High-efficiency white light emission using a phosphorescent sensitizer in organic light-emitting devices

We have fabricated white organic light-emitting devices by using the phosphorescent material fac tris (2-phenylpyridine) iridium [Ir(ppy(3))] as a sensitizer, as a result, the efficiency of these devices is improved dramatically. Ir(ppy)(3) and the fluorescent dye 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9- enyl) (DCJTB) are co-doped into 4,4'-N,N'-dicarbazole-biphenyl (CBP) host, whose thickness affects both color and efficiency of the devices. Tris (8-hydroxyquinoline) aluminum (Alq) and 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (bathocuproine or BCP) are used as electron-transporting and exciton-blocking layers, respectively, and N,N'-diphenyl- N, N'-bis(1-naphthyl)-(1,1'-biphenyl)-4,4'-diamine (NPB) as a blue light-emitting as well as hole-transporting layer. The maximum efficiencies of the devices with 15 and 20 nm co-doped BCP tuning layer are 7.5 and 8.6 cd/A, respectively, and the former presents fairly pure white emission with CIE coordinates of (0.33, 0.32) at 10 V, which is very stable at various biases ( 10 - 19 V).