Charge transport and charge generation in the bulk and at interfaces: discotic hole conductors versus amorphous hole conductors

We describe two methods by which discotic liquid crystalline (LC) triphenylene materials can be sensitized for wavelengths of the visible spectrum and the near IR. One way of doping is more conventional and uses bi-layers between the LC-system and an adjacent pigment layer. The second doping is achieved by a molecular doping with C₇₀. Here the influence of doping on the measured mobilities is much smaller as compared to the influence of doping measured in amorphous systems. We attribute this smaller influence of the C₇₀-doping on the mobility to a partial phase separation occuring between the LC-host material and the C₇₀-guest molecules. In our comparative experiments on doped dimethyl-triphenyldiamines we can show taht the magnitude of the trap depths for hole-trapping has a very large influence on the measured transport parameters.