PORTLAND, Ore. Carbon nanotube ink with 10 times the electron mobility of typical organic semiconductors has been developed using a new chemical process that helps solve the thorny problem of manufacturing nanotube thin films.
DuPont and Cornell University researchers claim 100 cm2 per volt-second electron mobilities for its new process, compared to 10 cm2 for typical organic semiconductors.
Organic semiconducting thin films of carbon nanotubes could enable flexible electronic devices to be printed at low temperatures on flexible plastic substrates. Current manufacturing processes for carbon nanotubes create a mixture of both semiconducting and metallic nanotubes, degrading the quality of thin-film transistors.
|Thin films of semiconducting nanotubes could enable flexible electronics and solar cells to be printed using cheap, low-temperature processing.|
DuPont claims to have perfected a simple chemical treatment process called cycloaddition that uses fluorine molecules to negate the effects of metallic nanotubes. The result is pure semiconducting films.
"Careful control of the [fluorine] chemical reaction enables the complete conversion of metallic tubes without the degradation of semiconducting tubes," said DuPont research fellow Graciela Blanchet.
The presence of metallic nanotubes combined with semiconducting nanotubes degrades the electrical characteristics of typical organic thin films. This results from excessive "off" currents.
Organic semiconductor manufacturers have tried many different methods for sorting metallic from semiconducting nanotubes, including attempts to use DNA. However, most techniques for eliminating metallic nanotubes also damage the semiconducting materials. The new cycloaddition process is claimed by researchers to have achieve high-electron mobilities combined with on-off ratios as high as 100,000:1. This could lead to high-quality semiconducting nanotube ink that can be economically produced with a simple chemical treatment.
Next the researchers plan to demonstrate working electronic devices using the cycloaddition process to prepare the thin films, including printed transistors on flexible substrates and organic photovoltaic cells.
Funding for the nanotube ink research was provided by the U.S. Air Force.