Photoreceptor Preparation

Organic photoreceptors can be prepared in either a flexible web or drum format. Webs are usually prepared on polymer substrates, polyethylene tere-phthalate being the most common. The substrates are between 100 to 200 pm in thickness and coated with a conducting surface layer. The substrates often contain layers on the reverse side for reduced curl, static discharge prevention, and control of frictional characteristics. The web configuration is also widely used for laboratory studies. For drums, the substrate is a metal cylinder, usually Al. Recently, however, drums of a poly(phenylene sulfide) resin doped with conductive C black have been developed (Kawata and Hikima, 1996). Drums are widely used in low- and mid-volume applications. Drums, however, are not well suited for research purposes. Thus, the preparation and characterization of drum photoreceptors is usually related to a specific application. 

For webs, the substrate electrode is usually a vapor-deposited, semitransparent metal layer (Ritchie and Fenn, 1987 Chen, 1993). Al, Ni, and Cr are commonly used. The use of semi-transparent electrodes permits the use of rear exposures for erase purposes. In the case of drums, the metal cylinder serves as the electrode. Usually, a thin, less than 1 pm, blocking layer is interposed between the electrode and the photoreceptor to prevent charge injection. This layer must not be so thick that a residual potential builds up during cycling. Many insulating polymers have been used acrylic polymers, epoxy resins, polyamides, polyesters, polyphosphazenes, polysiloxanes, polyurethanes, vinyl polymers, etc. 

For some applications, photoreceptors are prepared with surface layers for protection from chemical, radiation, and physical damage. Most surface layers are less than 5 pm. A key electrical requirement is the conductivity. If the layer is too insulating, a residual potential will build up during cycling. Thus, this 

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Figure 5 The field dependencies of the photogeneration efficiencies of single- and dual-layer photoreceptors prepared with AZO-FO. For the dual-layer structures, the transport layer contained a stilbene derivative (MAPS).

Umeda and Yokoyama (1997) measured photogeneration efficiencies of single- and dual-layer photoreceptors prepared with 4,4 -[(9,10-dihydro-9,10-dioxo-2,6-anthracenediyl)bis(azo)]bis[N-(3-bromophenyl)-3-hydroxy-2-naphth-alenecaiboxamide] (ABHN) (Hashimoto, 1985) and 4,4 -[l,4-phenylene-bis (2,l-ethenediyl-4,l-phenyleneazo)]bis[N-(2,4-dimethylphenyl)-3-hydroxy-2-na-phthalenecarboxamide] (PDHN) (Sasaki et al., 1980). For the dual-layer configuration, the transport layer contained MAPS. Single-layer photoreceptors... 

Hirao et al. (1995) measured photogeneration efficiencies of dual-layer photoreceptors prepared with generation layers of C q and C7q. The transport layers contained 22.5% N,N/-diphenyl-N,N,-bis(3-methvlphenyl)-(l,T-bi-phenyl)-4,4 -diamine. TPD. Figure 41 shows the spectral dependencies of the efficiencies computed on an incident photon basis. The efficiencies of C7q were somewhat higher than for C q. 

Figure 41 The spectral dependencies of the photogeneration efficiencies for dual-layer photoreceptors prepared with generation layers of C q and C q. The transport layer contained the triarylamine derivative TPD doped into PS.

The effects of the generation-layer fabrication variables on the sensitometry of a dual-layer photoreceptor prepared with bis(4-dimethylaminophenyl) squaraine (X = H in Appendix 2) have been extensively investigated by Law (1987). The charge acceptance, dark discharge, sensitivity, and the residual... 

The effects of peiylene structural modifications on the sensitometiy of duallayer photoreceptors prepared with vapor-deposited generation layers have been described by Loutfy et al. (1989) and Duff et al. (1990 and 1991). Attempts at extending the absorption into the near infrared have been described by Duff et al. (1993), Richter and Ackermann (1994), and Hor et al. (1996). 

Alkyl-substituted nitrated fluorene-9-ones were synthesized with the expectation of improved solubility and lowered toxicity (Loutfy and Ong, 1984 Loutfy et al., 1984 Ong et al., 1985). These showed improved solubility and somewhat improved mobilities compared to TNF. Studies of dual-layer photoreceptors prepared with (4-H-butoxycaibonyl-9-fluorenylidene)malonitrile transport layers have been described by Loutfy et al. (1984) and Murti et al. (1987). Low-field trapping was observed. The mobilities of this molecule in a polyester (PE) have been described by Borsenberger et al. (1990) and Borsenberger and Bassler (1991a). A transport layer with this molecule pendant lias been prepared and used with a TiOPc generation layer (Sim et all., 1996). A very significant residual potential was observed. For reasons that are not well understood, this is a common observation for dual-layer photoreceptors prepared with acceptor doped transport layers. The residual potential usually increases with cycling such that the useful process lifetime is limited. 

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