After introducing what appears to be a universal technique to reduce the work function of a conductor in printable electronics, a team led by Georgia Tech’s Bernard Kippelen has developed the first completely plastic solar cell. Photo: Georgia Institute of Technology |
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 cell phones.
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 televisions, for example, must be
covered with a rigid, thick barrier such as glass or expensive encapsulation
layers.
However, in new findings published in Science,
Georgia Institute of Technology 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 nm 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.”
