Photoconductor Fatigue. 3. Effect of Polymer on the Photooxidation of the Charge-Transport Layer of Organic Layered Photoconductors

Abstract

The photochemistry of hydrazone-based hole-transport molecules such as p-(diethylamino)benzaldehyde diphenylhydrazone (DEH) in organic photoconductors gives rise to fatigue of their initial electrical properties. These include an increase in dark decay rates and dark voltage drops and residual surface voltages after light decay. The type of electrical fatigue and its extent are strongly mediated by the polymeric host chosen for the charge-transport layer. We find that polymers such as polycarbonate or polymethacrylate are passive toward DEH photochemistry; in these materials the photochemical rate is high, resulting in large increases in residual voltage. Conversely, DEH photochemistry in polyesters affects the dark electrical properties to the extent that the photoconductor becomes persistently conductive. Acidity in the charge-transport layer and terephthalate versus isophthalate linkages in the polyester are important parameters; the terephthalate linkages exhibit considerable reduction of DEH photochemistry. © 1991, American Chemical Society. All rights reserved.