The effects of tris(2-phenylpyridine) iridium on the hole injection and transport properties of 4,4′,4″-tri(N-carbazolyl)-triphenylamine thin films

Abstract

The effects of tris(2-phenylpyridine) iridium [Ir(ppy)3] on the hole injection and transport properties of 4,4′,4″-tri(N-carbazolyl)-triphenylamine (TCTA) thin films have been investigated by current–voltage characteristic and admittance spectroscopy measurement. Dramatically improved hole injection can be achieved by inserting either pure Ir(ppy)3 or Ir(ppy)3 doped TCTA film between the indium–tin-oxide anode and TCTA layer, because of the hole transport ability and relatively higher-lying highest occupied molecular orbital (HOMO) level of Ir(ppy)3. When doping Ir(ppy)3 into TCTA, it acts as a role of trapping center and greatly reduces the hole mobility. Also, the hole transport properties in TCTA:Ir(ppy)3 thin films are greatly affected by doping concentration and show a nontrivial fluctuant dependence on the doping concentration. The origin of such dependence is discussed. This study provides insight into determining the charge carrier mobility of phosphorescent material doped organic semiconductor film.