Insertion of an organic interlayer for hole current enhancement in inverted organic light emitting devices

We report the enhancement of hole current density in the hole transport part of an inverted top-emission organic light emitted diode by applying an organic insertion layer of 1,4,5,8,9,11-hexaazatriphenylene-hexacarbonitrile (HAT-CN). Poor hole transporting performance of Al/4,4′-bis(N-phenyl-1-naphthylamino)biphenyl (NPB)/indium tin oxide is greatly improved by the HAT-CN insertion between Al and NPB layer. The highest occupied molecular orbital level onset of the NPB bends toward Fermi level at the HAT-CN/NPB interface. This extra charge generation layer made of pure organic molecules substantially enhances hole injection from Al anode as revealed by the results of ultraviolet photoelectron spectroscopy and J-V measurement data.