Researchers in the UK have come up with a way to fabricate solar cells that involves a process similar to spray painting and lowers the price of manufacturing the cells, potentially making them more accessible.
Originally, the idea to apply an active polymer material to photovoltaic devices involved a process called spin-casting that is similar to how a potter's wheel works, David Lidzey, a professor in the University of Sheffield's Department of Physics and Astronomy and one of the leads on the project, told Design News. However, that method was not scalable to a large area, so -- inspired by project partners -- the research team last year devised a new way to apply the material via a spray-coater system that's similar to common spray painting. Lidzey told us:
The idea of using a spray-coater was suggested to us by a group of industrialists we were collaborating with. They pointed out that this technique is already used to put down other films at industrial scale, and would be very interesting to adapt to put down the active layer of organic photovoltaic devices.
The system works using a piezoelectric ceramic element that vibrates a high frequency, onto which a solution of semiconductor ink is fed onto the surface. The vibrations break the solution up into fine droplets that are then carried to the surface of a cell by a jet of nitrogen carrier gas. Lidzey said:
At present, most research groups around the world use spin-coating to deposit thin films for organic electronic applications. The spray-coat technique is, we feel, better than this as it is less wasteful of expensive organic semiconductor inks, and can in principle be scaled up to very large size -- something that would be difficult by spin-coating.
The benefit of this method is that spray-coating is a low-waste process already used widely in industries such as graphic arts and automotive to produce thin-film coatings. To apply this process to creating organic solar cells that use polymer rather than silicon as an active material -- a nascent but evolving industry -- could make the production of cells less expensive and also be applied to other fabrication processes.
Organic photovoltaics do however hold out significant promise as the technology requires a lower energy input compared to other solar cells -- e.g., crystalline silicon -- where expensive infrastructure and high temperature processes are often required. Organic materials require less energy input into their synthesis, and spray-coating is an energy-efficient manufacture process. This means that organic solar-cells may have much lower embodied energy than other solar-cell technologies.
There are some drawbacks to the organic cells, Lidzey pointed out, which currently have lower efficiency and much lower operational lifetimes. However, "these are issues that many groups around the world are currently addressing."
In addition to creating solar cells, the spray-coating method could also one day be used to apply a photovoltaic material to car roofs and glass windows, giving those surfaces the ability to store and generate energy, researchers said.
Lidzey and his team will continue to experiment with spray-coating to scale up the devices being fabricated, since they are currently on the small side. "We would also like to further improve device efficiency, and find ways of using spray-coating to control the nanostructure of the thin films and thereby make further gains in device efficiency," he said.
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