Printable Flexible Electronics Just Became
Easier With Stable Electrodes.
Imagine
owning a television with the thickness and weight of a sheet of paper. It will
be possible, someday, thanks to the growing industry of printed electronics.
The process, which allows manufacturers to literally print or roll materials
onto surfaces to produce an electronically functional device, is already used
in organic solar cells and organic light-emitting diodes (OLEDs) that form the
displays of cellphones.
Although
this emerging technology is expected to grow by tens of billions of dollars
over the next 10 years, one challenge is in manufacturing at low cost in
ambient conditions. In order to create light or energy by injecting or
collecting electrons, printed electronics require conductors, usually calcium,
magnesium or lithium, with a low-work function.
These
metals are chemically very reactive. They oxidize and stop working if exposed
to oxygen and moisture. This is why electronics in solar cells and TVs, for
example, must be covered with a rigid, thick barrier such as glass or expensive
encapsulation layers.
However,
in new findings published in the journal Science, Georgia Tech researchers have
introduced what appears to be a universal technique to reduce the work function
of a conductor. They spread a very thin layer of a polymer, approximately one
to 10 nanometers thick, on the conductor's surface to create a strong surface
dipole. The interaction turns air-stable conductors into efficient, low-work
function electrodes.
The
commercially available polymers can be easily processed from dilute solutions
in solvents such as water and methoxyethanol.
"These
polymers are inexpensive, environmentally friendly and compatible with existent
roll-to-roll mass production techniques," said Bernard Kippelen, director
of Georgia Tech's Center for Organic Photonics and Electronics (COPE).
"Replacing the reactive metals with stable conductors, including
conducting polymers, completely changes the requirements of how electronics are
manufactured and protected.
Their
use can pave the way for lower cost and more flexible devices."
To
illustrate the new method, Kippelen and his peers evaluated the polymers'
performance in organic thin-film transistors and OLEDs. They've also built a
prototype: the first-ever, completely plastic solar cell.
"The
polymer modifier reduces the work function in a wide range of conductors,
including silver, gold and aluminum," noted Seth Marder, associate
director of COPE and professor in the School of Chemistry and Biochemistry.
"The process is also effective in transparent metal-oxides and
graphene."
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