Hole injection enhancement by sparsely dispersed Au nanoparticles on indium tin oxide electrode in organic light emitting devices

Gold nanoparticles stabilized by a hyper-branched polystyrene and adhered sparsely on indium tin oxide electrode can enhance hole injection to hole transport layer of N,N′-diphenyl-N,N′-bis(1-naphthyl)(1,1′- biphenyl)-4,4′-diamine. Although surface coverage by nanoparticles is less than 1%, the current density increases almost 1.5 orders of magnitude in hole-only device compared with the identical device without nanoparticles. This nanoparticle is also applied in typical organic light emitting diode. The driving voltage can be significantly lowered accompany with almost six times higher current density and luminance at 6 V. The local electric field induced by negatively charged nanoparticles should bring about the hole injection enhancement.