Special Reports
See-Through, Bendable Solar Cells Could Expand Use of Solar Power

By Joyce Gramza
November 7, 2008

Solar power cells are still flat, rigid and ugly, 50 years in the making, but
that’s about to change, based on new research. Not only might cells be more
lightweight, flexible and transparent, their uses could be expanded to things
like solar fabrics or power-generating windows. This ScienCentral News video
explains what this research means for the future of solar power cells.

Up until now solar panels have had their fair share of limitations, being heavy,
rigid and fragile. But John Rogers, a professor at the University of Illinois
Urbana-Champaign, and his team of researchers have created a method to produce
extremely thin solar cells that can also be transparent and flexible.

“If you look at a conventional solar panel, it’s relatively heavy, mechanically
rigid, it’s fragile, you can’t bend it, it’s opaque, you can’t see through it,”
Rogers explains. “Our work here is to address those limitations.”

No one has found a more desirable material than silicon for generating solar
power, but Rogers and his team invented a way to use extremely thin slices of
the material.

"The way solar cells are currently manufactured with silicon demand that
thickness to achieve sufficient resistance to fracture so that they can make the
solar cells at high yields," Rogers explains.

He and his team showed that thickness is not necessary to make silicon solar
cells efficient at producing power from the sun. They figured out how to create
silicon solar cells that are 100 times thinner than conventional solar cells. To
achieve the best possible performance, Rogers’ team uses a monocrystalline
variety of silicon. And they invented a process for using the ultra-thin cells
to design solar modules without damaging them. The process is similar to a print
process, which transfers the slices onto lightweight plastic or fabric.
This method allows photovoltaic cells, the building blocks of solar panels, to
be more efficient and potentially less costly.

“So we have thin, lightweight, mechanically bendable and even partially
transparent module designs that we think could potentially open up new areas of
application for silicon-based solar technology," Rogers says.

Recycle, Reduce, Reuse

Because the new, thin modules use much less material, the researchers can create
more solar cells from the same silicon “wafer.”

“We work our way through the entire thickness of the wafer, thereby making very
efficient use of the silicon material in the solar cell technology that we
developed,” Rogers says.

But this extreme thinness requires a support system to prevent breakage.
“These are extremely thin solar cells — about one tenth the thickness of a human
hair — so without that support structure they can be easily broken,” he
explains. “The purpose of the plastic substrate is just to form a mechanism
support so that your solar cell is robust and not prone to fracture or failure.”

A Bright Future

According to Rogers and his researchers’ report in the journal, “Nature
Materials,” their tests showed that the ultra-thin cells are just as efficient
as the conventional cells, while using much less material. Rogers says their
flexibility and transparency will open the doors to more solar power

“You could roll them up, throw them in the back of a truck like a carpet, and
then unfurl them when you’re installing them in their final location,” Rogers
says. "Those kinds of things are very difficult to do when your solar cell
technology is rigid and bulky and heavy."

And by adjusting the density of the cells on the module designs, the researchers
can give them different degrees of transparency or opacity. They could be used
as lamination on the outside of a building, on power-generating windows, or on
the tinted sunroof of a car, Rogers explains.

“You can imagine putting solar cells in all kinds of places that previously were
extremely difficult to do,” he says. "You can imagine integrating these things
with clothing, or the surfaces of tents or backpacks."

Those applications "could be possible with other kinds of flexible solar cells,
but they have their own disadvantages in terms of performance and reliability.
So it’s really bringing the well-developed silicon technology to this world of
flexible solar cells to enable these new possibilities,” he says.

Indeed, some of those applications are now available using other materials, but
Rogers writes that there’s good reason why silicon "is used in more than 90% of
all installed photovoltaic capacity… "If one considers a metric that integrates,
cost, materials abundancy, efficiency and lifetime, by this measure, silicon is
the best."

Rogers has confidence that this new method of creating solar panels will not
only be efficient and attractive, but there’s a good chance it will reduce the
cost of solar energy, making it a more affordable energy option for the future.
The University of Illinois has filed patents on the new inventions, and a North
Carolina company called Semprius has licensed the technology.

“We’re pretty optimistic that the kinds of approaches we’re developing now could
have real commercial potential and could be valuable as an alternative way to
generate industry,” Rogers says.

National Science Foundation Solar Energy Initiative
Solar Timeline from US DOE
International Solar Energy Society


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