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.
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.
“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.