Efficient Xerographic Photoreceptors from Conjugated Polymers and Polymer Blends

Bilayer xerographic photoreceptors in which ^-conjugated polymers and binary conjugated polymer blends are used as the charge generation layer have been fabricated, evaluated, and shown to be highly efficient. Devices incorporating poly(l,4-phenylene benzobisthiazole), poly(2,5-pyridylene benzobisthiazole), poly(l,4-phenylenebisvinylene benzobisthiazole), poly(l,4-(2-hydroxy)phenylene benzobisthiazole), and poly(benzimidazobenzophenanthroline ladder) as the charge generation layer and a layer of tris(>-toIyl)amine (TTA) dispersed in polycarbonate as the charge-transport layer showed good photosensitivities (6-18 ergs/cm ), good dark decay characteristics (2-10 V/s at surface potentials of 400600 V), and high charge generation quantum efficiencies (20-50% at ~10 V/cm). Photoreceptors using binary blends of conjugated polymers had enhanced spectral range of photosensitivity (300-700 nm) and significantly enhanced quantum yield for charge photogeneration relative to the component conjugated polymers. Photocamer generation in these bilayer photoreceptors is extrinsic in nature and is mediated by exciplex formation between the conjugated polymer and TTA at the bilayer interface. Observed nanoscale size effects, in which the photoreceptor performance (quantum efficiency, photosensitivity) is enhanced with decreasing size of the charge generation layer, provide a means of tuning the photoconductive properties of optoelectronic devices based on conjugated polymers. A model derived from Onsager's 1934 theory was used to estimate the primary quantum yield of ion-pairs and ion-pair separation distance in the bilayer photoreceptors to be 0.21-0.62, and 4-6 Ä, respectively.