Efficient and color-stable white organic light-emitting diodes based on exciton management and phosphorescent sensitization

We report efficient and color-stable white organic light-emitting diodes (WOLEDs) by an approach combining the concepts of exciton management and phosphorescent sensitization to achieve 100% internal quantum efficiency and reduce efficiency roll-off. The approach employs a layer of 4-bis-(1-naphthyl-N-phenylamino)-biphenyl (NPB) as a fluorescent blue emitter to collect all singlet excitons for blue emission, and fac-tris(2-phenylpyridine) iridium(III) (Ir(ppy)(3)) as a phosphorescent emitter and sensitizer in other layer to harvest all triplet excitons for generating green light and sensitizing a fluorescent dye 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4Hpyran (DCJTB) for orange-red emission. By carefully adjusting the concentration of DCJTB and the thickness of the NPB layer, efficiency roll-off has been reduced and efficient balanced white light has been produced from the device ITO/PEDOT:PSS (30 nm)/poly(vinylcarbazole) (PVK):Ir(ppy)(3):DCJTB (100:5:0.4 in wt.) (60 nm)/NPB (4 nm)/2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) (10 nm)/tris(8-hydroxyquinoline)aluminum (Alq(3)) (20 nm)/LiF (1 nm)/Al. The operating principles have been studied and the results show that the long diffusion length of triplet excitons and long-range nonradiative energy transfer between the triplets of the phosphorescent emitter and the singlets of the fluorescent dye are crucial to realize white light emission. (c) 2013 Elsevier B.V. All rights reserved.