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

Current density-voltage (J-V) characteristics of hole-only devices using indium tin oxide (ITO) anode and N,N(')-diphenyl-N,N(')-bis(1-naphthyl)-1,1(')-biphenyl-4,4(')-diamine (alpha-NPD) layers were measured with various thicknesses of a molybdenum trioxide (MoO(3)) buffer layer inserted between ITO and alpha-NPD. The device with a 0.75-nm-thick MoO(3) layer forms Ohmic hole injection at the ITO/MoO(3)/alpha-NPD interfaces and J-V characteristics of this device are controlled by a space-charge-limited current. Results of X-ray photoelectron and ultraviolet/visible/near-infrared absorption studies revealed that this Ohmic hole injection is attributable to an electron transfer from ITO and alpha-NPD to MoO(3). (c) 2007 American Institute of Physics.