Professors Cor Koning (left) and Paul van der Schoot
(right), with their new transparent conducting film (Image: Bart
van Overbeeke)
With its two chief properties of excellent electrical
conductivity and optical transparency, indium tin oxide (ITO)
can be found in transparent conductive coatings for displays
found in all kinds of products, such as TVs, mobile phones and
laptops, and is also used as a transparent electrode in
thin-film solar cells. Unfortunately indium is a rare metal and
available supplies could run out in as little as ten years. This
has prompted researchers to search for alternatives with some
success already reported using
carbon nanotubes and
copper nanowires. The latest ITO replacement material also
uses carbon nanotubes, as well as other commonly available
materials, and is environmentally friendly.
The replacement material developed by researchers at
Eindhoven University of Technology is a transparent, conducting
film that is produced in water using carbon nanotubes and
plastic nanoparticles. The researchers start by dissolving
standard, widely available carbon nanotubes in water. They then
add conducting latex, which is a solution of polymer beads in
water, and a binder in the form of polystyrene beads. Upon
heating, the polystyrene beads fuse together to form the film,
which contains a conducting network of nanotubes and beads from
the conducting latex. The water is then removed by freeze-drying
leaving the transparent, conductive film.
Because high concentrations of carbon nanotubes would make
the film black and opaque, the researchers have kept the
concentration as low as possible, with the nanotubes and the
conducting latex together accounting for less than one percent
of the weight of the film.
While the conductivity of the film is still a factor 100
lower than that of ITO, the researchers say it is already good
enough to be used as an antistatic layer for displays, or for
EMI shielding to protect against electromagnetic radiation. The
researchers also expect the gap in electrical conductivity
between their film and ITO to be quickly closed.
"We used standard carbon nanotubes, a mixture of metallic
conducting and semiconducting tubes", says Cor Koning. "But as
soon as you start to use 100 percent metallic tubes, the
conductivity increases greatly. The production technology for
100 percent metallic tubes has just been developed, and we
expect the price to fall rapidly."
Another advantage the new film has over ITO is that it is
environmentally friendly. All the materials used to produce it
are water based and, unlike ITO, no heavy metals are used. The
film is also more suited to flexible displays than ITO layers,
which are fragile and lack flexibility.
The Eindhoven
University of Technology (TU/e, Netherlands) research team
was led by theoretical physicist Paul van der Schoot and polymer
chemist Cor Koning. Post-doc Andriy Kyrylyuk is the first author
of the paper detailing the new film, which appears in
Nature
Nanotechnology.
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