In Situ Analysis of Hole Injection Barrier of Molybdenum-Oxide-Coated Anode with Organic Materials Using Synchrotron Radiation Photoemission Spectroscopy

We report the enhancement of the electroluminescent property of organic light-emitting diodes (OLEDs) using as a hole injection layer between indium tin oxide (ITO) anodes and -bis[ -(1-naphthyl)- -phenyl-amino]biphenyl . The operation voltage for of OLEDs with a 10 Å thick layer decreased from 24.5 to 14.7 V, and the luminescence value at increased from 1280 to . was deposited in situ on -plasma-treated ITO anodes and anodes coated with an -plasma-treated layer , and their interface dipole energies were quantitatively determined using synchrotron radiation photoemission spectroscopy. Secondary electron emission spectra after the deposition of on anodes revealed that the work function of is 0.55 eV higher than that of . The corresponding interface dipole energies were −0.20 eV for and −0.50 eV for . The hole injection barrier at the interface was reduced from 1.15 to 0.85 eV by the deposition of , resulting in an enhancement of the electroluminescence property of OLEDs.