Researchers at MIT have developed a prototype all-carbon solar photovoltaic cell that produces electricity using near-infrared light. Typical silicon-based solar PV cells are only effective within the spectrum of visible light, leaving about 40 percent of the solar energy hitting the Earth essentially untapped.
Creating the first all-carbon solar cell comes as a result of recent developments in the large-scale production of purified carbon nanotubes, the essential ingredient of the device, along with c60 (a.k.a. “buckyballs“). ”It has only been within the last few years or so that it has been possible to hand someone a vial of just one type of carbon nanotube,” explains MIT professor Michael Strano.
Because the new cells are transparent to visible light, one very promising aspect of the research is the potential for creating hybrid cells. By overlying the new carbon cell over a silicon cell, a tandem solar cell could capture most of the energy from sunlight.
We won’t be seeing these “super solar cells” in our neighborhood solar panels quite yet. As the research team at MIT acknowledge, the proof-of-concept cells they’ve thus far produced suffer from the anticipated problem of efficiency. With an energy-conversion efficiency of only about 0.1 percent, work obviously remains on getting the new cells ready for prime time.
Much of the efficiency issue boils down to materials. Scientists are already aware of the inefficiencies of heterogeneous carbon nanotube mixtures as compared homogeneous nanotubes. Combining single-walled with multi-walled nanotubes are often so inefficient they don’t work at all. Researchers at MIT are focusing on ways to develop more precise control over the shape and thickness of the nano-material layers produced.
“It’s pretty clear to us the kinds of things that need to happen to increase the efficiency,” says Rishabh Jain, a graduate student at MIT. With proof-of-concept established, the MIT team expects other groups to step in and help iron out the challenge of increasing efficiency. ”We are very much on the path to making very high efficiency near-infrared solar cells.”
But it is significant even to have a relatively low efficiency cell able to harness the currently unused spectrum of light in the near-infrared and made at low enough cost. When paired with a conventional silicon-based PV solar cell, the new cell currently “growing up” in the labs at MIT may signal the future of solar cell technology. Ever toward the light!
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