Ultraviolet Light Photofatigue of Organic Photoreceptors

Abstract

Organic photoreceptors (OPC) are organic-chemical-based photoelectric transducers. For optimum performance in an electrophotographic (EP) process, the OPC dark and photoelectrical characteristics must be stable. Exposure of the device to ultraviolet light (UV) may cause undesirable performance changes (fatigue) as a function of EP cycling. We have previously shown that for OPCs formulated with triarylamine-based charge transport materials (CTM), the CTMs undergo photochemical reactions that cause the observed UV fatigue. The addition of specific electron-deficient acceptors to the charge transport layer (CTL) formulation can substantially reduce or eliminate UV fatigue. Based on analysis of the photophysics of acceptor-doped CTL systems, we propose a mechanism for UV fatigue reduction that invokes energy transfer from the excited singlet state of the CTM to donor-acceptor charge-transfer sites in the CTM-polymer binder coating. Using the photophysics as a guide, several classes of chemicals, both monomeric and polymeric, have been identified and shown to be effective in reducing UV photofatigue in OPCs.