To make the best solar cells flexible, researchers have to find the best conductive materials. Such conductors are silver and indium tin oxide (ITO) nanowires, but they have several drawbacks. The copper nanowires made using a method invented by Duke University chemists, on the other hand, are cheaper than silver and better (read more conductive) than carbon nanotubes.
Benjamin Wiley, an assistant professor of chemistry at Duke, along with his colleagues, report the finding of this technology in this week’s online edition of Advanced Materials.
“If we are going to have these ubiquitous electronics and solar cells,” Wiley said, “we need to use materials that are abundant in the earth’s crust and don’t take much energy to extract.”
He points out that there are very few materials that are known to be both transparent and conductive, which is why ITO is still being used despite its drawbacks.
Copper is a thousand times more abundant than indium, thus cheaper, and can also be used to make transparent and highly-conductive nanowires.
The researchers grew their copper nanowires in a water-based solution. “By adding different chemicals to the solution, you can control the assembly of atoms into different nanostructures,” Wiley said. In this case, when the copper crystallizes, it first forms tiny “seeds,” and then a single nanowire sprouts from each seed. It’s a mechanism of crystal growth that had never been observed before.
The technology that Wiley, together with Aaron Rathmell and undergraduate student Stephen Bergin have developed could fabricate nanowires from solution in a roll-to-roll process, somehow resembling newspaper printing. This would be much more efficient than the production process of indium tin oxide currently used.
One issue that the researchers confront is the clumping of copper nanowires, which affects their transparence. Another problem would be their oxidization, which affects their conductivity. The scientists are working around these issues, and once solved, they will scale the process up for commercial use. Wiley believes it won’t be very long until we will see this technology used in solar cells factories, in LCD displays and flat-panel TVs. These devices, is produced by using this technique, would be a lot cheaper than those being commercialized today.