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，因此，以光伏（PV）技术为基础的太阳能解决方案的开发对国家和全球具有战略重要性。在英国，可再生能源部门占总能源消耗的11%左右，政府承诺将这一比例提高到15%。到2020年，预计其中很大一部分将来自太阳能。要实现这一目标，就需要开发出提高能源转换效率、降低大规模应用成本的技术解决方案。太阳能转换的潜力尚未得到充分开发。目前使用的设备，硅太阳能电池，效率限制在24%，虽然已经商业化并以有竞争力的成本获得，但由于吸收带宽窄和扩大它所采用的解决方案的昂贵性，例如使用多堆叠设备和太阳能跟踪器，仍然受到限制。为了充分利用现有的潜力，除了对现有的光伏技术进行渐进式变革外，还需要新材料用于下一代光伏。该项目的目标是开发新的集光材料，通过廉价的方法获得可用于发光太阳能聚光器（LSC）的混合系统。LSC是一种可行的解决方案，是半导体PV的经济有效的补充，可以提高太阳能电池的输出。它们含有发光染料，可以在设备的大面积上捕获太阳能，并通过波导效应将其集中到太阳能电池连接的边缘。每个电池暴露的阳光是照射它的阳光的10倍，这意味着面积减少的硅电池更少，从而降低了成本。同时，增加入射光子密度，LSC可以将每个电池获得的电力增加40倍以上，太阳能电池板的转换效率提高50%。然而，尽管LSC有希望，但到目前为止，LSC的广泛使用受到缺乏覆盖整个太阳光谱的合适发射器的阻碍，由于限制最大可能的聚集因子的自吸收损耗以及由于光致发光的光学部件的短寿命，这项拟议中的研究解决了这些限制，旨在为LSC设计新的太阳能“天线”，关键字：（i）全色性，以确保在太阳光谱上的宽带吸收，（ii）高收集效率，通过染料的最佳组织，通过被称为FRET的非常快速和有效的过程转移收集的能量，使再吸收损失最小化并使能量集中最大化（荧光共振能量转移），与天然光合系统所利用的相同，（iii）耐久性，通过包封到主-客体结构中，提高对光降解和热/机械应力的稳定性，以及（iv）成本效益，通过使用地球上丰富的材料和自组装策略，使技术可持续发展，这通常需要比传统合成更温和的条件。其中一种材料满足有效光捕获的所有要求。为了实现这一点，新的天线是从分子尺度设计的，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，空间域高达1微米，这是拟议的太阳能收集器的大小。因此，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.