Properties of Interface between Organic Hole-Transporting Layer and Indium Tin Oxide Anode Modified by Fluorinated Self-Assembled Monolayer

Abstract

The electronic structure and chemical properties of the interface between indium tin oxide (ITO) modified by a fluorinated self-assembled monolayer (F-SAM) and a N,N '-bis(1-naphthyl)-N,N '-diphenyl-1,1'-diphenyl-1,4'-diamine (α-NPD) layer were investigated in order to clarify the effects of the F-SAM modification of ITO anodes on the driving voltage and lifetime of organic light-emitting diodes (OLEDs). Ultraviolet and X-ray photoelectron spectroscopy revealed that the F-SAM modification of ITO led to a shallower highest occupied molecular orbital level in the α-NPD layer near the interface than in conventionally treated ITO, a chemical reaction between F-SAM and α-NPD, and the migration of adsorbed fluorine into the α-NPD layer. These results indicate that high conductance, the suppression of crystallization, and the inhibition of oxidation in the hole-transporting layer along with a small hole-injection barrier height at the anode/HTL interface contribute to the excellent properties of OLEDs having ITO anodes modified by F-SAM.