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10 September 2009


Nanosolar opens 640MW CIGS PV panel assembly plant in Berlin

Nanosolar, the US-based manufacturer of CIGS (copper indium gallium diselenide) thin-film photovoltaic cells, says that it has begun volume production of panels based on its novel technology.

Having started cell production at its roll-to-roll printing facility in San Jose, CA earlier this year, Nanosolar's panel-assembly factory close to Berlin was inaugurated on 9 September.

Picture: A roll of CIGS foil in Nanosolar’s San Jose factory. One full roll is said to by the company to be capable of delivering a total power of 100kW.

According to the company, the factory in Luckenwalde will be capable of an annual production capacity of 640MW when fully utilized and operating around-the-clock.

Initial utilization rates will be significantly lower than that, however, with start-up production set at just 1MW per month, or less than 2% of maximum capacity.

“[Nanosolar] will increase its monthly production rate to deliver on its contractual customer commitments totaling $4.1bn to date,” the company said.

CEO Martin Roscheisen also revealed that Nanosolar’s best CIGS-on-aluminum cells had been measured to deliver a conversion efficiency of 16.4%, in tests carried out at the US National Renewable Energy Laboratory (NREL).

The tests, performed in April, showed that a best-in-class CdS/Cu(In,Ga)Se2 cell with an area of 0.5cm2 yielded a conversion efficiency of 15.3%. The higher figure quoted by Nanosolar refers only to the active area of the cell.

The results were revealed in a white paper published on Nanosolar's web site – although not in a peer-reviewed journal – and also showed that the median efficiency of its best in-production panels is 11.75%.

In the same white paper, Nanosolar revealed more about its production technology than has been released to date.

Having tried out a wide range of different techniques to deposit CIGS onto a conducting substrate, the company settled on a foil-lamination process. Instead of using a glass substrate, as has typically been the method of choice for CIGS cell makers, Nanosolar uses an aluminum foil. The other key difference is the thickness of some of the key layers of the cell. For example, Nanosolar's molybdenum layer, used as the bottom electrode in the material stack, is only 50nm thick. Its CIGS layer is (as is typical) about 1 micron thick.

“This new approach is particularly cost efficient,” claims the company in its paper. “Roll-to-roll lamination is a widely employed, simple, and very-high-throughput processing technique,” he adds. “It works specifically (and only) for thin-film solar cells based on high-conductivity foil.”

Crucially, says the company, the production of stoichiometric ratios of copper, indium, gallium and selenium has been addressed in a reproducible way.

Conventionally, high-vacuum processes common to semiconductor manufacturing, such as sputtering or evaporation techniques, have been used to deposit the active elements of the cell reliably. Nanosolar says that it is now able to do this using a wet printing process, without the need for cleanroom conditions.

“Our team has developed proprietary types of nanoparticles, [and] proprietary organic dispersion chemistry by which these nanoparticles can be dispersed into a readily printable ink,” claims the company, adding that a proprietary rapid thermal processing technology is able to convert the precursor layer into a high-quality, dense semiconductor film.

Nanosolar clearly believes that there is plenty of room to improve the technology further: “We believe we are only at the very beginning of the potential of our technology platform and see more opportunities than ever based on the manufacturing processing we have established.”

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The author Michael Hatcher is a freelance journalist based in Bristol, UK.