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Novel solar cells weather industry doldrums


GaAs photovoltaic developer, Semprius, looks set to shine in a solar market where so many are fading, reports Compound Semiconductor.


AFTER YEARS OF DEVELOPMENT, the concentrated solar power sector finally looks set to take off. Middle East governments recently pledged to spend tens of billions of dollars on large-scale plant at the United Nations Climate Change conference, validating analysts’ forecasts of healthy growth.


But just as the market looks promising, the CPV companies are floundering. California-based market leader Amonix recently closed its Nevada manufacturing site, swiftly followed by the demise of Greenvolts, also based in California. And then a few weeks later, San Jose-based SolFocus announced plans to sell, dismissing half of its staff, some 35 employees.


North Carolina-based CPV manufacturer, Semprius, has bucked this trend. In September 2012, the firm opened its first manufacturing plant in North Carolina, employing 50 staff poised to produce some 6 MW of panel a year. And then in November, the company revealed that US-based Pratt & Whitney Rocketdyne is to install a 200 kW system comprising 2400 of its modules at the US Department of Defense Edwards Air Force Base, in the California south-west desert.


As Russ Kanjorski, Semprius’s vice president for business development, tells Compound Semiconductor: “This is the perfect location to test our technology for future applications... and is just one commercial-scale project we expect to do in 2013.”


So what’s its secret? On its website, the company claims to have combined very high module efficiencies – up to a dazzling 33.9 percent – with industry-standard, low-cost microelectronics manufacturing techniques. The company’s modules comprise hundreds of triple-junction GaAs solar cells mounted on an industry-standard backplane.


Measuring only 600 µm by 600 µm by 10 µm, each cell is minuscule compared to your standard centimetre-sized cell and is designed to convert a relatively wide part of the solar spectrum into electricity, compared to silicon.


Semprius modules use hundreds of GaAs solar cells with lenses to concentrate light,boosting the efficiency and making the exotic photovoltaic affordable


16 www.compoundsemiconductor.net January / February 2013


Kanjorski believes the company’s success is also down to the cell fabrication process, which allows repeated use of the GaAs wafer. Semprius co-founder John Rogers has pioneered a ‘micro-transfer printing’ technique in which a sacrificial layer is first grown on a GaAs wafer, followed by epitaxial growth of thousands of triple- junction cells. Then, in a massive parallel process, a rubber stamp selectively picks up and transfers an array of cells to an alumina


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