Photoconductive polymers: A comparison with amorphous inorganic materials

Abstract

The transport properties of photo-induced charge carriers are a sensitive probe for the atomic or molecular structure of the involved materials. Whereas crystalline materials show high charge carrier mobilities which are independent of the experimental observation time, amorphous materials often show time dependencies of the respective dynamic transport parameters both, for materials with atomic disorder (amorphous silicon) and for materials with molecular disorder (amorphous polymers). A comparison of the pertinent transport parameters is made and the salient features of two common theoretical models are described (CTRW and multiple trapping). Comparing atomic (inorganic) materials and molecular, polymeric materials, the charge carrier mobilities of the presently available polymeric materials are comparatively low, yet, new synthetic approaches, using quasi-conjugated polymers show that organic materials have a high potential for improved properties. Due to their chemical stability, their high qualities as insulators with extremely high breakdown strengths and their chemical variability, organic polymers dominate many technical areas of photocopying and photoprinting. Therefore extensive synthetic work is in progress to further improve mobilities and new theoretical models are being developed which account for the energetic and geometric disorder of polymeric materials. It is interesting to note that, inspite of the structural differences, the theoretical models for inorganic and organic materials have much in common.