Paper TF-ThP25
Enhanced Light-Emission Characteristics and Analyses of Electronic Band Structure of 2-TNATA / MoO_x for an Efficient Hole-Injection in Organic Light-Emitting Diodes

Thursday, November 12, 2009, 6:00 pm, Room Hall 3

Recently, the studies on metal-organic interfaces are concentrated in the efficient charge carrier-injection between electrodes and an adjacent organic layer adjoining to electrodes. The efficient carrier-injection properties are very important for improving a luminace and luminous efficiency in the field of the information display such as the organic light-emitting diodes, organic solar cells, organic thin film transistor, and organic sensors, and organic smart window devices. Here, we reported on the new hole-only contact system of 2-TNATA / MoO_x. The organic light-emitting diode with a glass / ITO (85 nm) / MoO_x (5 nm) / 2-TNATA (30 nm) / NPB (18 nm) / Alq₃ (52 nm) / LiF (1 nm)/Al (100 nm) structure showed higher luminous efficiency as two times than the device of the same structure with MoO_x of 0 nm-thick. The improvement of the luminous efficiency by inserting a MoO_x layer between tin-doped indium oxide (ITO) and 2-TNATA is attributed to the lowing of the barrier height in a hole injection (Φ_B^h) as well as the raising the band banding by pinning of Fermi level in the interfaces between two layers. The mechanism for a hole-injecting efficiency from anode to a MoO_x / 2-TNATA layer was proved by analyzing an ultraviolet photoemission spectroscopy (UPS) spectra. Φ_B^h in the 2-TNATA / MoO_x interface with MoO_x of 20 nm-thick was decreased about 2.0 eV, when compared to Φ_B^h of the pure layer with only 2-TNATA.

Keywords: organic light-emitting diode, electronic structure, interface, MoOx, 2-TNATA