Bright electroluminescence from single-layer organic light-emitting diodes comprising an ambipolar carrier transport layer of phenyldipyrenylphosphine oxide

We investigated the carrier transport and recombination characteristics of single-layer organic light-emitting diodes (SLOLEDs) composed of a phenyldipyrenylphosphine oxide (POPy2) layer doped with orange fluorescent molecules of 2,5-bis-[{bis-(4-methoxy-phenyl)-amino}-styryl]-terephthalonitrile (BST). The SLOLEDs achieved a high external quantum efficiency of 1.6% and a high luminance of 24,000 cd/m2 at a low driving voltage of 8 V. These very good electroluminescence characteristics originate from factors that include our use of the following: (1) the ambipolar POPy2 layer, which can transport balanced amounts of electrons and holes, (2) a high BST-doping concentration that traps injected carriers on BST molecules, and (3) insertion of an undoped POPy2 layer next to a metallic cathode to prevent exciton quenching.