* Flexible wire solar cells need less silicon
* Finding could lead to cheaper solar cells
By Julie Steenhuysen
CHICAGO, Feb 14 U.S. researchers have devised a
way to make flexible solar cells with silicon wires that use
just 1 percent of the material needed to make conventional
The eventual hope is to make thin, light solar cells that
could be incorporated into clothing, for instance but the
immediate benefit is cheaper and easier-to-install solar
panels, the researchers said.
The new material, reported on Sunday in Nature Materials,
uses conventional silicon configured into micron-sized wires (a
micron is one-millionth of a meter) instead of brittle wafers
and encases them in a flexible polymer that can be rolled or
"The idea is it would be lower cost and easier to work with
by being more flexible than conventional silicon solar cells,"
Michael Kelzenberg of the California Institute of Technology in
Pasadena, who worked on the study, said in a telephone
Solar cells, which convert solar energy into electricity,
are in high demand because of higher oil prices and concerns
over climate change.
Many companies, including Japanese consumer electronics
maker Sharp Corp (6753.T) and Germany's Q-Cells SE QCEG.DE,
are making thin-film solar cells using organic materials such
as polymers, but they typically are less efficient at
converting solar energy into electricity than conventional
cells using silicon.
The study is among the latest to combine the flexibility of
the new organic or carbon-containing films with the high
efficiency of silicon, which is heavy and stiff.
Kelzenberg said the material uses about 1/100th as much
silicon per cell area as a silicon wafer.
"It is potentially a route to bypass many of the costs
associated with producing solar cells," he said.
He said a big problem with working with silicon wafers is
they are fragile.
More testing is needed but Kelzenberg said the material
would be about 15 percent to 20 percent efficient, about the
same level as solar cells used on roofs to heat homes.
A similar effort is under way in the lab of John Rogers, a
professor of materials science at the University of
Illinois-Urbana-Campaign, who is working on ways to make
inorganic materials more flexible.
While many companies are investing in organic solar cells
-- basically materials like plastic that contain carbon --
Rogers said these materials have relatively low performance,
less long-term reliability and an unproven cost structure.
"We like the inorganics -- trying to adapt them and use
them in non-standard ways," Rogers said in a telephone
Last year, his team reported on a new manufacturing process
that creates thin arrays of solar cells that are flexible
enough to be rolled around a pencil and transparent enough to
be used to tint windows on buildings or cars.
"We can make them stretch like a rubber band or bendable
like a sheet of plastic," he said.
He is founder of a start-up semiconductor company called
Semprius Inc in Durham, North Carolina, that last month
announced a joint effort with Siemens AG (SIEGn.DE) to develop
large systems for utility-scale power generation.
"The same technology they are using to make these rigid
utility-scale modules could be used for flexible devices as
well," he said.
Rogers said that the company has funding from the U.S.
Department of Defense and the CIA.
(Editing by Maggie Fox and Bill Trott)