One dimensional carrier trapping in the crystalline phase of a columnar liquid crystal

A study of charge transport in the crystalline phase of the columnar liquid crystal, hexakis(n-hexyloxy)triphenylene, HAT6, is reported. A simple model is introduced and fitted to observations of photocurrent transient decays in the crystalline phase of HAT6. From these a quasi one-dimensional trapping process is inferred with a field dependent trapping rate determined by carrier drift at high fields and controlled by carrier diffusion in the limit of zero field. The detrapping rate is found to be independent of field indicative of a neutral barrier. The trap concentration is found from fits of the transients to the model. The mobility of holes in the crystalline phase is found and compared to the time-of-flight mobility previously found for HAT6 in the discotic mesophase. Also found is the field dependence of the generation rate in the presence of an absorbing electrode adjacent to the photocreation site. (C) 1998 American Institute of Physics. [S0021-9606(98)70747-0].