Observation of hole hopping via dopant in MoOx-doped organic semiconductors: Mechanism analysis and application for high performance organic light-emitting devices

Conduction mechanism in molybdenum trioxide (MoOx)-doped hole- and electron-type organic semiconductors is investigated. The used hole-transporting materials are N,N′-diphenyl-N,N′-bis(1-naphthylphenyl)-1, 1′-biphen4, 4′-diamine, 4′,4″-tri(N-carbazolyl)triphenylamine, 4, 4′-N,N-dicarbazole-biphenyl, and pentacene and the used electron-transporting material is (8-quinolinolato) aluminum (Alq3). It can be seen that the hole conductivity is significantly enhanced upon MoOx doping, and more importantly, dominant hole current could be realized in a typical electron-transport material Alq3 by doping MoOx. Hence, high efficiency organic light-emitting devices can also be achieved even using MoOx-doped Alq3 film as hole transporting layer. The mechanism investigation indicates that the MoOx plays an important role in the hole transport. It is showed that the MoOx serves as the hole hopping sites, whereas the used organic materials serve as the transport medium and determine the magnitude of transport current. Furthermore, it is found that doping MoOx into the organic materials also reduces the energy and position disorders of the doped organic films, which are well demonstrated by the study on transport characteristics of the doped films at various temperatures.