Monday, October 6, 2008

Semprius stamping out thin-film solar


For researchers at the University of Illinois, the key to a good solar panel is all in how you slice the silicon. John Rogers and his team of researchers at the University of Illinois at Urbana-Champaign have figured out how to slice monocrystalline solar wafers thin enough to be flexible and partially transparent but still maintain their high solar efficiency. The findings were published this weekend in Nature Materials. The slender silicon slices are then imprinted onto a substrate using Rogers’ patented microtransfer printing process, the technological process that is the basis for his startup Semprius.

Durham, N.C.-based Semprius, founded in 2005, is working on applying that microtransfer printing process to the manufacture of a number of electronics including LCDs, OLEDs, radio devices and large sensors. The company has also been developing a multijunction gallium arsenide cell for a concentrator module for the past year and a half, Semprius’s VP of Photovoltaics, Bob Connor, tells Earth2Tech. The company’s patent portfolio, as licensed from the University of Illinois, does include the possible use of monocrystalline silicon, but Rogers tells us that there are no immediate plans to commercialize his research in silicon. However, Rogers says he has already seen interest from larger solar players, and Semprius could license the monocrystalline silicon application to a third-party developer.

The potential of monocrystalline silicon being used in thin-film solar is exciting because until now it has always come in relatively thick, brittle wafers that were inflexible and expensive. That’s why thin film startups have been looking to other materials for photovoltaics. Nanosolar is working with copper indium gallium selenide (CIGS), First Solar has succeeded with cadmium telluride and OptiSolar is looking to scale amorphous silicon, monocrystalline silicon’s less-efficient but more malleable cousin.

However, while commercial monocrystalline silicon cells can top 20 percent solar efficiency, thin-film solar players are often struggling to reach 10 percent. John Rogers says that his team’s cells can hit 12 percent efficiency, and they’re still in the lab. With silicon prices coming down, microtransfer printing could be the key to cheap, mass producible silicon-based thin-film solar.

The key to the microtransfer printing technology is that it fundamentally separates semiconductor fabrication from the fragile substrate. After the “hot” process of semicom fab, a stamp picks up tens of thousands of cells at once and “prints” them onto a “cool” substrate, either flexible plastic or architectural glass. The result is a highly efficient, highly flexible solar cell that the researchers claim will be cheaper than existing silicon cells.

The company raised $4.7 million in Series A funding in April of 2007 from from Arch Venture Partners, Intersouth Partners and Illinois Ventures. In July of that same year, Applied Ventures joined with an undisclosed strategic investment in the solar startup. Connor says the company is currently seeking a new round of funding.

Images courtesy of Semprius and John Rogers.

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