Nanotubes May Revolutionize Solar Cells

February 07, 2002 by Jeff Shepard

The power output from solar cells may increase from a breakthrough in the use of carbon nanotubes. Researchers from Britain's Cambridge University (Cambridge, England) engineering department have developed photovoltaic devices that, when doped with single-wall carbon nanotubes (SWNT), perform better than undoped devices.

Nanotube diodes were made by depositing organic films containing SWNT on glass substrates coated with indium-tin oxide. Aluminium electrodes were then thermally evaporated under a vacuum to form a composite sandwich. The interaction of the carbon nanotubes with the polymer poly-3-octylthiophene (P3OT) allows excitons generated by light in the polymer to dissociate into their separate charges and travel more easily. The "super microscopic" material is 100 times stronger than steel and only one-fifth the weight, and is a superconductor.

The result is an increase in the electron mobility that balances the charge carrier transport to the electrodes. The doping of P3OT polymer diodes with SWNT improves the device's photovoltaic performance, increasing the photocurrent by more than two orders of magnitude and doubling the open-circuit voltage.

"The operating principle of this device is that the interaction of the carbon nanotubes with the polymer allows charge separation of the photogenerated excitons in the polymer and efficient electron transport to the electrode through the nanotubes," explains Emmanouil Kymakis, co-author of papers on the work. "The electrons travel through the nanotube length and then hop or tunnel to the next nanotube. The next stage of our research is the optimization of the device so it can be compared with other photovoltaic cells, which use different electron acceptors."