Bundled Nanotubes and Solar Power...

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

Thin-film photovoltaic materials are superior to conventional solar-cell materials, such as silicon, in that they are cheaper to make, are lighter and more flexible. They work by absorbing photons from sunlight and converting these into electron–hole pairs, known as "excitons". Then, in order to generate electric current, an electron and hole must be separated quickly before the two particles come back together and are reabsorbed into the material. In existing solar cells, these excitons are usually reabsorbed too quickly, leading to low efficiencies.

Jared Crochet and colleagues believe that this process of separation within thin-film solar cells can be facilitated by adding bundles of semiconducting carbon nanotubes. The researchers have discovered that while individual nanotubes are of little use, the efficiency can be improved if the nanotubes are bundled together into groups possessing the same chirality.

Physics World: Nanotube bundles could boost solar cells