EXPLORER; Excitonic Polymer Organic Devices for Energy

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.

The current global lighting market (commercial and domestic) is $80 Billion and based on historical evidence is expected to continue growing at approximately 3% per annum. With rising energy costs and political drivers to reduce CO2 production, organisations and consumers are becoming increasingly interested in more energy efficient lighting solutions. For example, lighting in the NHS accounts for ~37% of the total electricity bill and globally 20% of all electrical energy produced is consumed for artifical lighting. The introduction of high effiency organic solid-state lighting products would have a dramatic impact on energy consumption. The current road map is to demonstrate the manufacturability of low voltage PLED devices suitable for the eventual replacement (2013) of fluorescent lighting systems, and when linked to central energy storage systems and renewable power sources, offers potential for non-metered lighting systems, i.e. your lighitng is free after installation. This will ensure the UK can produce the lighting technology for tomorrow and will allow significant progress towards the Kyoto targets set for 2020. The US DoE has reported that the potential benefits from developing solid-state lighting (SSL) are: (i) by 2025 US national electricity consumption for lighting could be reduced by more than 300 TWh, which corresponds to 8% of electricity production in 2002; (ii) the cumulative savings on US consumer electricity bills could be >$125B between 2005 and 2025; (iii) the building of more than forty 1000 MW power stations could be deferred, contributing to a cleaner environment and more reliable grid operation. If an efficiency of 120 lm/W is achieved (predicted for ca. 2015) then about 30% of the electrical energy used for general lighting purposes in Europe could be saved. That translates into savings of 40 GW electrical peak power supply or an equivalent of 50 Million tons of CO2 per year. By 2025, SSL could reduce the global amount of electricity used for lighting by 50%! SSL light sources are also free of poisonous heavy metals, e.g. mercury, and as a consequence are much easier to dispose of, i.e. the PLED lamp can simply be thrown back into the glass furnace and recycled. These overall benefits accrued from the transfer to SSL would have massive social impact in all major Western countries. This project will help to maintain the UK at the forefront of this positive social and environmental revolution. There will be significant social impact on employment in the construction, electrical installation and lighting manufacturing industries as building and interior designs adapt to the new lighting technology and existing businesses are replaced by new ones exploiting the advantages of OLED lighting. Further benefit to UK PLC will come from future interaction with the vibrant UK design sector. The myriad possibilities opened up by a combination of high value design concept lighting and flexible lighting manufacture can only be of benefit to the economy. Thus in the mid- to long-term this project, if successful, will be seen to make a major impact on the achievement of these goals. A succesful outcome from this project will provide the polymers required to utilise a fully phosphorescent white PLED architecture. This will yield devices which can attain both an efficacy of >40 lm/W (without outcoupling) and a colour temperature of 4000K. This will enable polymer solid state lighting to better current fluorescent luminaires, enable PLED solid state lighting to move to commercialisation and start realise the major benefits highlited above. In so doing this project will have a major impact on the UK economy and environment.