Organic photoreceptor compounds

Selenium was once a greatly used element in electronics. Its photoconductivity opened up applications as photocells and exposure meters. In the period 1970-1980 high-purity selenium compounds were dominant as photoreceptors on the drums of paper copiers. Organic photoreceptor compounds (OPC) have replaced them nowadays to a great extent. Selenium s role as a rectifier material has largely been taken over by silicon. 

The semiconductor selenium is an excellent photoconductor however, its photoresponsiveness decreases sharply at wavelengths over 550 nm, which has motivated research on organic photoconductive materials.1550,1551 Many different organic compounds display photoconductive behaviour, such as phthalocyanines (596 M = metal) or squaraines (597) (Figure 6.33) today more than 90% of xerographic photoreceptors are composed of organic photoconductors. 

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