Organic photoconductors carrier generation

The quantum efficiency for carrier generation in organics is strongly field-dependent and increases with the applied field. A theory developed by Onsager (30) for the dissociation of ion pairs in weak electrolytes under an applied field has been found to describe reasonably well the temperature and field dependence of the photogeneration efficiency in most of the organic photoconductors (3J). 

Most polysilanes show high photoconductivity, which has stimulated research of applications as organic photoconductors (OPC) in zerography. Carrier generation is, however, poor. Time-of-flight (TOF) studies revealed that holes are almost the sole carrier for most polysilanes (89) and the mobility (>= 10 cm W s) is 2-3 order higher than most carbon polymers (RilO cm AT s) (Table 4). 

Amorphous selenium metal was originally used as the photoconductor (photo charge carrier generator) of the Carlson process in electrophotographic reprography. Because of its toxicity and difficulty of fabrication, selenium was then replaced by organic photoconductor materials (OPC). 

Electrophotography is the only area in which the conductivity of sophisticated organic materials and polymers is exploited in a large scale industrial process today. Photoconductors are characterized by an increase of electrical conductivity upon irradiation. According to this definition photoconductive materials are insulators in the dark and become semiconductors if illuminated. In contrast to electrically conductive compounds photoconductors do not contain free carriers of charge. In photoconductors these carriers are generated by the action of light. 

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