Sharp Hits Record 44.4% Efficiency for Triple-Junction Solar Cell

NREL sets a two-junction-cell high mark. Solar efficiency records continue to fall.

Eric Wesoff June 24, 2013

Eric Wesoff

Editor-at-Large
Greentech Media

Eric Wesoff is Editor-at-Large at Greentech Media. Prior to joining GTM, Eric Wesoff founded Sage Marketing Partners in 2000 to provide sales and marketing-consulting services to venture-capital firms and their portfolio companies in the alternative energy and telecommunications sectors. Mr. Wesoff has become a well-known, respected authority and speaker in these fields.

His expertise covers solar power, fuel cells, biofuels and advanced batteries. His strengths are in market research and analysis, business development and due diligence for investors. He frequently consults for energy startups and Silicon Valley's premier venture capitalists.

Multi-junction, compound-semiconductor solar cells from the III-V family are capable of gaudy efficiency numbers.

Researchers at NREL just announced a 31.1 percent conversion efficiency for a two-junction photovoltaic cell of less than 1 sun. The previous record was 30.8 percent and held by Alta Devices. The tandem cell was gallium indium phosphide on gallium arsenide and was developed within the SunShot program, aiming to build a 48-percent-efficient concentrator cell.

Sharp just hit a Fraunhofer-Institute-confirmed, world-record 44.4 percent for its triple-junction solar cell (at 302 suns). Last year, Solar Junction hit an NREL-verified 44 percent cell efficiency (at 947 suns).

"Sharp worked to widen the effective concentrator cell surface and ensure uniformity of width at the interface of the connecting concentrator cell and electrodes" to achieve the record, according to the company.

The hope is that these more efficient compound semiconductors can improve the economics of concentrated photovoltaics (CPV).

CPV has a few tens of megawatts in the field. The largest CPV deployment in North America is the 30-megawatt Alamosa site in Colorado owned by The Carlyle Group with hardware from Amonix. Soitec has large CPV plants in the works in the U.S. and South Africa.

Amonix had to shut down its Las Vegas production facility in July of last year and has gone quiet. SolFocus has been looking for a buyer for some time now; GreenVolts is out of business. JDSU has quietly exited the CPV cell market after acquiring QuantaSol.

Yet studies show 70 percent theoretical efficiencies from a 5- or 6-junction cell. Experts have suggested that 50 percent cell efficiency could be achievable in three to five years, which could get CPV module efficiencies to over 40 percent.

So great technological progress at the CPV cell level is being made by Sharp and Solar Junction (and Semprius, Emcore, and Spectrolab), but vendors have to aggressively cut cost at the systems level to keep up with the plummeting cost of single-axis c-SI. (We covered CIGS thin-film efficiency records here. And here's the take of an advanced silicon efficiency specialist.)

With the exception of a year or so when silicon prices went up, the LCOE value proposition for terrestrial CPV has always been a stretch. If flat-panel PV module and installation costs and PPA prices continue to drop to the depths that GTM Research forecasts, CPV's terrestrial future remains a very uphill battle.