It seems that half the world’s R&D is involved in solar energy, which isn’t a bad thing considering the mess our reliance on traditional energy generation has got us into. Interestingly, engineers at Princeton University have developed a new technique for producing electricity-conducting plastics that could dramatically lower the cost of manufacturing solar panels, making alternative power within reach of more consumers and industry.

The Princeton researchers have successfully produced plastics that are translucent, malleable and able to conduct electricity, and are now looking at applications for the materials, most likely in a wide range of electrical devices.

They believe plastics could represent a low-cost alternative to indium tin oxide (ITO), an expensive conducting material currently used in solar panels.

"Conductive polymers [plastics] have been around for a long time, but processing them to make something useful degraded their ability to conduct electricity," said Yueh-Lin Loo, an associate professor of chemical engineering, who led the Princeton team. "We have figured out how to avoid this trade-off. We can shape the plastics into a useful form while maintaining high conductivity."

Known as "organic electronics" because plastics are carbon-based like living creatures, the research could lead to new types of electronic devices and new ways of manufacturing existing technologies, because in the past the mysterious loss of conductivity has hampered production of moldable plastics.

"People didn't understand what was happening," said Loo, who co-wrote the research paper. "We discovered that in making the polymers moldable, their structures are trapped in a rigid form, which prevented electrical current from traveling through them."

By treating plastics with an acid after they were process in their new form, Loo and her colleagues have developed a way to relax the structure and keep the conductivity.

They have made a plastic transistor - a fundamental component of electronics that is used to amplify and switch electronic signals. They produced the electrodes of the transistor by printing the plastic onto a surface, a fast and cheap method similar to the way an ink-jet printer produces a pattern on a piece of paper. Gizmag has constantly reported on ink-jet technologies like those used to create solar cells.

Loo said the technique potentially could be scaled up for mass production presses akin to those used to print newspapers. "Being able to essentially paint on electronics is a big deal," Loo said. "You could distribute the plastics in cartridges the way printer ink is sold, and you wouldn't need exotic machines to print the patterns."

Solar cost-savings

By manufacturing solar cells using low-cost printing techniques and by replacing ITO as the primary conducting material, it’s easy to see why the team is excited about the potential for lower cost solar panels.

Currently, the electricity generated by plastic solar cells is collected by a transparent metal conductor made of ITO, a rare and expensive by-product of mining, which is also used in flat-screen TVs, mobile phones and other devices that use display screens. In order for the technology to work, the conductor must be transparent so that sunlight can pass through it to the materials in solar cells that absorb the light energy.

"The cost of indium tin oxide is skyrocketing," Loo said. "To bring down the costs of plastic solar cells, we need to find a replacement for ITO. Our conducting plastics allow sunlight to pass through them, making them a viable alternative."

Other purposes

Scientists are exploring the use of the plastics in biomedical sensors that would display a certain color if a person had an infection. For instance, the plastics turn from yellow to green when exposed to nitric oxide, a chemical compound produced during ear infections in children. These could provide valuable yet inexpensive medicinal benefits in third world countries.

"You wouldn't need any fancy machines or lab equipment to diagnose an infection," Loo said, "all you would need is your eyes to see the color change in the plastics."

A multi-institutional team reported the new technique in n online paper published recently in the Proceedings of the National Academy of Sciences.

The research was supported by the National Science Foundation, the W.M. Keck Foundation and the Arnold and Mabel Beckman Foundation.

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