Concentrated Solutions of Highly Conductive Pyrene-Functionalized Carbon Nanotubes Suitable for Printing

As produced, raw carbon nanotubes are not soluble in many solvents necessary for printing applications. Standard methods for circumventing this problem involve sidewall functionalization and surfactants. Sidewall functionalization invariably destroys the π-network that gives carbon nanotubes their useful electronic properties, while surfactants deposit an insulating layer onto the carbon nanotube surface that must be washed off to regain the desired properties. Non-covalent functionalization offers the possibility to achieve solubility without destroying the π-network, but published methods have resulted in relatively low concentrations or substandard electronic performance. We have developed a scalable method to non-covalently functionalize long (> 3 μm) carbon nanotubes with simple pyrene derivatives. This method produces highly dispersed solutions with concentrations as high as 2.5 g/l that can be used to produce conductive coatings with sheet resistance as low as 350 Ω/sq with 85% transmittance at 550 nm without post-deposition washing or doping treatments. The functionalized carbon nanotubes can be formulated into solutions that can be printed by ink-jet deposition, Aerosol-Jet® deposition, screen printing, and spray coating for printed electronics fabrication, and the solutions are stable for months without signs of bundling.