New thermally cross-linkable polymer and its application as a hole-transporting layer for solution processed multilayer organic light emitting diodes

Abstract

A new thermally cross-linkable copolymer containing reactive benzocyclobutene (BCB) units and the well-known hole-transporting moiety N,M '-bis(3-methylphenyl)-N,N '-diphenylbenzidine) (TPD) was synthesized and characterized. Thermal annealing of spun-cast films of the copolymer, followed by cross-linking at 200 degrees C, led to insoluble polymer films with a smooth surface. Green emitting fluorescent OLEDs were fabricated using the new cross-linkable polymer and compared with conventionally prepared devices. Using the thermally cross-linked copolymer as a hole-transporting layer, solution processed multilayer light emitting diodes were prepared that exhibited high performance with 10.4% external quantum efficiency at a brightness of 350 cd/m(2).