Formation of Ohmic hole injection by inserting an ultrathin layer of molybdenum trioxide between indium tin oxide and organic hole-transporting layers

摘要

Current density-voltage (J-V) characteristics of hole-only devices using indium tin oxide (ITO) anode and N,N'-diphenyl-N,N'-bis1-naphthyl)-1,1'-biphenyl-4,4'-diamine (α-NPD) layers were measured with various thicknesses of a molybdenum trioxide (MoO_3) buffer layer inserted between ITO and α-NPD. The device with a 0.75-nm-thick MoO_3 layer forms Ohmic hole injection at the ITO/MoO_3/α-NPD interfaces and J-V characteristics of this device are controlled by a space-charge-limited current. Results of X-ray photoelectron and ultraviolet/visibleear-infrared absorption studies revealed that this Ohmic hole injection is attributable to an electron transfer from ITO and α-NPD to MoO_3.