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Nanotube Bundles Show Promise for Solar Cells


Nanotube Bundles Show Promise for Solar Cells

J. Crochet/Los Alamos National Lab. A photon hits a bundle of carbon nanotubes and generates an exciton—an electron and hole bound together—and then they rapidly separate at an interface between tubes. Both steps are necessary to generate electric current in a solar cell. In isolated nanotubes, the exciton is reabsorbed before splitting apart.

Using thin-film photovoltaic materials as a cheap alternative to conventional solar cells has been a tempting but elusive goal because of their poor efficiency. In work published in Physical Review Letters, scientists at Los Alamos National Laboratory have shown that bundles of carbon nanotubes have the potential to dramatically increase the efficiency of thin films in capturing sunlight.

In the article, Chemistry and Materials Physics Applications division scientists describe a characteristic trait of a photovoltaic materials to strongly absorb light while simultaneously turning energy into a voltage through charge separation.

The major problem in taking advantage of this effect is that most materials that strongly absorb light have difficulty creating a voltage because the charges are unable to separate, which leaves energy in the material that is then is converted into light or heat.

A material that shows promise for solving this problem is semiconducting carbon nanotubes, which are tubules of the semimetal material graphene that are often described as one-dimensional channels that can transport photoexcited energy.

The Los Alamos scientists showed that when semiconducting carbon nanotubes are aggregated into tightly packed bundles, they begin to mimic the parent material graphene, and charge separation can be very efficient. Carbon nanotubes are not yet ready for use in commercial cells, but this effect is promising for incorporating the into photovoltaic devices as active layers where both light absorption and charge separation can occur. For more on this discovery, see the original article and a review paper describing the implications of this innovation.

http://prl.aps.org/abstract/PRL/v107/i25/e257402

http://physics.aps.org/articles/v4/108

December 21, 2011

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