EXPLORER; Excitonic Polymer Organic Devices for Energy

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We propose three adventurous, cross-disciplinary projects within the area of energy research. The past decade has seen an upsurge in interest in the field of organic electronics. Devices such as light-emitting displays and chemical and physical sensors are already on the market - and probably in your home and in your pocket - while others, such as solar cells are developing fast. The motivation is the reduced cost, ease of manufacture, large-area capability and the enhanced efficiency which is possible using these new technologies. However, a lot more research is still needed. This study will unite: (i) the synthesis of new materials, (ii) detailed spectroscopic characterisation (iii) device fabrication and measurements of performance, and (iv) theoretical calculations. The team will study materials whose properties are systematically changed with the aim of enhancing their performance in three areas. Energy transfer within and between molecules is a central theme.(i) More efficient display technologies and new types of lighting. Organic light-emitting devices (OLEDs) use small molecules or polymers which are built up from conjugated rings and pi-electrons to convert electrical energy into visible light. The innovative feature in this project is the use of metal complexes of molecules which emit from a doublet state (i.e. when the metal has one unpaired electron). This is an idea which has not been tested before in OLEDs and, if successful, it could overcome a major limitation of the current technology. Existing devices use molecules with a singlet or triplet state and this limits their efficiency. In particular, our strategy could lead to more efficient blue emitters. This is essential for full-colour displays and for producing white light in lighting applications. New efficient sources of white light are urgently needed as lighting accounts for more than 20% of the UK's energy consumption. (ii) Enhancing Performance of Organic Solar Cells. It is well known that conjugated organic molecules can capture sunlight and convert it into electricity. However, the power conversion efficiency is very low (only about 6%) i.e. 94% of solar radiation does not lead to electric current. We will explore an innovative way of improving this efficiency. When the molecules in a solar cell absorb sunlight, it is crucial to channel this energy between molecules in a precise way to get an efficient output of electricity. A major problem is how to prevent the charged molecular states from recombining (quenching) - a process which does not lead to electricity. We will explore the use of low-energy triplet states to overcome this problem. The advantage of triplet states is that they have longer lifetimes and can therefore move further within the molecules and are less likely to recombine. A new device architecture will be developed that could harness triplets and generate electricity more efficiently.(iii) Reducing atmospheric carbon dioxide. We are all aware of the huge environmental problems of the increasing levels of carbon dioxide in the atmosphere. We propose a new approach to converting carbon dioxide into fuel feedstocks. The principle is this: conjugated polymers absorb light efficiently and then transfer their electrons to nanoparticles or nanotubes. Instead of producing current (as in a solar cell) these charges will be used to convert carbon dioxide into useful fuel molecules, such as methane or ethanol (which could be used instead of oil or coal). Our scheme for achieving this uses organometallic complexes which can capture carbon dioxide on the surface of the nanoparticles.We are in contact with industrial collaborators who will provide input to facilitate future exploitation of promising results.