Charge Carrier Transport in Organopolysilanes and Its Application to Xerographic Photoreceptor

Abstract

The ionization potential and the hole drift mobility of organopolysilanes with different kinds of substituents were investigated for the best use of their high mobility in layered organic photoreceptors. The ionization potentials of alkyl-substituted organopolysilanes showing themochromic behavior were found to vary from 5.7 to 5.9 eV with themally induced reversible confomational changes in the Si backbone, while aryl-substituted organopolysilane gave a smaller ionization potential of 5.62 eV due to σ-&pai; mixing between Si backbone σ and side-group &pai; electrons. The hole drift mobility of organopolysilanes was found to be dependent on the σ-conjugation length in the Si backbone and successfully analyzed in the framework of Gill's empirical expression, which led us to the conclusion that the charge carrier transport in organopolysilanes is controlled by charge hopping through the intrinsic states derived from “domainlike” σ-conjugated segments of the Si backbone. Instead of “transport-inactive” binder polymers such as polycarbonate resin (PC) so far, organopolysilanes with high mobility and film-forming capability were shown to be useful for a “transport-active” polymer to be doped molecularly with low-molecular-weight charge carrier transport compounds. As an interesting result, the organopolysilane doped with a charge transport compound having the same ionization potential to organopolysilane host, gave the highest hole drift mobility of 10^-3 cm²/Vsec for amorphous polymeric solids. The layered photoreceptors consisting of organopolysilanes and organic pigments showed the high photo-sensitivity endurable for the practical use. The combinations with some organic pigments, however, were found to exhibit the anomaly in hole carrier injection from organic pigments to organopolysilanes contrary to a common knowledge in the usual organic layered photoreceptors. The doping technique improved the anomaly as well as some other practical problems. These results suggested that organopolysilanes are the promising material for the practical use in electrophotographic photoreceptors.