Photo-Patternable Hole-Transport Polymers for Organic Light-Emitting Diodes

A series of soluble arylamine-based hole transporting polymers with various ionization potentials have been synthesized. The synthetic methodology allows for substitution of aryl groups on the amine with electron-withdrawing and electron-donating moieties which permits tuning of the redox potential of the polymer. The arylamine-based monomers have been copolymerized with cinnamate-based moieties to obtain photo-cross-linkable polymers. These materials can be cross-linked and patterned using a standard mask aligner designed for photolithographic applications. UV cross-linking conditions were optimized to obtain an insoluble hole-transport layer with stable electroluminescent properties. Using a photolithographic mask, these materials have been patterned into 10−50-μm-size features. These polymers have been used as hole-transport layers (HTLs) in multilayer light-emitting diodes ITO/HTL/AlQ 3 /Mg:Ag [ITO = indium tin oxide, AlQ 3 = tris(8-hydroxyquinolinato)aluminum]. The electroluminescent properties have been evaluated and compared between devices made from polymers with different ionization potentials. Electroluminescent devices have been fabricated using a multilayered structure of spin-coated hole-transport materials to enhance the overall electroluminescent properties. Fully spin-coated devices have also been fabricated by spinning a blend of polystyrene and AlQ 3 on top of a cross-linked hole-transport layer.