Solar Tech: Carbon Nanotubes One-Up Photovoltaic Cells


Hollow tubes of carbon atoms, carbon nanotubes, can concentrate solar energy 100 times more than a regular photovoltaic cell, so say the chemists at MIT. The nanotubes could capture and focus light energy via antennas that allow smaller and more powerful solar arrays.
Michael Strano, research team leader, says: "Instead of having your whole roof be a photovoltaic cell, you could have little spots that were tiny photovoltaic cells, with antennas that would drive photons into them." Beyond housing, the antennas might be applied to night-vision goggles or telescopes.

Nanotube FillamentElectricity is generated by solar panels that convert photons [packets of light energy] into an electric current. The nanotube antenna increases the number of captured photons and transforms the light into energy that can be funneled into a solar cell. These antennas are a 10 micrometer, 4 micrometers thick, fibrous rope. The research team made a fiber of two layers of nanotubes with different electrical properties, or bandgaps. Electrons are the subatomic particles surrounding the nucleus of an atom that carry a negative charge. Bandgaps relate to how those electrons behave.

A graduate student working on the project, Geraldine Paulus, provided a photograph and explanation. "This filament containing about 30 million carbon nanotubes absorbs energy from the Sun as photons and then re-emits photons of lower energy, creating the fluorescence seen here. The red regions indicate highest energy intensity, and green and blue are lower intensity."

In any material, electrons can exist at different energy levels. The inner layer of the antenna contains nanotubes with a small bandgap, and nanotubes in the outer layer have a higher bandgap. When light energy strikes the material, all of the excitons flow to the center of the fiber, where they are concentrated, Strano?s team is the first to construct nanotube fibers in which they can control the properties of different layers.
Cost, as always is a factor in stimulating research into new ways to create energy. "At some point in the near future, carbon nanotubes – will likely be sold for pennies per pound, as polymers are sold," says Strano.