By overcoming technical hurdles to producing plastics that are translucent, malleable and able to conduct electricity, the researchers claim they have opened the door to broader use of the materials in a wide range of electrical devices.

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

"Conductive polymers 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."

"We discovered that in making the polymers moldable, their structures are trapped in a rigid form, which prevented electrical current from traveling through them."

Once they understood the underlying problem, the researchers developed a way to relax the structure of the plastics by treating them with an acid after they were processed into the desired form.

Using the method, they were able to make a plastic transistor. 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.

By allowing plastic solar cells to be manufactured using low-cost printing techniques and by replacing ITO as the primary conducting material, the plastics the team have developed hold the potential for lowering solar panel costs.

Currently, the electricity generated by plastic solar cells is collected by a transparent metal conductor made of ITO. The conductor must be transparent so that sunlight can pass through it to the materials in solar cells that absorb the light energy.

The price ITO had come under increasing demand for use in flat-screen televisions, mobile phones and other devices with display screens. "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."

The researchers anticipate that the plastics also could replace expensive metals used in other electronic devices, such as flexible displays. In addition, the scientists are beginning to explore 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.

A multi-institutional team reported on its new technique in a paper published online March 8, 2010 in the Proceedings of the National Academy of Sciences.

Related link: www.princeton.edu/engineering