Improved Carrier Transfer in Red Organic Light Emitting DiodesDoped with Rubrene

A red organic light emitting diode doped with rubrene is constructed with the configuration of ITO/NPB/Alq₃: rubrene: DCM/Alq₃/LiF/Al. In the device, N,N'-bis-(1-naphthl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine (NPB) is used as the hole-transporting layer, tris(8-quinolinolato) aluminum (Alq₃) as the electron-transporting layer and Alq₃ doped with 5,6,11,12-tetraphenylnaphthacene (rubrene) and 4-dicyanomethylene-2-methyl-6- p-dimethyla- minostyryl)-4H-pyran (DCM) as the emitting layer. When the doping concentration of rubrene is 6% and that of DCM is 4%, red purity of the device is improved effectively. The experimental phenomena are explained as the result of the improved carrier transfer from rubrene to DCM.