Effects of ITO surface modification using self-assembly molecules on the characteristics of OLEDs

Indium tin oxide (ITO) has been commonly used as an anode of organic light emitting diode (OLED), because of relatively high work function, high transmittance, and low resistance. However, interface property between ITO and adjacent organic layer limits hole injection from the anode electrode. We have synthesized 4'-nitrobiphenyl-4-carboxylic acid (NBCA) and fabricated the hole-only device consisting of ITO/NBCA self-assembled monolayer (SAM)/TPD (1500 A)/Al (500 A) and the organic light emitting diode (OLED) consisting of ITO/NBCA SAM/TPD (600 A)/Alq(3) (600 A)/Al (600 A). The prepared hole-only device with NBCA exhibited lower driving voltage than the device using 4-nitrobenzoic acid (NBA). OLED using NBCA also showed high external quantum efficiency.