Metal/organic junction characteristics of vacuum-evaporated films of charge transfer complexes

Several donor-acceptor charge transfer (CT) complexes, having different degrees of charge transfer (ϱ) and different CT absorption bands(νCT), were successfully evaporated onto SiO2/n-Si substrates, yielding the device structures of metal/CT complex /SiO2/Si. The metal/organic junction characteristics were then investigated by measuring the displacement currents(Id), which are ascribale to the changes in charge densities for the devices, with respect to applying ac biases at low frequency. Different carrier injection behaviors were observed for the complexes examined. Perylene(Per)-TCNQ exhibited a predominantly electron-injective property, while for Dimethylphenazine (M2P)-TCNQ and Phenothiazine (PTZ)-TCNQ; whose absorption energies were much smaller than ca. 0.6 eV, both electron- and hole-injective characteristics were found. The results can be explored by taking into account the participation of charge carriers injected from metal electrodes. Also the carriers stem from thermal excitation within the CT complexes.