Hybrid Solar Cells Combine Nanotech with Plastics
Solar-cell tech turns to plastic power
Researchers developing flexible, cheap devices that use sun's energy
(Photo: Janke Dittmer, Wendy Huynh and Paul Alivisatos of the University of
California at Berkeley show off an experimental array of solar cells. An
electrical current is generated within a brownish-orangish film of plastic.)
By Alan Boyle
March 28, 2002 - Researchers are finding new ways to make solar power cells
out of plastic - creating electricity-generating materials you could print
on a sheet of paper, stick onto your windows, have painted on your house, or
even wear on your back. They say plastic power could go commercial in just a
Most people think of solar cells as the large arrays of dark, glassy squares
that provide electricity for the international space station, the Hubble
Space Telescope and earthbound solar-power pioneers trying to break their
reliance on the power grid. But when it comes to 21st-century photovoltaics,
the trend is heading toward a thinner, cheaper breed of solar cell.
The state of the art in solar power involves flexible thin-film sheets of
laminated semiconducting material that can convert 20 percent to 35 percent
of the sun's energy into electricity. The problem with thin-film cells is
that they're still relatively expensive to manufacture, requiring clean
rooms and vacuum chambers.
Several teams of researchers are trying a completely different approach,
using plastics spiked with exotic inorganic materials like buckyballs or
nanorods. Such materials could be mixed up like paint or ink, then sprayed
or silk-screened onto a surface in combination with flexible electrodes.
"We use a much dirtier process that makes it cheap," said A. Paul
Alivisatos, a chemistry professor at the University of California at
Berkeley and a researcher at Lawrence Berkeley National Laboratory.
One path of power
Alivisatos and two colleagues, Wendy Huynh and Janke Dittmer, describe the
process in Friday's issue of the journal Science. It's not yet ready for
prime time, since the solar cells achieved efficiencies of only 1.7 percent
and produced only about 0.7 volts of electricity. But the researchers
believe they're just beginning to follow a trail that could lead to the next
generation of portable power.
The Berkeley team created a blend of organic polymers and an assortment of
two types of nanorods - clusters of cadmium selenide molecules that looked
like grains of rice but measured only 7 or 60 nanometers in diameter. The
nanorods were designed so that they absorbed particular wavelengths of light
and converted them into electrical current. The key was the shape and
orientation of the nanorods, Alivisatos said.
"Because the electron mobilities are higher in the rods, we can make a lot
of improvement over time," he told MSNBC.com. "Usually, the efficiency will
end up being related to how good the mobility is in these materials."
That's what gives Alivisatos hope that the Berkeley breed of solar cells
will eventually approach the 10 percent efficiency level required for a
commercially viable product, by using a standard toolbox of engineering
Eventually, the material, which "looks like a tinted car window that has a
brownish-orangish tinge to it," could be sprayed onto glass, stuck on a
briefcase, even plastered onto clothes for wearable electronics, he said.
"I don't know if the color would look so great" for clothing, he joked. "It
may be a design feature."
Another team at the University of Arizona is using a similar approach to
plastic solar cells, employing carbon-based buckyballs - exotic molecules
that look like spherical cages - rather than the Berkeley team's nanorods.
Each team is familiar with the other's work. Alivisatos said his research
was following in the Arizona team's footsteps, while Ghassan Jabbour, an
optical sciences professor at Arizona, told MSNBC.com that Alivisatos' work
was "excellent ... it's another variation of doing photovoltaics."
"By no means is one approach better than the other," said Jabbour, whose
findings have been published in Applied Physics Letters. "The fact that none
of them has shown more than 5 percent efficiency shows that there is a lot
of work to be done."
Nevertheless, Jabbour is optimistic that he's also on the right trail. He
says his plastic solar cells have achieved efficiencies of more than 2
percent, and his team recently demonstrated an inkjet-printing system that
could spray a light-emitting layer onto an electrically conductive surface.
The experiment produced self-illuminated images, printed on plastic - but
the same principle could be applied someday to create electronic circuits on
paper, glass or clothing.
Such techniques could dramatically lower the cost of solar cells in the next
five years or so, Jabbour said.
"You can make them by the mile and sell them by the inch," he said.
Jabbour said the first applications would involve "short-term,
light-emitting devices or other types of microelectronics that would only
require very low power": for example, paper-thin disposable pagers, watches,
calculators, perhaps even a small, head-mounted computer.
But he also dreams of the day when curtains and wallpaper could be coated
with power-generating plastic.
"I would like to make a window or a curtain so that one side can be
photovoltaic and the other side is a light-emitter," he said. That way, the
tinted window could soak in the sunlight during the daytime, then light up
the room at night, he said.
"It's pretty exciting stuff we're doing here," Jabbour said.
© 2004 MSNBC Interactive
One potential product is a new type of solar cell that performs like a
traditional solar cell, but can be configured like a light weight, flexible
plastic. In particular, this technology has the potential to provide low
cost solar power through currently available, high volume and inexpensive
manufacturing techniques based on conventional film based processes such as
roll to roll manufacturing. To develop our nanotechnology-enabled solar
cells we are collaborating with Matsushita and several United States