Scientists develop solar cells with a twist

CHICAGO, US: U.S. researchers have found a way to
make efficient silicon-based 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.

The finding, reported on Sunday in the
journal Nature Materials, offers a new way to process conventional
silicon by slicing the brittle wafers into ultrathin bits and
carefully transferring them onto a flexible surface.

"We can make it thin enough that we
can put it on plastic to make a rollable system. You can make it gray
in the form of a film that could be added to architectural glass,"
said John Rogers of the University of Illinois at Urbana-Champaign,
who led the research.

"It opens up spaces
on the fronts of buildings as opportunities for solar energy,"
Rogers said in a telephone interview.

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 and Germany's Q-Cells are
making thin-film solar cells, but they typically are less efficient
at converting solar energy into electricity than conventional cells.

Rogers said his technology uses
conventional single crystal silicon. "It's robust. It's highly
efficient. But in its current form, it's rigid and fragile," he
said.

Rogers' team uses a special etching method
that slices chips off the surface of a bulk silicon wafer. The sliced
chips are 10 to 100 times thinner than the wafer, and the size can be
adapted to the application.

Once
sliced, a device picks up the bits of silicon chips "like a
rubber stamp" and transfers them to a new surface material,
Rogers said.

"These silicon solar cells become
like a solid ink pad for that rubber stamp. The surface of the wafers
after we've done this slicing become almost like an inking pad,"
he said.

"We just print them down onto a
target surface."

The final step is to electrically connect
these cells to get power out of them, he said.

Adding flexibility to the material would
make the cells far easier to transport. Rogers envisions the material
being "rolled up like a carpet and thrown on the truck."

He said the technology has been licensed
to a startup company called Semprius Inc in Durham, North Carolina,
which is in talks to license the technology.

"It's just a way to use thing we
already know well," Rogers said.

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