America is dependent on foreign oil, said Dr. Ted Sargent, yet enough energy to power the country thousands of times over falls on its surface each day. In about a decade, though, cheap and flexible nanotechnology-enabled solar cells, however, could help change that. Sargent’s presentation on Sunday kicked off the Royal Canadian Institute’s fall Sunday lecture series.
The main snag currently solar cells face is their abysmal efficiency-currently hovering between three and five per cent. Part of the reason, explained Sargent, is because half the energy reaching the Earth is in the infrared part of the spectrum, where current solar cell technologies can’t harvest it.
But in a Nature Materials paper earlier this year, Sargent’s research group described how they did just that. They sandwiched thin layers of semi-conductors, each layer with semi-conductor particles of a different size. Each layer absorbed light of a different frequency in the infra-red spectrum to produce current.
Best of all, “all of the synthesis occurs in solution, and all of the semi-conductor processing is done by painting things on other things,” Sargent said. Unfortunately, their device was only 0.001 per cent efficient.
But they have been working at it, and, in an upcoming paper in Applied Physics Letters, describe how they increased its efficiency 1,000-fold. Sargent reckoned a further 10- to 100-fold efficiency increase is needed to make such devices work well.
And combining his infrared-harvesting solar cells with traditional solar cells could help cross the ten per cent efficiency threshold, the point at which large, cheap, and flexible solar cells will become commercially viable.
“We need it to be so cheap and flexible you could wear it,” he said. “We need it to be like a carpet-you go into Canadian Tire, you pay $100, you walk out with your solar carpet [and then] roll it across your rooftop.” Flexible solar cells, Sargent estimated, are still about 10 years away. But potential applications already abound.
Konarka Technologies, a Massachusetts-based company, is putting such cells on tents. “They’re now building tents for the US Army, solar tents,” said Sargent. “Soldiers can go out in the desert, pitch a tent, and get all the energy they need.”
Another idea, floated by the US Navy, is to paint aircraft with solar material. “It has the potential to enable aircraft which don’t have to get refuelled,” Sargent said. Painting its underside with the stuff could allow aircraft to fly at night, since the Earth emits energy even when it’s dark-but in the infrared part of the spectrum.
