Solar cells fabricated using a “spray painting” process could provide a cost-effective alternative to conventional silicon-based cells and make photovoltaic technology available to people in developing countries. Researchers from the universities of Sheffield and Cambridge have collaborated to devise a method of spray-coating a photovoltaic active layer using an air-based process — similar to spraying regular paint from a can. The cheaper technique can be used for mass production and perhaps one day could be used on glass in buildings or car roofs. “Spray coating is currently used to apply paint to cars and in graphic printing,” said professor David Lidzey of the University of Sheffield. “We have shown that it can also be used to make solar cells using specially designed plastic semiconductors. Maybe in the future, surfaces on buildings and even car roofs will routinely generate electricity with these materials.” An artist’s impression of the University of Sheffield technique of spray coating glass with the polymer to create a solar cell. Courtesy of the University of Sheffield. Most solar cells are manufactured using energy-intensive tools and materials like silicon, which contain large amounts of embodied energy, whereas plastic requires much less energy to make. “The goal is to reduce the amount of energy and money required to make a solar cell,” Lidzey said. “This means that we need solar cell materials that have low embodied energy, but we also need manufacturing processes that are efficient, reliable and consume less energy.” By spray-coating a plastic layer in air, the team hopes the overall energy used to make a solar cell can be significantly reduced. Although their current devices are coated onto flat surfaces, the scientists say the method could also be applied to curved surfaces. The main restriction, however, is that such surfaces currently need to be very smooth. “We found that the performance of our spray-coated solar cells is the same as cells made with more traditional research methods, but which are impossible to scale in manufacturing,” Lidzey said. “We now do most of our research using spray coating.” A downside to using the plastic as solar cell materials is that they are not as efficient at generating electricity as silicon cells. The majority of solar panels found in the UK are made from silicon and are expected to last more than 25 years. It is unlikely that plastic cells will ever be this stable, but if the energy cost of such cells can be lowered enough, they will become more cost-effective than silicon cells over their life cycle. “Increasing the energy conversion efficiency and lifetime of plastic cells are significant issues that many groups are working on,” Lidzey said. “It should also be noted that the cost of silicon solar panels has reduced significantly over the last few years, so plastic solar cells will have to catch up with these improvements.” For more information, visit: www.shef.ac.uk/