In the plastic transistor pictured here, the plastic is molded into interdigitated electrodes (orange) allowing current flow to and from the active channel (green). (Princeton University/Loo Research Group)
Princeton University engineers have developed translucent, malleable, and electricity-conducting plastics, which 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. “We have figured out how to avoid this trade-off. We can shape the plastics into a useful form while maintaining high conductivity.”

The area of research, known as "organic electronics" because plastics are carbon-based like living creatures, holds promise for producing new types of electronic devices and new ways of manufacturing existing technologies, but has been hampered by the mysterious loss of conductivity associated with moldable plastics.

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

Once they understood the underlying problem, Loo and her colleagues 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, 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.

“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.”

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 developed hold potential for lowering the cost of solar panels.

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.

A rare byproduct of mining, 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.