Multi-layer organic light-emitting diodes processed from solution using phosphorescent dendrimers in a polymer host

Abstract

A uniform dispersion of highly soluble phosphorescent dendrimer emitters is achieved by blending with a polymer host poly(9-vinylcarbazole) (PVK) containing N,N'-diphenyl-N, N'-(bis(3-methylphenyl)-[1,1-biphenyl]-4,4'-diamine (TPD) and 2-(4-biphen-4'-yl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD). No visible aggregation or self-quenching was observed for guest-to-host weight ratios of up to 33:67. The dendrimers contain a fac-tris(2-phenylpyridyl)iridium(III) [Ir(ppy)(3)] core, first generation biphenyl-based dendrons, and 2-ethylhexyloxy surface groups. The guest-host blend is used for all solution processed organic light-emitting diodes. A maximum external and current efficiency of 10.2% and 38 cd/A (at 5 V and a brightness of 50 cd/m(2)), and a maximum brightness of 27,000 cd/m(2) (at 14.5 V), were obtained when a CsF/Al cathode was used. Blade coating was used to fabricate a multi-layer structure that also contained an electron-transport layer. The device that had a LiF/Al cathode had a maximal efficiency of 40 cd/A corresponding to an external quantum efficiency of 10.8% (at 5 V and a brightness of 19 cd/m(2)). The maximum brightness of the second device was 17,840 cd/m(2) at 14 V. (C) 2010 Elsevier B.V. All rights reserved.