As the market for liquid
crystal displays and other electronics continues to drive up the price of
indium -- the material used to make the indium tin oxide (ITO) transparent
electrodes in these devices -- scientists have been searching for a less costly
and more dynamic alternative, particularly for use in future flexible
electronics.
Besides its high price, ITO has
several drawbacks. It's brittle, making it impractical for use in flexible
displays and solar cells, and there is a lack of availability of indium, which
is found primarily in Asia . Further, the production of ITO films is relatively
inefficient.
Now, researchers at UCLA report
in the journal ACS Nano that
they have developed a unique method for producing transparent electrodes that
uses silver nanowires in combination with other nanomaterials. The new
electrodes are flexible and highly conductive and overcome the limitations
associated with ITO.
For some time, silver nanowire
(AgNW) networks have been seen as promising candidates to replace ITO because
they are flexible and each wire is highly conductive. But complicated
treatments have often been required to fuse crossed AgNWs to achieve low resistance
and good substrate adhesion. To address this, the UCLA researchers demonstrated
that by fusing AgNWs with metal-oxide nanoparticles and organic polymers, they
could efficiently produce highly transparent conductors.
The
team of researchers represents a collaboration between the department of
materials science and engineering at the UCLA Henry Samueli School of
Engineering and Applied Science; the department of chemistry and biochemistry
in the UCLA College of Letters and Science; and the California NanoSystems
Institute (CNSI) at UCLA.
The team was led by Yang Yang, a professor of
materials science and engineering, and Paul Weiss, director of the CNSI and a
professor of materials science and engineering and of chemistry and
biochemistry.
"In this work, we demonstrate a simple and
effective solution method to achieve highly conductive AgNW composite films
with excellent optical transparency and mechanical properties," said Yang
who also directs the Nano Renewable Energy Center
Scientists can easily spray a surface with the
nanowires to make a transparent mat, but the challenge is to make the silver
nanowires adhere to the surface more securely without the use of extreme
temperatures (200° C) or high pressures, steps that make the nanomaterials less
compatible with the sensitive organic materials typically used to make flexible
electronics.
To meet this challenge, Rui Zhu, the paper's
first author, developed a low-temperature method to make high-performance
transparent electrodes from silver nanowires using spray coating of a unique
combination of nanomaterials.
First, researchers sprayed a solution of
commercially available silver nanowires onto a surface. They then treated the
nanowires with a solution of titanium dioxide nanoparticles to create a hybrid
film. As the film dries, capillary forces pull the nanowires together, improving
the film's conductivity. The scientists then coated the film with a layer of
conductive polymer to increase the wires' adhesion to the surface.
The AgNW composite meshes are highly conductive,
with excellent optical transparency and mechanical properties. The research
team also built solar cells using the new electrodes and found that their
performance was comparable to that of solar cells made with indium tin oxide.
The research received support from the Office of
Naval Research and the Kavli Foundation.
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