Study of the Photoconductivity Mechanism in Phthalocyanine Pigment Particles by Electric Field Modulated Time Resolved Fluorescence

摘要

Phthalocyanine pigment particles represent an important class of organic photoconductors, which are extensively used in organic xerographic photoreceptors. Despite numerous studies, a complete picture of the carrier generation process in this class of materials has yet to emerge. In this paper we will present a detailed description of the photocarrier generation mechanism in TiOPc(I), TiOPc(IV), HOGaPc and x-H_2Pc. We have studied the influence of electric field on both the integrated and time resolved fluorescence in photoconductive particles dispersed in a polymer matrix. Time resolved fluorescence decays were analyzed by fitting the data to a sum of two exponentials representing the fast and slow fluorescence components. For HOGaPc, TiOPc(Ⅰ) and TiOPc (Ⅳ) the fast fluorescence component exhibits both amplitude and lifetime quenching. These results indicate that carrier generation in HOGaPc, TiOPc(Ⅰ) and TiOPc (Ⅳ) originates from both relaxed and nonrelaxed intrinsic excited singlet states, while the trapped excitons do not lead to significant carrier production. In contrast, for x-H_2Pc significant amplitude quenching of the fast component is observed only at high field and the trapped excitons are an important source of photogenerated carrier. This indicates that x-H_2Pc possesses at least some bulk sensitized photocarrier generation. All of the phthalocyanines studied exhibited a quadratic dependence of integrated fluorescence quenching on electric field indicating the existence of a neutral carrier precursor state.