Electroluminescence characteristics of n-type matrix materials doped with iridium-based green and red phosphorescent emitters

The electroluminescence characteristics of various n-type matrix materials with various orders of electron mobility doped with the phosphorescent green emitter fac-tris(2-phenylpyridine) iridium(III) [Ir(ppy)(3)] and the phosphorescent red emitter bis(2-(2'-benzo [4,5-a] thienyl)pyridinato-N,C-3')iridium(acetyl-acetonate) [btp(2)Ir(acac)] were evaluated and compared to those of the p-type 4,4''-N,N'-dicarbazole-biphenyl (CBP) reference matrix. For Ir(ppy)(3), the device with the n-type matrix 1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene was found to have the highest efficiency and operational lifetime, whereas for btp(2)Ir(acac) the device with the p-type matrix CBP was found to have the highest efficiency. Our study of hole- and electron-dominant devices and analyses of electroluminescence spectra show that the main recombination zone position and the electron-hole balance change as the matrix material changes, resulting in changes in the characteristics of the organic light emitting diodes. (C) 2008 American Institute of Physics.