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

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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.