Self-assembled organic photovoltaic materials

The development of renewable energy sources is an urgent problem and so large that many technologies will contribute. Solar photovoltaics can be expected to play a major role because of the abundance of solar energy, and the convenience of electricity as an energy source, but at present they contribute only a tiny fraction of the world's energy supply (e.g. ca. 0.1% in the US, according to the US Institute for Energy Research). The major reason for the very limited uptake is that current solar cells are much more expensive than generating power from fossil fuels. Organic semiconductors have the potential to solve this problem by providing a route to much lower cost solar cells. Organic semiconductors are pi-conjugated molecules and polymers, that can be processed from solution via low cost/high volume deposition techniques such as spin-coating, roll-to-roll processing and ink-jet and screen printing. This means that they can be used to make flexible thin film devices that are lightweight and portable.

We propose to develop new organic solar cell materials building on our promising initial results from novel cross-shaped molecules. The proposed materials have well-defined structures that pack together efficiently, giving improved charge transport. The key idea is to control this packing of materials so that they will "self-assemble" into the desired arrangement for efficient solar cells. To achieve this we will bring together teams of physicists and chemists and collaborate with leading groups at the National Renewable Energy Laboratory and Imperial College London.

Our world and way of life depends on an abundant supply of energy. Energy supply is a global issue and our existence depends on finding sustainable alternatives to fossil fuels. Solar power is the most abundant renewable energy source, but its take-up has so far been limited by its high cost. This cost could be greatly reduced by making solar cells from organic semiconductors, because these plastic-like materials can be made into solar cells by simpler processes than currently used for silicon solar cells. Our proposal addresses this challenge by developing new materials which self-organise in a way to improve charge transport and charge separation, thereby enabling better organic solar cells to be made.

Early beneficiaries of this research will include the UK organic electronics industry, such as companies developing improved materials and companies developing devices. Examples of these companies include Merck Chemicals (Southampton), Solar Press, Cambridge Display Technology, G24i Power (successor to G24i), Ossila and Eight19. As our proposal is focussed on materials development it is natural to have Merck, one of the world's leading chemical companies as a project partner (see letter of support), providing a route to market for materials that could then be brought to market by other companies. The improved materials we propose could improve the economic competitiveness of such companies, and help them bring organic solar cells to market.

After further development by companies such as those listed, our work will lead to solar cells that can be large area, low cost and flexible. Such cells would be used in a huge range of applications. Most obvious is generating electrical power for homes. However, smaller scale generation for portable electrical appliances such as mobile phones and tablets, and for off-grid devices such as some road signs are also important. The lightweight nature of the devices and their potential for flexibility would make improved organic solar cells very useful for recreation (camping, trekking), and integration into clothing and rucksacks.

The method of self-assembly to control molecular ordering, morphology and electronic properties that we propose to develop will also be expected to find other applications across materials science and engineering. This includes other areas of organic electronics such as field-effect transistors and companies working on them (e.g. Plastic Logic) but extends to the wider polymer and composite community.

Research staff on the project will benefit from the interdisciplinary interactions of physicists and chemists. This will be enhanced by research visits to the project partners at Imperial College and the National Renewable Energy Laboratory. The skills of such research collaboration will be valuable in a wide range of industrial sectors. In addition the researchers will acquire communication and project planning skills through reporting, conferences and public engagement activities.