Ultra-high efficiency by multiple emission from stacked organic light-emitting devices

We investigated the charge generation characteristics of intermediate layer, consisting of an organic acceptor material 1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile (HAT-CN6) and an organic donor material N,N'-di(naphthalene-1-yl)-N,N'-diphenylbenzidine (NPD), for a stacked organic light-emitting device (OLED). A stack consisting of an ultrathin 1 nm of LiF and of Al was used as an electron-injection layer (EIL) from HAT-CN6 to an adjacent electron transporting layer (ETL). The orange-emitting fluorescent stacked OLED with the charge generation layer and the electron injection layer exhibited twice higher current efficiencies and a longer operational lifetime than those of the corresponding unstacked device under a high luminance. We also fabricated a green phosphorescent OLED showing an extremely high current efficiency of 256 cd/A. (C) 2011 Elsevier B.V. All rights reserved.