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HelioVolt Corp of Austin, TX, USA, which makes thin-film copper indium gallium selenide (CIGS) solar cells and modules, said that its proprietary FASST reactive transfer printing process has produced uniform thin-film solar cells with a high conversion efficiency of 12.2% in a record-setting throughput of just 6 minutes (as confirmed by independent testing at Colorado State University). HelioVolt’s 12.2% efficiency came from a “champion cell” consisting of a CIGS thin-film layer applied to a glass substrate.

The results were reported by founder and CEO Dr BJ Stanbery during his keynote address ‘Entrepreneurship on the Road from Science to Sales’ at this week’s 33rd IEEE Photovoltaic Specialists Conference in San Diego, CA, USA.

Thin-film technologies aim to lower the cost of photovoltaic (PV) products by reducing the amount of material required compared silicon solar cells. FASST reduces costs further by manufacturing CIGS thin-film products 10-100 times more rapidly than competing processes including co-evaporation and two-stage selenization, the firm claims.

“In the lab, CIGS is already achieving the highest efficiencies of any thin-film solar material,” says Stanbery. Cadmium telluride (CdTe) PV cells – such as those produced by First Solar (the world’s biggest thin-film PV maker) - have achieved a record efficiency of about 16.5% in the labs (and an average of 10.6% in production). But in March the US National Renewable Energy Laboratories (NREL) reported 19.9% efficiency for a CIGS solar cell. However, NREL uses a co-evaporation process (where active chemicals are immersed in a solution, which then gets removed), which can take 40-50 minutes, according to HelioVolt.

“The challenge of course is transferring that efficiency to a high-throughput, high-yield, low-cost process capable of delivering gigawatts worth of quality commercial product,” Stanbery adds. “We view these high-performance results as an indicator of FASST’s potential to meet that need,” he adds. “We’re already producing CIGS devices that are comparable with the highest-efficiency thin-film products on the market today, and we still see plenty of room to improve from here.” For example, Miasolé (which plans to expand its capacity from 40MW to 100MW next year) claims that its CIGS panels have efficiencies of 9-10%. Nanosolar claims an efficiency of 9-10% for its commercial CIGS PV products, which started shipping at the end of 2007. In January CIGS PV maker Global Solar Energy (which, like NREL, also uses co-evaporation, and opened a 40MW CIGS manufacturing plant in March) exceeded 10% with its commercial products, and expects to hit 13-14% this year. Commercial silicon cells have efficiencies of 14-20%.

Last October, HelioVolt raised $101m in a Series B funding round involving venture financing. The firm is using the funds to optimize FASST for further efficiency gains and to scale up the process into volume production at its first $80m, 20MW commercial manufacturing line, as well as pursuing international expansion goals. VP of marketing John Langdon says that, when HelioVolt first delivers product in late 2008 or early 2009, efficiency should be 10-12%, but 12-15% should be commercially viable later.

The FASST process can also be used to print high-efficiency, low-cost thin-film material directly on glass substrates for solar modules or onto building products including architectural glass and roofing tiles. The firm initially plans to put the thin-film photovoltaic cells onto a glass substrate for solar panels, but later intends to put the flexible cells onto a plastic substrate so that they can be integrated into building materials in the form of building-integrated photovoltaic (BIPV) products.

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