Sensitized carrier generation in evaporated thin films and particle dispersions of benzimidazole perylene

Abstract

We studied photoconductivity in particle dispersions and vacuum evaporated films of benzimidazole perylene (BZP) pigment in contact with a tetraphenyldiamine (TPD) hole transport layer. Xerographic photoreceptors based on evaporated BZP photogenerator layers showed about two times higher carried generation efficiency than photoreceptors containing generator layer in the form of a particle dispersion. Time resolved fluorescence measurements were performed on these two types of structures. Fluorescence time evolution was compared in samples with and without TPD in a polycarbonate overcoat layer. Significantly larger decrease in average fluorescence lifetime was observed in structures containing thin evaporated films compared to the structures with the pigment in the form of particle dispersion. This indicates that reduced carrier generation efficiency in particle dispersion sin a consequence od exciton bulk trapping which significantly reduces the number of excitons reaching BZP/TPD interface. As carrier generation in BZP/TPD system is a result of exciton dissociation at the interface to produce electron-hole pairs. Thus a smaller number of excitons reaching the interface leads to reduction of carrier generation efficiency.