Low efficiency roll off at high current densities in Ir-complex based electrophosphorescence diode with exciton diffusing and fluorescence compensating layers

Abstract

We demonstrate a fac-tris(2-phenylpyridine) iridium-based electrophosphorescent organic green-light emitting diode with a considerably reduced current-efficiency roll off at high current density. Such a low roll off of efficiency was achieved by inserting nondoped 4,4′-N,N′-dicarbazole-biphenyl (CBP) layer and a tris-(8-hydroxy-quinoline) aluminum (Alq3) layer between the emitting and electron-transporting layers to diffuse excitons from the emitting layer. The Alq3 layer is found to contribute as a complementary green fluorescent emitter at high current density. Thus, only a small decrease from 20.7to16.7cd∕A was detected in current efficiency when the current density increases from 3.9to100mA∕cm2. A high current efficiency of 12.6cd∕A was achieved even at 350mA∕cm2, indicating that the efficiency roll off was drastically reduced when compared with the device without CBP and Alq3 layers.