Proof of Concept for enhancing single-junction and tandem concentrator cells by photon recycling

通过光子回收增强单结和串联聚光器电池的概念验证

• 批准号: EP/F008589/1
• 负责人: Keith William John Barnham
• 金额: $ 8.92万
• 依托单位: Imperial College London
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2007
• 资助国家: 英国
• 起止时间: 2007 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FF008589%2F1
• 关键词: Proof; Concept; enhancing; single; junction

This proposal concerns a novel type of photovoltaic (PV) solar cell. The threat of global warming is one reason for the rapid expansion in this low-carbon technology. In recent years, world-wide, solar cell manufacturing has been increasing exponentially by 47% each year. The development of higher efficiency cells will help this expansion continue. The Imperial Quantum Photovoltaic Group (QPV) have been collaborating with the EPSRC National Centre for III-V Technologies on an EPSRC grant GR/S81933 which has developed a novel, nano-structured solar cell known as the strain-balanced quantum well solar cell (SB-QWSC). Their primary achievement was to demonstrate a cell which operates at a 27% efficiency which is approximately twice the efficiency of the current Si based PV cells and close to the single junction cell efficiency record of 27.8%. The SB-QWSC is made from GaAs based alloys using the quantum well (QW) technology which underpins modern communication devices such as the laser, LED and the amplifier in mobile phones. The rapid PV market expansion has lead to a silicon feed-stock shortage, so cells based on a different material system and production technology are important if the expansion is to be maintained. As GaAs based cells are expensive a number of companies are developing light-concentrating systems, in which lenses or mirrors focus sunlight onto the cells. This way it is possible to reduce the area of the expensive PV cell by about 1/500. This leads to a major price reduction. The QWs give the cell a wider spectral range without introducing crystal dislocations. Both features give the SB-QWSC a number of advantages in concentrator applications over the tandem or triple junction GaAs based cells which were designed for use in space. The absence of dislocations means the SB-QWSC will have a longer device lifetime than the highest efficiency version of the multi-junction cell. At the same efficiency a SB-QWSC will outperform a conventional tandem cell because it does not require a tunnel junction to connect the cells. The wider spectral range of the QW cell results in significantly more electrical energy being harvested over a year due to the seasonal and daily spectral variation of the sunlight. The QPV group have also demonstrated that when the SB-QWSC is incorporated in a tandem cell the wider spectral range leads to a higher cell efficiency. This enhancement is such that in Madrid, where there is a guaranteed price for PV electricity fed into the grid, the energy savings are as large as the system capital cost over the anticipated 25 year lifetime. In the course of project GR/S81933 the QPV group unexpectedly observed that the SB-QWSC was exhibiting a phenomenon known as photon recycling when operating at high concentration. They had already demonstrated that the quantum well material was of such good quality that the only loss mechanism which operates at high light levels was the unavoidable loss of the current carriers back into photons of light. They observed that, when a mirror, known as a distributed Bragg reflector (DBR) is grown under the quantum wells, some of these lost photons are reflected back into the QWs. Here they are absorbed like the incident sunlight, add to the current and enhance the efficiency. The aim of this project is to study this effect further and see if it can be exploited commercially. We will investigate the use of deeper QWs, different DBRs and transparent substrates to maximise the effect in both single-junction and tandem cells. The maximum efficiency gain which might be achieved is ~ 4%, which is similar to that discussed above, i.e. giving savings similar to the system cost in a sunny location with a guaranteed price for PV electricity. This project should provide very significant added value to the second generation products of or our new company QuantaSol and also strengthen the intellectual property.

该提案涉及一种新型光伏（PV）太阳能电池。全球变暖的威胁是这种低碳技术迅速发展的原因之一。近年来，全球太阳能电池制造业每年以 47% 的速度呈指数级增长。更高效率电池的开发将有助于这种扩张的继续。帝国量子光伏集团 (QPV) 一直与 EPSRC 国家 III-V 技术中心合作，获得 EPSRC 拨款 GR/S81933，开发了一种新型纳米结构太阳能电池，称为应变平衡量子阱太阳能电池 (SB-QWSC)。他们的主要成就是展示了一种以 27% 效率运行的电池，大约是当前硅基光伏电池效率的两倍，接近单结电池效率记录 27.8%。 SB-QWSC 由 GaAs 基合金制成，采用量子阱 (QW) 技术，该技术支撑着现代通信设备，如激光器、LED 和手机中的放大器。光伏市场的快速扩张导致硅原料短缺，因此如果要维持扩张，基于不同材料系统和生产技术的电池非常重要。由于砷化镓电池价格昂贵，许多公司正在开发聚光系统，其中透镜或镜子将阳光聚焦到电池上。这样就可以将昂贵的光伏电池的面积减少约1/500。这导致价格大幅下降。量子阱为电池提供了更宽的光谱范围，而不会引入晶体位错。与专为太空使用而设计的串联或三结 GaAs 电池相比，这两个功能使 SB-QWSC 在聚光器应用中具有许多优势。不存在位错意味着 SB-QWSC 的器件寿命将比最高效率版本的多结电池更长。在相同效率下，SB-QWSC 将优于传统串联电池，因为它不需要隧道结来连接电池。由于太阳光的季节性和每日光谱变化，QW 电池的光谱范围更宽，因此一年内可以收获更多的电能。 QPV 小组还证明，当 SB-QWSC 集成到串联电池中时，更宽的光谱范围可带来更高的电池效率。这种增强使得在马德里，光伏发电并入电网的价格有保证，所节省的能源与预期 25 年使用寿命内的系统资本成本一样大。在 GR/S81933 项目过程中，QPV 小组意外地观察到 SB-QWSC 在高浓度运行时表现出一种称为光子回收的现象。他们已经证明，量子阱材料的质量非常好，在高光水平下运行的唯一损失机制是电流载流子不可避免地损失回光子。他们观察到，当在量子阱下生长一面称为分布式布拉格反射器（DBR）的镜子时，其中一些丢失的光子会反射回量子阱中。它们在这里像入射阳光一样被吸收，增加电流并提高效率。该项目的目的是进一步研究这种效应，看看是否可以将其用于商业用途。我们将研究使用更深的 QW、不同的 DBR 和透明基板，以最大限度地提高单结和串联电池的效果。可能实现的最大效率增益约为 4%，这与上面讨论的类似，即在保证光伏发电价格的情况下，节省的成本与阳光充足的地方的系统成本类似。该项目将为我们新公司 QuantaSol 的第二代产品提供非常重要的附加值，并加强知识产权。