Preparation of Insoluble Hole-Injection Layers by Cationic Ring-Opening Polymerisation of Oxetane-Derivatized TriPhenylamineDimer for Organic Electronics Devices

We have demostrated that oxetane-derivatized hole conductors as well as electroluminescent polymers can be crosslinked via cationic ring-opening polymerisation (CROP) without deterioration of their electrical and electro–optical properties. This allows the fabrication of electronic multilayer devices via solution process. Here, we demonstrate three kinds of CROP crosslinking methods. They are (1) oxidative crosslinking, (2) photo crosslinking, and (3) trityl crosslinking. The crosslinking process parameters as well as the fluorescence characteristics and the solvent resistance of the resulting films have been investigated. The result shows that the oxidative crosslinking (1) gives the possibility to obtain the doping effect which increases the conductivity of the insoluble layer, although it reduces the fluorescence characteristics. The photo crosslinking (2) is controlled by irradiation; therefore, it gives the possibility to pixelate or pattern the film (lithography). It shows less fluorescence quenching than in (1). The trityl crosslinking (3) is suitable for the devices which are not pixelated and do not need the doping effect. Irradiation is not applicable here. Finally, we applied the insoluble layers in hole-only devices and blue-emitting OLEDs. We found that introduction of the layers improves the efficiency of the OLEDs.