Organic light-emitting diodes with multiple photocrosslinkable hole-transport layers

We report on photocrosslinkable hole-transport polymers and their use as photodefinable hole-transport layers in organic light-emitting diodes. The polymers were obtained by copolymerization of bis(diarylamino)biphenyl-based acrylate monomers with cinnamate-functionalized acrylate moieties. Polymers with a range of redox potentials were obtained by varying the substitution patterns of the bis(diarylamino)biphenyl units. The 2 + 2 cycloaddition of the cinnamate moieties following UV irradiation renders the material insoluble. This allows for patterning of the polymer and simultaneously enables the fabrication of multilayer structures from solution. Hole mobilities were measured in these copolymers with the time-of-flight technique. Their performance as hole-transport layers in light-emitting diodes, with tris(8-hydroxyquinolinato)aluminum as the emitter and electron-transport layer, is evaluated. Electroluminescent devices with multiple hole-transport layers having different ionization potentials were fabricated from solution, and the quantum efficiency of these devices was greater than that for devices based on a single hole-transport layer. (C) 2003 Wiley Periodicals, Inc.