Organic Photoconductors

Cadmium Sulfide Photoconductor. CdS photoconductive films are prepared by both evaporation of bulk CdS and settHng of fine CdS powder from aqueous or organic suspension foUowed by sintering (60,61). The evaporated CdS is deposited to a thickness from 100 to 600 nm on ceramic substates. The evaporated films are polycrystaUine and are heated to 250°C in oxygen at low pressure to increase photosensitivity. Copper or silver may be diffused into the films to lower the resistivity and reduce contact rectification and noise. The copper acceptor energy level is within 0.1 eV of the valence band edge. Sulfide vacancies produce donor levels and cadmium vacancies produce deep acceptor levels. 

Photoconductors. Only the most recently developed organic photoconductors (OPC) approach optimum behavior (see Photoconductive POLYAffiRS). 

The trend in the xerographic copying and printing industry is to expand the use of organic photoconductors which are typically inexpensive and have a useful life. However, the a-Si H photoreceptors, even though more expensive to manufacture, may ultimately have an advantage in greater durabihty. 

Metal complex dyes and pigments perform key functions in both the image generation step and the toner development step. It is the metal complex pigment that produces the positive hole in the organic photoconductor. 

Koch-Yee Law. Organic photoconductor materials for xerographic photoreceptors (Advanced Tutorial A2). IS and T s Non-Impact Printing Conference 12, San Antonio, Texas, October 27, 1996. 

Poly-N-vinylcarbazole is one of the very important organic photoconductors now in use in electrophotography. For practical use, a little amount of sensitizer is usually added. 

Figure 2.37 The electrophotographic process using organic photoconductors (a) photocopying and (b) laser printing.

Coloured materials find application in both toners and organic photoconductors fused in electrophotography. Photoconductors will be covered in detail in Chapter 4 (section 4.4) and only toner resins will be considered in this section. 

Titanyl phthalocyanines are used as the CGMs in commercial organic photoconductors, e.g. in the engines from Canon, Xerox, Konica and other OEMs. 

Other molecular classes that have been used as CGMs in commercial organic photoconductors include quinones, e.g. dibromanthanthrone (4.24) by Xerox and Konica,... 

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