The charge carrier transport properties of neat thin films of red-, green- and blue-phosphorescence Ir complexes have been investigated in terms of time-of-flight transient photocurrent measurement. Bis(2-(2'-benzo[4,5-a]thienyl)pyridinato-N,C ^3')iridium(acetylacetonate) (btp₂Ir(acac)) (red-phosphorescence emitter) and iridium(III) bis[(4,6-di-fluorophenyl)-pyridinato-N,C ^2']picolinate (FIrpic) (blue-phosphorescence emitter) thin films exhibit bipolar charge transport. In contrast, the electron and hole transit signals of fac-tris(2-phenylpyridine)iridium(III) (Ir(ppy)₃) (green-phosphorescence emitter) thin films are unobservable. The charge carrier transport properties of thin films of an Ir-complex-doped 4,4'-N,N'-dicarbazole-biphenyl (CBP) and the appropriateness of FIrpic as a triplet-exciton and hole blocking layer are shown.

Low-frequency dielectric properties were measured for study of the transport properties of impurity ions in nematic liquid crystal (NLC: 4-cyano-4'-pentyl biphenyl) cells with and without polyimide alignment layers. It was found that the dielectric behavior of the NLC cells without polyimide alignment layers is due to the electrode polarization. The diffusion constant and the concentration of the impurity ions are determined from the dielectric behavior. The NLC cells with polyimide alignment layers exhibit interface polarization between the polyimide alignment layers and the NLC slab. The ion concentration is estimated from the frequency at the dielectric loss peak of the interface polarization. The ion concentration is much higher in the NLC cells with polyimide alignment layers than in the cells without polyimide alignment layers, indicating that a considerable amount of impurity ions are dissolved from the polyimide layers. The temporal variations of the dielectric properties of the NLC cells with and without polyimide alignment layers after the cell preparation were also measured.

The dielectric properties of nematic liquid crystal (4-cyano-4′-n-pentylbiphenyl: 5CB) cells in the ultralow frequency regime was investigated. A dielectric relaxation, whose relaxation time is 160 s, is observed at 303 K, and the dielectric relaxation is found to be independent of applied electric field. It is shown that the dielectric relaxation is caused by the Helmholtz double layer formed by the adsorption of impurity ions in 5CB onto the electrode surfaces of the cells, and hence the thickness of the double layer is comparable to the radius of impurity ions in 5CB. The dielectric relaxation obeys the empirical Cole-Cole circular arc law, indicating that dielectric relaxation times are distributed. The distribution of dielectric relaxation times can be explained in terms of distributed thicknesses of the Helmholtz double layer.

Charge injection and generation in nematic liquid crystal (NLC) cells have been studied by measuring the steady state currents and capacitances of NLC cells. The steady state current is attributable to the charge injection from the electrode at the lower applied dc voltages, while the steady state current is due to the generation of mobile ions by the Poole-Frenkel effect in the NLC bulk at the higher applied dc voltages. The width of electrical double layers, the desorption energy of the ions, and the interionic spacing of the positive and negative ions created by the Poole-Frenkel effect are estimated from the steady state current data.