Solar Sandwich A Mighty Tasty Efficiency Upgrade

Can a sandwich make solar power more efficient? It might, if it’s a subwavelength plasmonic cavity sandwich as developed by Princeton University researchers.

Electrical engineer Steve Chou and his team say their layering of plastic and metal can keep light from reflecting from organic solar cells – and maybe conventional silicon panels, too – and capture more of the light that does enter the cell.

The layers of the “sandwich.” (image via Princeton University)

There are a couple of remarkable possibilities with this advance. First, there’s the degree of improvement the researchers are reporting – 175 percent greater efficiency of their cells. Second, the system is said to be ready for commercial use, with just a “transition period in moving from lab to mass production” necessary.

So, what have we really got here. In a news release, Princeton explained how this “sandwich” is put together:

The top layer, known as the window layer, of the new solar cell uses an incredibly fine metal mesh: the metal is 30 nanometers thick, and each hole is 175 nanometers in diameter and 25 nanometers apart. (A nanometer is a billionth of a meter and about one hundred-thousandth the width of human hair). This mesh replaces the conventional window layer typically made of a material called indium-tin-oxide (ITO).

The mesh window layer is placed very close to the bottom layer of the sandwich, the same metal film used in conventional solar cells. In between the two metal sheets is a thin strip of semiconducting material used in solar panels. It can be any type — silicon, plastic or gallium arsenide — although Chou’s team used an 85-nanometer-thick plastic.

The key here, Princeton says, is that the solar cell’s features are smaller than the wavelength of light being collected, turning it into a Roach Motel for light – photons can check in, but they don’t check out.

solar sandwich princeton

Electron microscope image shows gold mesh, with each hole 175 nanometers in diameter, smaller than the wavelength of light. (image via the Chou lab)

“It is like a black hole for light,” Chou said. “It traps it.”

If this is all it’s cracked up to be, it could be a game changer for organic solar cells. These are solar cells that use semiconducting plastics instead of the traditional silicon-based cells to produce thin-film solar delivery systems. Organic cells don’t have the efficiency of silicon-based cells, but they’re a lot cheaper.

So if the Princeton sandwich – called PlaCSH by the team, for “plasmonic cavity with subwavelength hole array” – can boost the efficiency of these organic cells, suddenly they could become much more viable. And, although they haven’t tested it on silicon panels yet, Chou and Co. think it could be a help there, boosting efficiency and making it possible “to reduce the thickness of the silicon used” by a thousand-fold.

Pete Danko is a writer and editor based in Portland, Oregon. His work has appeared in Breaking Energy, National Geographic's Energy Blog, The New York Times, San Francisco Chronicle and elsewhere.


  • Reply December 14, 2012

    Damon Hill

    As usual, no reference to any meaningful figures. How much energy does a square foot of this technology generate, compared to other photovoltaic technologies, and what is the cost per watt? I seldom see useful information on actual performance.

    • Reply December 14, 2012

      Pete Danko

      The claim is 175 percent improvement over “conventional solar cells,” which by context I assume they mean organic solar cells that achieve might achieve efficiency of 8 percent. That would put this technology up around 20 percent. As for cost, any estimate would be meaningless at this point, I think, since that would be highly dependent on how the technology were commercialized. It all sounds great, but as with all these claimed breakthroughs, it won’t be until the science moves a lot closer to actual manufacturing that we can make a real judgment.

Leave a Reply