A new flexible film made of copper nanowires and plastic conducts electricity illuminating a small light bulb. Image: Ben Wiley, Duke University. |
Copper nanowires may be coming to a little screen near
you.
These new nanostructures have the potential to drive down
the costs of displaying information on cell phones, e-readers, and iPads, and
they could also help engineers build foldable electronics and improved solar
cells, according to new research.
Duke University chemist Ben Wiley
and his graduate student have developed a technique to organize copper atoms in
water to form long, thin, non-clumped nanowires. The nanowires are then
transformed into transparent, conductive films and coated onto glass or
plastic.
The new research shows that the copper nanowire films
have the same properties as those currently used in electronic devices and
solar cells, but are less expensive to manufacture. The results were published
in Advanced Materials.
The films that currently connect pixels in electronic
screens are made of indium tin oxide, or ITO. It is highly transparent, which
transmits the information well. But the ITO film must be deposited from a vapor
in a process that is a thousand times slower than newspaper printing, and, once
the ITO is in the device, it cracks easily. Indium is also an expensive rare
earth element, costing as much as $800/kg.
These problems have driven worldwide efforts to find less
expensive materials that can be coated or printed like ink at much faster
speeds to make low-cost, transparent conducting films, Wiley says.
One alternative to an ITO film is to use inks containing
silver nanowires. The first cell phone with a screen made from silver nanowires
will be on the market this year. But silver, like indium, is still relatively expensive
at $1400/kg.
Copper, on the other hand, is a thousand times more
abundant than indium or silver, and about 100 times less expensive, costing
only $9/kg.
In 2010, Wiley and his graduate student Aaron Rathmell
showed that it was possible to form a layer of copper nanowires on glass to
make a transparent conducting film.
But at that time, the performance of the film was not
good enough for practical applications because the wires clumped together. The
new way of growing the copper nanowires and coating them on glass surfaces
eliminates the clumping problem, Wiley says.
He and Rathmell also created the new copper nanowires to
maintain their conductivity and form when bent back and forth 1,000 times. In
contrast, ITO films’ conduction and structure break after a few bends.
Wiley said the low-cost, high-performance, and flexibility
of copper nanowires make them a natural choice for use in the next generation
of displays and solar cells. He co-founded a company called NanoForge Corp in
2010 to manufacture copper nanowires for commercial applications.
In early 2011, NanoForge received a $45,000 North
Carolina IDEA grant for refinement and scale-up of the manufacturing process of
copper nanowires, and it is now filling orders.
With continuing development, copper nanowires could be in
screens and solar cells in the next few years, which could lead to lighter and
more reliable displays and also to making solar energy more competitive with
fossil fuels, Wiley says.
