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

Abstract

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,C3 iridium acetyl-acetonate btp2Ir 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 btp2Ir 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.