Efficient single layer RGB phosphorescent organic light-emitting diodes

We report efficient single layer red, green, and blue (RGB) phosphorescent organic light-emitting diodes (OLEDs) using a direct hole injection into and transport on triplet dopant strategy. In particular, red dopant tris(1-phenylisoquinoline)iridium [Ir(piq)(3)], green dopant tris(2-phenylpyridine)iridium [Ir(ppy)(3)], and blue dopant bis(3,5-difluoro-2-(2-pyridyl)phenyl-(2-carboxypyridyl)iridium [FIrpic] were doped into an electron transporting 1,3,5-tris(N-phenylbenzimidazole-2-yl)benzene (TPBi) host, respectively, to fabricate RGB single layer devices with indium tin oxide (ITO) anode and LiF/Al cathode. It is found that the maximum current efficiencies of the devices are 3.7, 34.5, and 6.8 cd/A, respectively. Moreover, by inserting a pure dopant buffer layer between the ITO anode and the emission layer, the efficiencies are improved to 4.9, 43.3, and 9.8 cd/A, respectively. It is worth noting that the current efficiency of the green simplified device was as high as 34.6 cd/A, even when the luminance was increased to 1000 cd/m(2) at an extremely low applied voltage of only 4.3 V. A simple accelerated aging test on the green device also shows the lifetime decay of the simplified device is better than that of a traditional multilayered one. (C) 2009 Elsevier B.V. All rights reserved.