MESO-FRET: MEsoscopic SOlar harvesting via Fluorescence Resonance Energy Transfer

随着社会和经济需求的不断增长，我们需要尽快消除对化石燃料的依赖，以光伏(PV)技术为核心的太阳能解决方案的开发对国家和世界都具有战略意义。在英国，可再生能源部门约占总能源消耗的11%，政府承诺到2020年将这一贡献增加到15%，其中很大一部分预计将来自太阳能。要实现这一目标，将需要开发出提高能源转换效率和降低大规模应用成本的技术解决方案。太阳能转换具有尚未充分开发的潜力。目前使用的设备，硅太阳能电池，其效率限制在24%，尽管已经商业化并以具有竞争力的成本提供，但由于吸收带宽较窄，以及为扩大吸收带宽而采取的解决方案的昂贵，例如使用多层器件和太阳能跟踪器，仍受到限制。为了充分利用现有的潜力，除了对现有的光伏技术进行革命性的改变外，还需要用于下一代光伏的新材料。该项目的目标是开发新的光收集材料，即通过廉价的方法获得的混合系统，可以用于发光太阳能聚光器(LSC)。LSC是一种可行的解决方案，也是对半导体PV的经济有效的补充，可以提高太阳能电池的产量。它们含有发光染料，可以在设备的大片区域捕获太阳光能量，并通过波导效应将其集中到连接太阳能电池的边缘。每个电池暴露在照射到它身上的阳光高达10倍，这意味着面积更小的硅电池更少，从而降低了成本。同时，增加入射光子密度，LSCs可以使每个电池获得的电能增加40倍以上，太阳能电池板的转换效率提高50%。然而，尽管LSCs前景看好，但到目前为止，由于缺乏覆盖整个太阳光谱的合适发射体、限制了最大可能集中系数的自吸收损失以及在长时间使用几个月内漂白的光学部件的短寿命，LSCs的广泛使用受到了阻碍。拟议的研究解决了这些限制，并旨在为LSCs设计新的太阳能天线，其关键条件是：(I)全色性，以确保在太阳光谱上的宽带吸收，(Ii)高收集效率，通过对染料的优化组织，通过被称为FRET(荧光共振能量转移)的非常快速和高效的过程来转移收获的能量来最小化再吸收损失并最大化能量集中，该过程与自然光合作用系统所利用的过程相同；(Iii)耐久性，通过封装到主-客体结构中，以增强对光降解和热/机械应力的稳定性；以及(Iv)成本效益，通过使用地球丰富的材料和自组装技术来使技术可持续，这通常需要比传统合成更温和的条件。该项目的目标是提供一种综合的方法，其中高效采光的所有要求都由一种材料来满足。为了实现这一点，新的天线是从分子尺度上设计的，使用由地球上丰富的元素制成的光学元件，并组织成规则的结构，反映从分子域到介观尺度的顺序，空间域最大可达1微米，这是拟议的太阳能收集器的大小。因此，首字母缩写为Meso-fret。

The development of solar energy solutions, with photovoltaic (PV) technologies in primis, is of strategic importance for the nation and worldwide, since the societal and economical demands constantly grow and we need to eradicate soon our reliance on fossil fuels.In the UK, the renewables sector covers about 11% of the total energy consumption and the government is committing to increase this contribution to 15% by 2020 with a large part that is expected to come from solar power. Meeting this target will require the development of technological solutions with increased energy conversion efficiency and at reduced costs for large scale applications.Solar conversion has a potential that is not being fully exploited yet. Currently used devices, silicon solar cells, have efficiencies limited to 24% and, although already commercialised and available at competitive costs, still suffer from limitations due to the narrow absorption bandwidth and the expensiveness of the solutions adopted to enlarge it, such as use of multi-stacked devices and solar trackers. To make full use of the available potential, in addition to make evolutionary changes to existing PV technologies, new materials for next-generation PVs are needed.This project targets the development of new light harvesting materials, hybrid systems obtained by inexpensive methodologies that can be used in luminescent solar concentrators (LSCs). LSCs are a viable solution and cost-effective complements to semiconductor PVs that can boost the output of solar cells. They contain luminescent dyes that capture sunlight energy over a large area of the device and concentrate it by wave-guide effects to the edges, where a solar cell is interfaced. Each cell is exposed up to 10 times more of the sunlight that hits it, meaning fewer silicon cells with reduced areas and thus reduced costs. At the same time, increasing the incident photon density, LSCs could increase the electrical power obtained from each cell by a factor of over 40 and the conversion efficiencies of solar panels by 50%. Despite their promise, however, the wide use of LSCs has so far been hindered by the lack of suitable emitters that would cover the full solar spectrum, by self-absorption losses that restrict the maximum possible concentration factor and by the short longevity of the optical components that photo-bleach within a few months of prolonged use.The proposed research tackles these limitations and aims at designing new solar 'antennae' for LSCs that possess the key requisites of: (i) panchromaticity, to ensure broadband absorption over the solar spectrum, (ii) high harvesting efficiency, by means of an optimal organisation of the dyes that minimises re-absorption losses and maximises energy concentration through the transfer of the harvested energy by a very fast and efficient process known as FRET (Fluorescence Resonance Energy Transfer), the same that is utilised by natural photosynthetic systems, (iii) durability, by encapsulation into a host-guest structure, to enhance stability against photo-degradation and thermal/mechanical stress, and (iv) cost-effectiveness, to render the technology sustainable, through the use of earth abundant materials and self-assembly strategies, which typically require milder conditions than traditional synthesis.The ambition of this project is to provide a comprehensive approach, where all requirements for efficient light harvesting are met by one material. To enable this, the new antennae are engineered from the molecular scale, using optical components made of earth-abundant elements, and organised into regular structures that reflect the order from the molecular domain to the mesoscopic scale, the space domain up to 1 micron, that is the size of the proposed solar harvesters. Hence, the acronym MESO-FRET.