A new wire twist on silicon solar cells

CHICAGO--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 solar cells.

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 bent.

"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 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 and Germany's Q-Cells SE, 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 nonstandard ways," Rogers said in a telephone interview.

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 in Durham, N.C., that last month announced a joint effort with Siemens 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.
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