Single-walled carbon nanotube composites as hole injection layer for organic light emitting diode applications

Abstract

In this work, blends of dispersed short (∼500 nm) single-walled carbon nanotubes (SWCNTs) with poly(3,4-ethylene dioxythiophene):polystyrene sulfonic acid (PEDOT:PSS) were investigated as hole injection layers in OLEDs consisting of N,N′-di(naphthalene-1-yl)-N,N′-diphenylbenzidine (NPB) as a hole transporting and tris-(8-hydroxyquinoline) aluminum (Alq3) as electron transporting and emitting layer. The devices were characterized by electroluminescence and current-voltage measurements. By comparing the performance of devices fabricated using different surfactants (polyethyleneimine (PEI) and Gum Arabic (GA)) in dispersing SWCNTs and those prepared without surfactants, it was found that the use of appropriate surfactants can improve the OLEDs performance. Improved efficiency was obtained for optimized SWCNTs concentration compared to the devices with pure PEDOT:PSS, although maximum luminance is lower. The PEDOT:PSS:SWCNT nanocomposite layers are characterized and the reasons for the improved OLED performance are discussed. © 2005 Materials Research Society.