A new technique developed by Princeton University engineers for
producing electricity-conducting plastics could dramatically lower
the cost of manufacturing solar panels.
By overcoming technical hurdles to producing plastics that are
translucent, malleable and able to conduct electricity, the
researchers have opened the door to broader use of the materials in
a wide range of electrical devices.
With mounting concerns about global warming and energy demand,
plastics could represent a low-cost alternative to indium tin oxide
(ITO), an expensive conducting material currently used in solar
panels, according to the researchers.
"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."
A multi-institutional team reported on its new technique in a
paper published online March 8 in the Proceedings of the
National Academy of Sciences.
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.
"People didn't understand what was happening," said Loo, who
co-wrote the 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."
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, a fast and cheap
method similar to the way an ink-jet printer produces a pattern on
a piece of paper.
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."
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 and pricey 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. 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.
If the devices could be produced at a low cost, they might be
useful in developing countries that lack advanced medical
facilities. "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."
SOURCE
