By Erin Weeks
Copper nanowires are one step closer to becoming a low-cost substitute for the transparent conductor in solar cells, organic LEDs and flexible, electronic touch screens. A team at Duke has succeeded in making transparent conductors from copper nanowires that are only 1% less transparent than the conventional material, indium-tin oxide (ITO).
Copper is 1000 times more abundant and 100 times cheaper than indium, the main ingredient in ITO, but for years copper nanowires have lagged behind in terms of transmittance.
Assistant chemistry professor Benjamin Wiley’s lab has fixed that — simply by changing the aspect ratio, or the proportion of length to diameter, of the nanowires. The findings were reported recently in the journal Chemical Communications.
“We finally have something competitive with ITO in terms of performance, and we got there by increasing the nanowire aspect ratio,” Wiley said.
Using a special growth solution, Wiley’s lab can “sprout” the nanowires in under half an hour and at normal atmospheric pressure. Further tweaking the synthesis, the team was able to prompt the nanowires to grow long and uniform in diameter, instead of tapered and baseball bat-shaped, which have lower aspect ratios.
The paper also includes the images of copper nanowire growth as observed in real time, the first time such observations have been published.
Still, at least one kink remains before the nanowire technology will be attractive for commercial production. The copper nanowires are susceptible to corrosive oxidation, which Wiley’s team has tried to remedy by coating the nanowires with materials like nickel. Unfortunately, a nickel coating reduces the transparency of the nanowire films.
“So now we’re trying to figure out ways to protect the nanowires without decreasing the performance,” Wiley said. “We’re focused on getting the same performance, but having more stability.”
Citation: “A rapid synthesis of high aspect ratio copper nanowires for high-performance transparent conducting films.” Shengrong Ye, Aaron Rathmell, et al. Chemical Communications, March 11, 2014. DOI:10.1039/c3cc48561g.