O-L-E-D us to salvation!

New plastics could give us light and harvest it too.

Neil Owens

Imagine painting your wall and then plugging it in so that it changed colour every day. The same idea could be applied to clothing, which would undoubtedly draw attention from those in areas as far apart as fashion, the military and safety equipment. These ideas may not be as far-fetched as you might think, thanks to research into a new material called conducting polymers, some of which is being carried out here at the U of M.

Conducting polymers conduct electricity just like metal wires but are different because they are carbon-based. In fact, the name “conducting polymers” refers to a group of polymers with similar properties that are so new that they don’t yet have a catchy name. The hallmarks of conducting polymers are the abilities to be applied onto a surface in a very thin layer, such as by painting, and being extremely energy efficient at producing light.

It has been known for several decades that some types of polymer can conduct electricity, but it’s only recently that they created a buzz when it was discovered they can produce light. “What really created excitement was the discovery of OLED’s (organic light emitting diodes),” said Michael Freund, a Canada Research Chair in Conducting Polymers and Electronic Materials and professor of chemistry at the University of Manitoba. He explained how OLEDs are now being sold as an improvement over liquid crystal displays (LCDs), which basically filter out most of the light produced. “[With LCDs], it’s an extremely inefficient process: you make a lot of light with all wavelengths and then you get rid of most of it just to have one colour.”

This has spurred interest in the next generation of display technology for cellphones, cameras, MP3 players and eventually televisions and computers, “Sony, Kodak, Philips; all the major companies are developing [OLEDs] because they are so thin and so energy efficient.”

This kind of material could also be used to transport electricity over long distances, but Freund explained that research into conducting polymers is not aimed at just getting highly conductive materials, “There have been a few reports of conducting polymers that do conduct electricity as well as copper, but they’re not common at all. There’s no reason to try to beat copper in terms of conductivity.”

What makes conducting polymers special and in a different class from metals and even semiconductors like silicon, is that they can change their electrical output in response to changes in their environment, as explained by Freund: “The idea is making an active material, a material whose properties change depending on the oxidation state or doping state; if the environment changes that, then you can measure it electrically.” This lends conducting polymers towards more specialized applications: new kinds of transistors, memory storage, batteries, and devices that can “sense” changes in their environment.

Some limitations still exist; one is that the polymers degrade over time. “There have always been some limitations because organic compounds biodegrade. The creation of these charge carriers makes a polymer that is not inherently stable. People have been working on that, trying to make them less reactive, and there’s been a lot of success from that,” Freund explained. Another problem being worked on arises from the fact that the polymers do not easily dissolve in liquids, which limits their use.

“Typically the polymers are very insoluble, which can be good for certain things. But if you want to paint it on the wall, then you can’t even get it into a suspension,” Freund explained. Freund has been working to solve this problem by painting on the required chemicals then letting polymerization happen in place. The potential payoff for solving the issues surrounding conducting polymers is huge, being no less than solving the world energy crisis.

The ability to cheaply harvest solar energy could be the biggest boon derived from conducting polymers. Some researchers are trying to use the titanium dioxide found in white paint as the basis for solar panels (Graetzel cells) that could literally be painted on any surface to collect solar radiation. Freund said, “If you do want to make (solar panels) cheap and paintable, conducting polymers would have to be incorporated somehow because you can’t paint copper or the typical metals. I know that there is a lot of work being done on incorporating conducting polymers into solar cell applications.” Freund continued to say that there still needs to be work done in this area, but the potential payoff is huge. “They, in theory, know how Graetzel cells work, but there’s still components of it that they can’t explain. I think if somebody makes a major breakthrough in understanding or development, then I think it will be really huge,” he declared.

Neil Owens is a PhD candidate student in chemistry at the University of Manitoba.