Electron and hole transport in a wide bandgap organic phosphine oxide for blue electrophosphorescence

We report blue phosphorescent organic light-emitting devices (OLEDs) using an ambipolar host, N-(4-diphenylphosphoryl phenyl) carbazole (MPO12), doped with iridium (111) bis[(4,6-difluorophenyl)-pyridinato-N, C(2)']picolinate (FIrpic). The external quantum efficiency and operating voltage is 9.1(-0.1)% and 4.8 V, respectively, measured at a brightness of 800 cd/m(2) with no outcoupling enhancement. By varying the layer structure of the OLEDs, we show that MPO12 is capable of transporting both electrons and holes, in contrast to previous demonstrations using diphosphine oxides, which only transported electrons. The improved hole transport results in improved device efficiency. (c) 2008 American Institute of Physics.