Abstract
We have investigated the hole-injection characteristics from indium tin–oxide (ITO) into 4,4′,4″-tris{N,-(3-methylphenyl)-N-phenylamino}triphenylamine (m-MTDATA) and have measured the hole-carrier drift mobility of this compound in single-layer ITO/m-MTDATA/Au structures. We have found that ITO is able to provide trap-free space-charge-limited currents over a wide range of film thicknesses and have established unambiguously that the ITO/m-MTDATA is an ideal Ohmic contact at high electric fields. Our observations clarify the role of m-MTDATA as a voltage-lowering hole-injecting buffer layer in organic light-emitting diodes.