Solar short takes: Suniva implements ion implantation, First Solar turns knobs, CIGS gets purified

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Tom Cheyney
Tom Cheyney
Tom Cheyney, former senior editor of PV-Tech and Photovoltaics International, is now chief curator of SolarCurator.com and director of Impress Labs’ solar practice.

With the New Year gaining inexorable momentum and the Chinese Lunar Spring Festival right around the corner, it’s time for the first Solar Short Takes blog of 2011. This edition features news of U.S. cellmaker Suniva and its ground-breaking use of ion implantation in volume production of high-efficiency solar cells, a few tidbits about First Solar’s engineering focus areas and view of CIGS, an enabling material purification approach for CIGS, calls for papers from two of the leading PV conferences, and a few thoughts on a certain Korean-Chinese company’s (re)branding.

The recent crash and ongoing burn of cell maker SpectraWatt makes the success of Suniva, another Team Solar USA  player, all the more noteworthy. The company, which has three cell manufacturing lines running at max capacity near Atlanta and should soon announce its plans to expand production, has established itself not only as capable of competing with the Chinese and other global entities, but as a technology leader in the crystalline-silicon arena.

In a technical paper appearing exclusively in the latest issue of Photovoltaics International (our 10th edition!), Suniva reveals that it has introduced ion implantation into volume production of its high-efficiency solar cells—an industry first.  

“The technique offers several advantages over conventional POCl3 and in-line diffusion technologies, including single-side dopant incorporation; in-situ oxidation for superior surface passivation; elimination of the PSG removal step; elimination of the junction edge-isolation step; precise doping control and novel dopant profile engineering by varying implantation dose, implantation energy, and implant damage annealing recipe; and patterned dopant regions for selective emitter and possibly interdigitated back contact-type cell structures,” according to the paper.

Admittedly, attempts to incorporate ion implantation in cell processing are not new, but the technique never gained traction because of the perceived double-whammy of slow throughput and high cost. But as the paper points out, “interest in ion-implanted emitters has reawakened, with the potential of the implantation technique recognized as a way to produce advanced high-efficiency cell structures with fewer processing steps.”

Suniva has partnered with implant equipment aces Varian Semiconductor Equipment Associates, “which led the development of high beam current, fast wafer handling, high-throughput implanters specifically designed for the PV industry.”

More information about Varian’s ion implantation technology for PV manufacturing floors can be found here and here. I also encourage interested subscribers to read the article if they haven’t already; for subscribers and nonsubscribers alike, please go to this link and follow instructions for downloading the piece.   

No discussion of Team Solar USA would be complete without a mention of First Solar, the premiere purveyors of cadmium telluride thin-film modules as well as project development and engineering/ procurement/construction of large-scale PV farms. The company is notoriously tight-lipped when it comes to information about its R&D and production endeavors, but once in awhile a few tasty morsels make their way onto the blog buffet.

Raffi Garabedian, who directs First’s disruptive technology efforts at its skunkworks facility in Santa Clara, spoke at the recent Thin Film Summit in San Francisco. Most of his presentation on cost reduction potentials offered nothing out of the ordinary from the viewpoint of the industry’s cost reduction leader—such as the company’s targets of 52 cents per manufactured watt and at least 80MW run rate per production line by 2014.       

Yet at the end of his presentation, he talked about a few examples of “blocking and tackling” where First looks to “turn knobs” and make engineering improvements in the areas of run rate, conversion efficiency, and yields. He cited enhanced laser scribe throughputs, optimization of temperature ramp rates on glass (both heating up and cooling off), and improved module-lamination cycle times as focus areas. He also mentioned “lots of activity” looking at back contacts and what he called “new materials systems”—all done with cost reduction in mind.

Speaking of new materials systems, he wouldn’t confirm (or deny) First’s not-so-secret investigational efforts into CIGS. “We think about everything under the sun,” he said of the company’s disruptive technologies efforts. But he did opine that the key limitation to the quaternary TFPV compound is its manufacturability: “We haven’t seen proof yet that CIGS is manufacturable in high volume.”  

Several CIGS outfits have made great strides over the past year to counter Garabedian’s qualm. One example of improved manufacturing processes came out during a presentation by Air Liquide’s Ravi Laxman, whose company works closely on the materials supply, delivery, and abatement fronts with dozens of thin-film firms.    

Laxman talked about how the use of hydrogen selenide, a key ingredient in the CIGS film stack, has evolved for the better. After encountering process difficulties, several key customers of Air Liquide stopped using H2Se purified to four or five “nines” levels because of increased moisture concentration in the gas phase.

It seems as the cylinders emptied, the amount of H20 increased exponentially in the remaining gases, severely affecting the quality of the films and subsequently the performance of the modules themselves. As the impurities mount, the pipes handling the gases also show increased corrosion caused by higher H2Se and H20 content—a potentially bedeviling problem in the long term.

Tearing another page from the semiconductor playbook, the gas and chemicals vendor realized that the solution lay in improved handling of the H2Se feedstock and increasing the purity levels of the feedstock material, since higher purity gases cause less corrosion, according to Laxman.

Studies like those conducted by Air Liquide and its customers offer technologists a chance to get their geek on, and what better place for those propellers to spin than at two of the most important and prestigious PV conferences on the circuit: the 37th IEEE Photovoltaic Specialists Conference (IEEE PVSC)  and the 26th European Photovoltaic Solar Energy Conference (EU PVSEC).

Both events have issued calls for papers, and the submission deadlines are fast approaching. EU PVSEC, which returns to Hamburg on Sept. 5-9, has the earlier deadline--abstracts are due by Feb. 1. The IEEE PVSC, which takes place a few months earlier in Seattle on June 19-24, doesn’t need those abstracts until Feb. 22.

 Finally, a few random musings on a recent re-branding exercise from a growing force on the solar scene.

Since Korean chemical giant Hanwha bought 49.99% of Solarfun, the new partnership has been aggressively moving to join the top ranks of PV companies, staking out a more vertical position with moves up and down stream, including the most recent news of plans for another 2GW of cell and module production capacity.

The Solarfun board has also decided that it needed a name change to go along with the fresh game plan, and the company has (in)advertently completed a corporate rhyming couplet and officially become Hanwha SolarOne.

Considering the growing brand recognition of the Solarfun name, I wonder whether (a) the original moniker will continue to be used for the company’s modules, or (b) the Solarfun brand will be phased out entirely and eventually be replaced, by either Hanwha SolarOne or just plain SolarOne?

My inner brander tells me that the continuation of the Solarfun name or its replacement with the simple but catchy SolarOne would be preferable.  

Otherwise, people might ask, Hanwhat were they thinking?

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