Jessika Trancik of the Santa Fe Institute, Scott Calabrese Barton of Michigan State University, and James Hone of Columbia University have recently combined forces toward improving solar cells. Their new research shows that a film of carbon nanotubes may be able to replace two of the layers normally used in a solar cell, with improved performance at a lower cost. The researchers have found a surprising way to give the nanotubes the properties they need by adding… defects.
Dr. Jessika Trancik
(Credit: Santa Fe Institute)
Current solar cells known as dye-sensitized solar cells have a transparent film made of an oxide that is applied to glass and conducts electricity. In addition, a separate film made of platinum acts as a catalyst to speed the chemical reactions involved. Both of these materials have disadvantages. On the one hand oxide films can't easily be applied to flexible materials as they perform much better on a rigid and heat resistant substrate like glass; on the other hand, expensive equipment is necessary to create the platinum films.
To solve both problems, the researchers decided to use carbon nanotubes to create a single layer that could perform the functions of both the oxide and the platinum layers. To do this, they needed the single layer to have three properties: transparency, conductivity, and catalytic activity. While ordinary carbon nanotubes films are so-so in each of these properties, when improving one, one of the other properties would have to be sacrificed. For example, making the film thicker makes it a better catalyst, but then it's less transparent.
Previous theory suggested that materials may function better as catalysts when they include tiny defects, providing sites for chemicals to attach; the researchers tried exposing the carbon nanotubes to ozone to roughen them up a bit, and they discovered that very thin films became dramatically better catalysts. In order to address the trade-off between transparency and conductivity, the researchers tried another trick on a bottom layer of tubes: they created carbon nanotubes that were longer to improve both conductivity and transparency.
In addition to improving solar cells, the new carbon nanotube films might also be used in the future to create improved fuel cells as well as improved batteries.
