Grafting Hole-Transport Precursor Polymer Brushes on ITO Electrodes: Surface-Initiated Polymerization and Conjugated Polymer Network Formation of PVK

We have utilized surface-initiated polymerization (SIP) to functionalize the conducting transparent electrode, indium tin oxide (ITO) with polyvinylcarbazole (PVK) brushes. Atomic force microscopy (AFM) imaging revealed smooth domains of grafted PVK and the composition, confirmed by X-ray photoelectron spectroscopy (XPS) measurements. The PVK is an electrochemically cross-linkable precursor by virtue of the pendant carbazole group and thus capable of forming conjugated polymer network (CPN) films. The electrochemical behavior and oligocarbazole CPN formation were evaluated by cyclic voltammetry (CV) measurements. The covalent linkage of the PVK brush allowed for a direct electroluminescent device preparation on SIP modified ITO in which PVK acts as a hole-transporting layer. In this case, the polyfluorene copolymer can be easily spin-casted on top of the grafted PVK without dissolution problems. This resulted in an improved polymer light-emitting diode (PLED) device behavior where the EL polymer layer can be simply solution cast on the modified ITO irrespective of solubility.