Excitonic versus transport dominated charge injection at a dye photoconductor interface

Utilizing the `time-of-flightʹ-technique with double layer cells of dye sensitized liquid crystalline hexahexylthiotriphenylene (HHTT), we investigated the influence of different charge generation mechanisms. In the case of the dye-layer titanyl-phthalocyanine, charge transport in the generation layer and charge injection significantly modifies the photo current transients as compared to the nearly rectangular transients of the HHTT transport layers. In contrast to this behavior, the photo current transients of an azo pigment show no modification due to the dye layer. We conclude that the processes in the azo pigment layer must be of excitonic nature.