Nanotube forms efficient solar cell

Researchers at Cornell University have identified yet another potential application for carbon nanotubes – touted as successors to silicon in integrated circuits – this time as efficient solar-energy converters.

The researchers fabricated, tested and measured a simple solar cell based on a photodiode structure using an individual carbon nanotube. Reporting their work in in the journal Science, the researchers – led by Paul McEuen, the Goldwin Smith Professor of Physics, and Jiwoong Park, assistant professor of chemistry and chemical biology – claimed they had observed “highly efficient generation of electron-hole pairs”, one of the processes need to convert solar energy to electricity.

“We are not only looking at a new material, but we actually put it into an application -- a true solar cell device,” said Nathan Gabor, a graduate student in McEuen's lab, a member of the Cornell team.

Their work was inspired in part by previous research in which scientists created a diode using a single-walled nanotube. The Cornell team wanted to see what would happen if they built something similar, but this time shined light on it.

Shining lasers of different colors onto different areas of the nanotube, they found that higher levels of photon energy had a multiplying effect on how much electrical current was produced.

Further study revealed that the narrow, cylindrical structure of the carbon nanotube caused the electrons to be neatly squeezed through one by one. The electrons moving through the nanotube became excited and created new electrons that continued to flow. The nanotube, they discovered, may be a “nearly ideal” photovoltaic cell because it allowed electrons to create more electrons using photon-supplied energy that is normally lost through heat.

Though they have made a device, scaling it up to be inexpensive and reliable would be a serious challenge for engineers, Gabor said: “What we've observed is that the physics is there.”

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