Mechanisms of enhanced hole-injection in organic light-emitting devices with MoO_3 layers

摘要

We demonstrate that the inserted hole injection layer MoO_3 between anode and Hole-Transport Layers, N,N′ -diphenyl-N,N′ -bis(1-naphthyl)-1,1′ -biphenyl-4,4″-diamine (NPB) effectively reduces the difference of NPB Fermi level to HOMO about 1eV than pristine NPB on ITO. The electronic structures and the interface chemistry studied by ultraviolet photoemission spectra (UPS) and core-level x-ray photoemission spectra (XPS) data show that the enhanced hole injection is associated with strong p-doping effects and the increases of hole concentration in the hole-transport layer is induced by MoO_3. All of the films are compared using density current-voltage (J-V) and quantum-efficiency (η-J) measurement.