Storage Lifetime of Polymer-Carbon Nanotube Inks for Use as Charge Transport Layers in Organic Light Emitting Diodes

The long-term stability of multiwall carbon nanotubes (MWCNTs) mixed with the hole-transport polymer Poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) has been examined. These surfactant stabilized solutions, used as transport layers in organic light-emitting diodes (OLEDs), are shown to be stable for periods of up to 15 months and show no signs of degrading soon after this time. In comparison, nonstabilized aqueous MWCNT solutions have been shown to aggregate within 30 min of production, and, although these aggregates can be redispersed, the solution displays an increase in smaller aggregates over time which cannot subsequently be redispersed by manual agitation. The stable MWCNT/PEDOT:PSS solutions have been used in ink-jet printing and as composite MWCNT/PEDOT:PSS films suitable as charge transport layers in spin-coated OLEDs.