Princeton Research Boosts Printing of Conductive Plastics

Conductive plastics can be printed on membranes to createsolar cells in a new technology developed by Princeton researchers with a NationalScience Foundation grant.

"Conductive polymers have been around for a longtime, but processing them to make something useful degraded their ability toconduct electricity," says Yueh-Lin Loo, an associate professor ofchemical engineering at Princeton. "We have figured out how to avoid thistrade-off. We can shape the plastics into a useful form while maintaining highconductivity."

The Princeton researchers treat the polymers with an acidto relax them following processing. Electrodes of a transistor were produced byprinting treated conductive plastic onto a surface.

"Being able to essentially paint on electronics is abig deal," Loo says. "You could distribute the plastics in cartridgesthe way printer ink is sold and you wouldn't need exotic machines to print thepatterns."

This method could be used to replace indium tin oxide(ITO), a conducting material often used in solar panels. The conductivematerial is transparent to allow sunlight to pass through to the materials insolar cells that absorb light energy.

There are some limiting factors with ITO. For one, highconcentration of charge carriers will increase ITO's conductivity, but decreaseits transparency. Another issue is that ITO has been in strong demand forcompeting applications, including liquid crystal displays, flat panel displays,plasma displays, touch panels, electronic ink applications, organiclight-emitting diodes, antistatic coatings and EMI shielding. ITO is used asthe anode in organic light-emitting diodes.

BiomedicalSensors

Loo says the treated conductive plastics may also be usedfor flexible displays and biomedical sensors that would display a certain colorif a person had an infection. The plastics change color when exposed to achemical compound common in ear infections.

Other researchers include Joung Eun Yoo, who received herdoctorate in chemical engineering from the University of Texas-Austin in 2009with Loo as her adviser; Kimberly Baldwin, a high school student who spent asummer in Loo's lab; Jacob Tarver, a Princeton chemical engineering graduatestudent; Enrique Gomez of Penn State University; Kwang Seok Lee and YangmingSun of the University of Texas-Austin; Andres Garcia and Thuc-Quyen Nguyen ofthe University of California-Santa Barbara; and Hong Meng of DuPont CentralResearch and Development.

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

Use of conductive plastics in solar cells is not new. Design News has previously reported oncommercial projects under way at Konarka andPlextronics. ThePrinceton research could presumably improve the economics for conductiveplastics in solar applications.

In the 1970s, Alan J. Heeger, Alan MacDiarmid and HidekiShirakawa reported high conductivity in oxidized iodine-doped polyacetylene inresearch that earned them the 2000 Nobel Prize in Chemistry "for thediscovery and development of conductive polymers." They were part of alarge effort dating back to the 1950s that had explored conductive polymers.

Today a trade group called the OrganicElectronics Assn. actively promotes commercial applications ofconductive polymers.

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