The Chinese photovoltaic product manufacturer says that it recorded the efficiency, verified by the Solar Energy Research Institute of Singapore, on a production cell, using standard commercial-grade p-type silicon wafers. It adds that an efficiency of 21 percent is expected to be reached in the next six to 12 months.
In a statement released, the company says that it will now focus on commercializing the technology. "Suntech will advise when this technology is available in future releases of Suntech solar panels," it explains.
Researchers from Australia additionally tell pv magazine that the efficiency has been achieved through a resurface design of the Pluto cell. "The rear surface processing has been modified. One of the key improvements for the Pluto cell technology is the incorporation of similar high-efficiency characteristics of the record-holding PERL cell technology in the conventional Pluto cell manufacturing process.
"These act to improve the rear surface design of a conventional Pluto cell, primarily by reducing the metal/silicon interface area, while keeping the remaining non-contacted area well-passivated. In addition, Suntech has introduced process changes that minimize the use of high temperatures which make it possible to apply the high efficiency processes to the most commonly used commercial wafers."
The manufacturer added in its statement that the efficiency breakthrough represents its collaboration with worldwide research institutes, including Australias University of New South Wales. "Suntech will maintain and extend this collaboration through Suntech R&D Australia Pty Ltd, established in 2011, where project activities target the manufacturing implementation of advanced cell technologies," continues the statement.
During a fact finding trip to China in October 2010, pv magazine visited Suntechs headquarters in Wuxi to learn more about the companys activities. At the time, it said the development of its Pluto technology was one of the most exciting advancements it had made.
Reportedly delivering a 10 to 15 percent performance advantage, due to low reflectivity and reduced shading through the use of thinner metal lines, Pluto solar cells are based on the PERL, or passivated emitter with rear locally diffused technology. As such, they use the same materials, wafers and module line equipment as a standard cell. The difference, therefore, lies in the plating of the metals. In mass production, the technology has already been independently verified to reach efficiencies of greater than 19 percent: ultimately they are expected to hit between 22 and 23 percent.
In terms of Pluto implementation, the company intends to go through three phases, the first of which was already in commission in 2010, with 450 megawatts (MW) of cell production having been reached in the middle of the year.
The problem at the time was module encapsulation, however. "The module encapsulation at the moment is only working at about six MW per month – just under 100 MW a year," explained Wenham during the fact finding visit.
He went on to say there are two encapsulation options available. The first uses conventional encapsulation, which could be implemented immediately and would allow the company to scale up production. However, because Pluto has a "much better" response to all wavelengths of light than conventional solar cells, Suntech took a more unconventional route, which looked at interconnection.
"The alternative approach, which we have implemented in production at the moment, is a Pluto technology that has all these fine metal lines very closely spaced to each other to make the cell interconnect. Its a good way of doing it, provided you do the interconnect in the right sort of way." Suntech was confident the production equipment problem would be fixed later in the year, with the full half gigawatt of Pluto production operational by 2011. Responding to questions now, the researchers state that the Pluto production capacity is still at 450 MW.
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