PORTLAND, Ore.—Combining carbon nanotubes with a conductive polymer could enable transparent conductors that not only replace increasingly short supplies of indium tin oxide (ITO), but which are biodegradable to boot. The new transparent conducting film could be used in liquid-crystal display televisions, cell-phones, laptops and other displays as well as for solar cells.
Mass production of flat-panel displays has depleted the worldwide supply of the ITO material used to make the transparent conductors that enable their integrated thin-film transistors. As a result research labs worldwide are searching for a viable substitute, including recent startup C3Nano Inc. (Hayward, Calif.).
Now researchers at the Eindhoven University of Technology (Netherlands) have developed a replacement for ITO that can be produced with simple solution-based processing at room temperature using widely available carbon nanotubes mixed with a specially formulated latex polymer. The resulting conductive thin film makes scant use of nanotubes, which account for less than one percent of the material's weight, making it completely transparent and yet highly conductive.
The room temperature solution of nanotubes and conductive latex is heated, allowing its polystyrene beads to fuse together to form a thin film with an embedded network of nanotubes in its polymer matrix. The water is them removed by freeze drying, leaving behind a conductive film that can substitute for ITO.
Cor Koning (left) and Paul van der Schoot inspect the black pot containing a dispersion of carbon nanotubes in water, and the white pot which contains the conducting latex. Photo credit: Bart van Overbeeke.
The conductivity of the film demonstrated in the current research is still 100-times less conductive that ITO, but even so can be used for antistatic layers for displays and for EMI shielding. Next the team plans to increase the conductivity of the film by first the nanotube ingredient for higher conductivity and by refining their process.
The research team was led by professor Paul van der Schoot and polymer chemist Cor Koning with contributions from post-doctoral researcher Andriy Kyrylyuk.