This article briefly reviews (63 references) some of the important recent advances in composite organic photoconductors and also points out the likely directions for future research. Developments in the charge-generating and charge-transporting layers are considered separately. Included in the discussion are the dye-aggregate-based photoconductors, several types of pigment based charge generating layers (polyazo, perylene, and phthalocyanine compound classes) and some of the newer hole transporting materials. Electron transporting materials are briefly considered.

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In the color system with a non-linear image output printer consisting of both additive/subtractive mixture, e.g. color copier and offset printer, it is very difficult to predict the influence of color separation on color reproduction. So, for designing the spectral response of color image scanner, colorimetric quality factor is used to evaluate the response; however, it is not quantitative.
Authors propose the quantitative colorimetric model of a color image scanner that analyzes the color change on the chromaticity diagram caused by color separation, illumination and dark level correction. Based on the model, the spectral response of color image scanner has been developed that gives the same output for metameric colors.

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The Study of the layered photoreceptor using the ZnO fine particles as a carrier generation material have been done. The ZnO fine particles with a large specific surface area were prepared by gas-phase oxidation of zinc metal vapor. The relationship between excess zinc, specific surface area of the ZnO fine particles and photoreceptor property were investigated. These particles were effective for the layered photoreceptor as a carrier generation material. The photosensitivity of E1/2 = 1.6 lux · sec was obtained by the use of ZnO particles with a specific area 20 m²/g.

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Hydrogenated amorphous silicon (a-Si:H) photoreceptors coated with amorphous silicon carbide (a-SiC:H) films become to be wettable with increasing the cycles of corona discharge and consequently the printing image becomes to be unclear when the printing is done under the high humidity. An XPS analysis shows that the relative intensity of O_1s/Si_2p for a-SiC:H films increases with the cycles of corona discharge. The a-SiC:H films become to be wettable by the formation of SiO.
Hydrogenated amorphous carbon (a-C:H) and fluorinated amorphous carbon (a-C:F:H) films are investigated for the surface passivation films on a-Si:H photoreceptors. These films are more hydrophobic and stable after corona discharge than a-SiC:H films. In the cyclic test of the corona discharge and light exposure, a-Si:H photoreceptors coated with a-C:F:H films have much longer life-time than those with a-SiC:H films in terms of printing sharp image.

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D. C. transient currents under low-voltage application were measured for various organic layered photoreceptors with different ionization potentials of charge generation (CGM) and charge transport materials (CTM) in order to elucidate their energy level matching for carrier injection. It was observed that the hole injection occurred efficiently between CGM and CTM having the same ionization potentials. These results corresponded well to the residual potentials rather than photosensitivities in the xerographic measurment of these photoreceptors. The D. C. transient current measurment was shown to be useful to obtain the information about carrier injection paths through the various energy states of charge generation layer (CGL).

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