将达到双结电池50%的最大理论效率。这几乎是当前三结太阳能电池设备效率的两倍。具有三个或更多结的氮基电池可以达到接近60%的效率。然而，对这些材料的研究还不是很先进，材料质量仍在优化中。InGaN和InAlN的外延生长仍在继续发展，项目合作伙伴正在进行改进，他们将为拟议的工作提供样品。在这个项目中，将进行结构、光学和电学表征的综合计划，以优化这些合金在氮基光伏器件中的应用。与这些活动同时，还将对iii -氮化物结构进行实验，以实现可重复的n型和p型掺杂，开发隧道结，确定光伏性能缺陷的作用，并优化金属接触和透明导电氧化物太阳能电池窗口。太阳能电池建模将使用从实验中确定的材料参数进行，以产生高效氮化太阳能电池的优化设计，并研究新的集成光/电太阳能电池设计，绕过传统的电流和晶格匹配约束。拟议中的计划最终将使英国在氮化物广泛领域的极高专业知识扩展到包括用于低成本，低碳能源发电的富铟氮化物合金。

With the global population projected to reach 12 billion by 2050 coupled with moderate economic growth, and despite increased energy efficiency, the total global energy consumption is estimated to more than double to ~28 TW (1 billion billion watts) from the current use of ~13 TW. To cap or reduce carbon dioxide levels, most of this additional energy must come from carbon-free sources, the largest of which is solar energy (100,000 TW). However, solar energy has to be converted into a useable form at reasonably low cost. Indeed, in the UK, recent increases in renewable energy generation have mostly relied upon increased use of wind power due to the relatively high cost of solar power. One of the most promising approaches to reducing the cost of solar power, is to use small-area high efficiency cells with light concentrated on them by low cost, large-area plastic lenses. The highest efficiency solar cells to date consist of three junction III-V semiconductor devices containing both arsenides and phosphides. The failure of the band gaps of these materials to match the wavelength range of the solar spectrum limits the maximum efficiency obtainable.The proposed work will develop nitride materials for future demonstration of full spectrum super-high efficiency photovoltaics. Nitride-based solar cells with concentrator technologies promise to deliver significant advances in efficiency and reductions in cost over the current state-of-the-art. This potential is a result of the newly discovered narrow band gap of indium nitride (InN), making the band gaps of the ternary alloys indium gallium nitride and indium aluminium nitride span the entire solar spectrum (0.6 to 3.4 eV for InGaN and 0.6 to 6.2 eV for InAlN). Solar cells made from these material systems are predicted to attain the maximum theoretical efficiency of a double-junction cell of 50%. This is almost twice as efficient as the current generation of triple-junction solar cell devices. Nitride based cells with three or more junctions could achieve efficiencies approaching 60%. However, research on these materials is not very advanced and the material quality is still being optimised. The epitaxial growth of InGaN and InAlN continues to be developed, with improvements being made by the project partners who will provide samples for the proposed work. In this project, a comprehensive programme of structural, optical and electrical characterisation will be undertaken to optimise these alloys for application in nitride-based photovoltaic devices. In parallel with these activities, experiments will also be undertaken on III-nitride structures to achieve reproducible n- and p-type doping, to develop tunnel junctions, to determine the role of defects in photovoltaic performance, and to optimise metal contacts and transparent conducting oxide solar cell windows. Solar cell modelling will be performed using material parameters determined from the experiments to produce optimized designs for high-efficiency nitride solar cells and to investigate new integrated optical/electrical solar cell designs which circumvent traditional current and lattice matching constraints. The proposed programme will ultimately allow the UK's exceptionally high expertise in the broad area of nitrides to be extended to include indium-rich nitride alloys for low cost, low carbon energy generation.