Carbon nanotube solar cells have long been viewed as being a photovoltaic technology that possesses considerable potential for wide-scale commercial use — thanks to their very light, flexible, and relatively cheap nature.
And now, thanks to new research from the McCormick School of Engineering, that potential is much closer to being exploited — researchers there having created a new type of carbon nanotube solar cell that is more than twice as efficient at converting sunlight into electricity as previous designs. That said the energy conversion efficiency is still tiny.
“The field had been hovering around 1% efficiency for about a decade; it had really plateaued,” stated Mark Hersam, a professor of materials science and engineering at the McCormick School of Engineering. “But we’ve been able to increase it to over 3%. It’s a significant jump.”
The new carbon nanotube solar cell is also the first of its type to have its performance certified by the National Renewable Energy Laboratory.
Northwestern University provides details on the work:
The secret lies in the CNTs’ chirality, which is a combination of the tubes’ diameter and twist. When a thin sheet of carbon is rolled into a nanotube, several hundred different chiralities are possible. In the past, researchers tended to choose one particular chirality with good semiconducting properties and build an entire solar cell out of that one.
“The problem is that each nanotube chirality only absorbs a narrow range of optical wavelengths,” Hersam explained. “If you make a solar cell out of a single chirality carbon nanotube, you basically throw away most of the solar light.”
Hersam’s team made a mixture of polychiral, or multiple chirality, semiconducting nanotubes. This maximized the amount of photocurrent produced by absorbing a broader range of solar-spectrum wavelengths. The cells significantly absorbed near-infrared wavelengths, a range that has been inaccessible to many leading thin-film technologies.
Now while those improvements certainly mean a lot for the specific technology of carbon another solar cells, in a wider context those numbers are still lacking, as far as commercial applications go.
“If you look at our performance, there’s certainly a big jump,” Hersam stated. “But there’s more work to be done. We still have to advance this technology by a factor of three to five.”
The new research was just published in the journal Nano Letters.
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