Photoemission study of hole-injection enhancement in organic electroluminescent devices with Au/CFx anode

We demonstrate hole-injection enhancement from Au into N,N′-bis-(1-naphyl)-N,N′diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) by inserting between them a plasma-polymerized fluorocarbon (CFx) buffer layer. Ultraviolet and x-ray photoemission spectroscopic study indicates that chemically tailoring the Au surface with CFx can reduce the hole-injection barrier to ∼1 eV with respect to bare Au. This effect is ascribed to the buildup of an interfacial electric field, arising from the molecular dipolar characteristic of CFx. The present results suggest that CFx can function as a hole-injection enhancement layer for organic optoelectronic/electronic devices which use a metallic anode.