Solar ♦ news digest
Technology Incubator contract to develop a commercial multi-junction cell using dilute nitrides, and also received more than $30 million of venture- capital funding for this commercialisation effort. To see more about NREL’s Incubator projects, see the NREL news release.
“So Solar Junction had this good idea. But now they had to prove that you could actually make a high- efficiency solar cell with this,” Friedman continues. “Otherwise, who cares? People can make a lot of claims, but it’s very simple to know whether you have a good solar cell or not - you just measure it.”
It didn’t take that long, Friedman points out. By 2011, NREL had certified a new efficiency record for Solar Junction’s SJ3 cell. The cell achieved an efficiency of 43.5 percent under concentrated sunlight, a significant step beyond the previous multi-junction efficiency record of 41.6 percent, and far beyond the maximum theoretical efficiency of 34 percent for traditional one-sun single-junction cells.
Dilute-Nitride Junction Eliminates Need for Heavy Germanium Layer
With the new dilute-nitride junction, the germanium layer, which constitutes about 90 percent of the weight of the cell, is no longer needed. That may not be a big deal when it’s part of a huge fixed utility-scale array.
But when solar cells are used to power satellites, reduction in weight means a smaller rocket is needed to launch into space, potentially reducing costs significantly. The lighter weight is also essential for the military, which is increasingly asking soldiers to carry backpacks that include solar devices to power electronics.
Serendipitously, if the germanium substrate is retained, it has essentially the ideal band gap of 0.7 eV for a fourth junction, perfect for capturing longer wavelengths of the solar spectrum. That paves the way for a 50 percent-efficient solar cell in the not so distant future.
The cost to manufacture the SJ3 cell is competitive with that of the industry-standard GaInP/GaAs/Ge cell, according to Solar Junction. Its greater efficiency translates to significant cost-of-energy savings.
An operator inspects a photolithography tool used to manufacture high-efficiency Solar Junction concentrator solar cells. NREL’s pioneering multi- junction work led to the Solar Junction SJ3 solar cell with tuneable bandgaps, lattice-matched architecture, and ultra-concentrated tunnel junctions. (Credit: Daniel Derkacs/Solar Junction)
“This is really a classic example of NREL developing something and then industry picking it up and running with it and making it a great commercial success,” Friedman mentions. “We started with some very basic materials research. We took it to the point where it made sense for industry to take over and take it to the marketplace.”
“We conceived the cell, demonstrated the individual parts, and let the world know about it,” Friedman comtinues. “But Solar Junction put all the parts together with record-breaking results, made it work with MBE, and commercialised it at a time when no one else seemed to be interested in or able to do it.”
And now, utilities are ordering the SJ3 cells so fast that Solar Junction has depleted its pilot-scale stock and gone into partnership with manufacturer IQE to
January/February 2013
www.compoundsemiconductor.net 173
According to a report released this fall from IMS Research, the CPV market is forecast to double in 2012 and reach almost 90 megawatts. The World Market for Concentrated PV (CPV) - 2012 predicts installations of CPV will grow rapidly over the next five years to reach 1.2 gigawatts by 2016.
Because of its design and size, SJ3 is an instant plug-in replacement for the standard cell now used by the space and CPV industries. So, for example, if a 40 percent-efficient cell were replaced with a 44 percent-efficient cell, this would instantly increase the entire system power output by close to 10 percent.
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