Polymer / fullerene photovoltaic devices: new materials and innovative processes for high-volume manufacture

The harvesting of sunlight has the potential to revolutionize the way mankind generates electricity. At present however, only a small fraction (0.02% in 2008) of the world's total electrical power is generated using sunlight. Photovoltaic (PV) installations based on crystalline silicon are an increasingly popular way of generating electricity from solar-radiation, however such installations suffer from a relatively long pay-back time resulting from their high cost of manufacture. There is thus growing interest in the development photovoltaics based on organic (polymeric) materials (OPV) that can in principle be produced at low-cost, over very large areas utilizing solution-based processes that do not require a large energy input. At present however, even the best lab-based OPVs have an efficiency that is significantly lower than that of standard crystalline silicon (~8% compared with ~18%), coupled with a relatively short operational lifetime - attributes that have partly precluded their commercialization. There is nevertheless great interest in exploring the scale-up of OPVs, despite the fact that no common consensus has been reached on the best route to deposit multilayer architectures at high-speed. This problem is compounded by the fact that many of the materials that have the highest efficiency in OPV devices often have rather low solubility; properties that limit their application in high-speed manufacture processes. Addressing these issues lies at the heart of our proposed research. Firstly, we will engineer the chemical structure of state-of-the-art low energy-gap donor polymers to significantly improve their solubility and processability. We will then explore the deposition of such materials into OPVs using spray-based techniques. The thin-films formed will be characterized using high-resolution electron microscopy together with X-ray and neutron-scattering. The project team we have assembled for this task have leading expertise in organic-electronics, polymer-synthesis, polymer-physics and practical manufacturing processes. Our project is significantly strengthened by funds from the European Regional Development Fund (Project Mercury) to purchase an automated aerosol deposition system and fund postdoctoral and postgraduate researchers. We have ready route for commercialization via our (unfunded) links with a TSB-funded project that intends to develop OPVs for transparent window-glass applications. We anticipate the outcome of our work will be a materials set and a scalable process for high speed OPV manufacture.We will gain impact for our work through showcasing scaled-up OPV devices at the Sheffield Solar Farm and by interacting with artists and designers who wish to use organic photovoltaics in their work. We will also gain valuable support and publicity for our work through 'Project Sunshine'; a flagship project at Sheffield that promotes research into the utilization of solar energy to solve problems related to mankind's growing energy-needs and food-production in a time of growing climate uncertainty.

There are significant commercial opportunities for the development and manufacture of solution-processable photovoltaic devices. These range to fully-flexible panels, to building-integrated systems. There is presently a window of opportunity for the development of valuable IP and enabling technology in this area that the UK must exploit in the face of significant international competition. Our project directly addresses the development of a high-volume manufacturable process to create organic photovoltaic (OPV) devices and will be important for driving new industrial opportunities. We are working informally with a TSB-funded consortium comprising PETEC, Pilkington, Polysolar and Solvay Ltd who are looking to manufacture semi-transparent OPV on window glass. Our work will provide basic underpinning science to this consortium, and will therefore find a very natural route to commercialization. In addition to the commercial opportunities of OPV manufacture, there are significant societal benefits to our work. Many rural communities in Africa, India and Latin America do not have access to electricity via a grid system as a result of limited basic infrastructure or unfavourable geographic location. The widespread deployment of cheap, light-weight, flexible and rugged photovoltaic panels to such disadvantaged communities could, for example provide refrigeration of medicines in remote clinics, or light for children to read and study in the evening. Enabling such communities to generate their own solar electricity could therefore be a very significant driver to reduce poverty and drive economic development. Low-cost PV panels that can be manufactured in large volumes are also an attractive proposition for people in developed countries, as they offer the potential for significant savings in domestic energy bills, and could also contribute to reduced CO2 emissions. The project will also have impact on a much shorter timescale through the high-level training that it will offer to the PDRAs and PG students that we will employ. Training will be in the areas of chemical synthesis of conjugated polymers, materials science including characterization and the fabrication and evaluation of photovoltaic devices. Given the very significant interest in photovoltaics (and materials research more broadly), the demand for researchers having such skills is likely to be high. The Faculty of Science at the University of Sheffield have shown very strong commitment to solar-energy research via its flagship project called 'Project Sunshine' and we will naturally gain national and international publicity as a result. Our proposed project will be closely linked to a PV research station called the Sheffield Solar Farm (SSF). The SSF will act as a demonstration centre for new and emerging photovoltaic technologies and will host a number of open days each year for schoolchildren and the general public. The SSF has a web-site that displays the current power output and efficiencies of all the PV devices currently under-test, together with a log of their performance. We will site the best spray-coated OPV modules developed in the project at the SSF. This will offer an excellent opportunity for us to show-case our OPV devices to the public and to a wide-range of potential industrial partners. We will collaborate with dress designers and sculptors who are interested in using flexible organic photovoltaics in clothing and jewelry. We are confident that this will attract mainstream media attention. We have an excellent track record in publishing research in high-impact journals, and we believe that the academic impact of our work will be high as our project combines basic physics, synthetic chemistry, material science with the development of practical manufacturing techniques. All the senior academic staff in our consortium have a significant media profile and will work actively in taking our research talks into schools and the local community.