Optical ‘rectenna’ converts light into direct current
To create the "optical rectenna," the researchers used nanoscale components to fabricate tiny rectifiers onto metallic multiwall carbon nanotubes. The carbon nanotubes act as antennas to capture the oscillating waves of light – solar or otherwise – while the rectifiers, switching on and off at petahertz (1015-Hz) speeds, convert the light to dc as it passes through them (see video (1:30) below).
While the dc output from one rectenna is small and the efficiency demonstrated so far is below 1%, billions of rectennas could be combined into an array that could generate significant current, say the researchers. The devices could, they say, offer a new technology for photodetectors that would operate without the need for cooling, energy harvesters that would convert waste heat to electricity, and ultimately a new way to efficiently capture solar energy.
"We could ultimately make solar cells that are twice as efficient at a cost that is ten times lower, and that is to me an opportunity to change the world in a very big way" says Baratunde Cola, an associate professor in the George W. Woodruff School of Mechanical Engineering at Georgia Tech. "As a robust, high-temperature detector, these rectennas could be a completely disruptive technology if we can get to one percent efficiency. If we can get to higher efficiencies, we could apply it to energy conversion technologies and solar energy capture."
This image shows the components of the optical rectenna developed at the Georgia Institute of Technology. (Credit: Thomas Bougher, Georgia Tech)
The researchers hope to further increase the output and efficiency of the devices by changing the materials, opening the nanotubes to allow multiple conduction channels, and reducing resistance in the structures. These changes, they say, could reduce the resistance by several orders of magnitude and potentially yield an efficiency of greater than 40%.
Another goal is to fabricate the devices on a foil or other material that would allow flexible solar cells or photodetectors. According to the researchers, a rectenna with commercial potential could be available within a year. For more, see the paper published in the journal Nature Nanotechnology: "A carbon nanotube optical rectenna."
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