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Wakonda hopes to disrupt solar market with its high-efficiency thin-film PV on foil

30 June 2008 | By Tom Cheyney | Chip Shots

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Although there were plenty of "me-too" technologies discussed at the recent IntertechPira Photovoltaic Summit in San Diego, one start-up outfit's approach offers more disruptive potential than most thin-film PV wannabes. Wakonda Technologies, based in Fairport, NY (but soon moving to larger digs near Boston), has been working for about three years on an intriguing TFPV variant--high-efficiency germanium and gallium-arsenide-based cells made on a flexible metal-foil substrate which is potentially scaleable to high-volume roll-to-roll manufacturing.

Fritzemeier

Wakonda's Fritzemeier doesn't want "me-too" status.

President/CEO/founder Les Fritzemeier described a technology that combines the low materials and manufacturing costs of thin films, as well as much reduced systems and installation costs, with the high efficiencies of concentrating PV cells, producing significantly more power per unit area, per unit cost, and per unit weight. The key is what the company calls its "virtual single crystal" (VSC), which features a three-layer substrate with a low-cost, commodity metal base foil (this is the core tech, so its composition remains proprietary), an engineered buffer film, and a Ge growth layer on top, which also functions as the bottom cell layer. A III-V PV cell is then deposited on top of the stack.

In effect, the flexible, large-area substrate substitutes for single-crystal Ge or GaAs wafers. The processes are "relatively straightforward," according to Fritzemeier, and the goal is to process 25-inch-wide rolls of the metal foil, with several miles' worth on each roll. The company plans to leverage low-cost, roll-to-roll manufacturing, not in a continuous process sequence but more likely in a batch-serial approach, which is easier to calibrate on a factorywide level.

Prototype cell efficiencies of 5% were reached six months ago, but the company founder said the conversion number is moving quickly toward the goal of commercial efficiencies in the high-teens and twenties, like those for single-junction GaAs and multijunction III-V cells. In addition to the concentrating PV, aerospace/defense, and grid-tied market segments (what he called "the big play" in the long term) already targeted by the firm, the VSC substrate could have applications in the realms of hybrid organic/inorganic novel devices, flexible display and lighting, quantum dot enhancement, and a range of bandgap-engineered films.

One key to Wakonda's strategy is the use of already existing commercial infrastructure in the areas of materials, high-rate processing, and industrial-scale equipment. Because the technology is still at an early stage, Fritzemeier said the process that wins out could be vacuum or nonvacuum (or a hybrid of both), including even inkjet-printing wet solution approaches. But for now, the focus will be on R2R PVD for the most part, he added.

What's next for Wakonda? Although he wouldn't offer a prediction on when modules incorporating the company's cells would be on the market, Fritzemeier told the audience that they are in the midst of transitioning from small lab-scale efforts to their initial R2R pilot line over the next several months. When asked how the metal substrate will be interconnected to the rest of the device, he said there are several options, including monolithic or dielectric approaches, using (or not using) laser scribes.

He also said that the company who supplies the magic metal foil has plenty on hand for now--about 100 MW of capacity already in place--by in the longer term, other companies could be "taught" to do the manufacturing, when the time comes for securing a second or third source for the material.

Already the beneficiary of NREL's Clean Energy Entrepreneur of the Year award in 2007 and some $893,000 from the Department of Energy's next-gen solar energy program (as part of a $2.1 million project), Wakonda and its nascent breakthrough, which can take advantage of III-V level conversion efficiencies on a flexible substrate while keeping materials and manufacturing costs low, have staked a legitimate claim to the upper tier of the emerging PV technologies watchlist.

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