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Thickness independent initial PIDC slope through a thin light absorbing overcoat

IP.com Disclosure Number: IPCOM000033693D
Publication Date: 2004-Dec-23
Document File: 4 page(s) / 205K

Publishing Venue

The IP.com Prior Art Database

Abstract

This invention proposes to add a thin, light-absorbing layer on the top of the photoreceptor. The wear of the top layer will result in a reduced absorption. As result more light will be transmitted to the generation layer to compensate for the loss in sensitivity due to the thinner device thickness.

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Thickness independent initial PIDC slope through a thin light absorbing overcoat.

The collection efficiency (the ratio of the number of discharging charge carriers to the number of incoming photons) of high sensitivity photoreceptors runs into saturation at elevated fields (typically at a few l05V/cm).  As a consequence the PIDC (photo induced discharge curve) will change its shape with changing device thickness.  This change may become a problem when the photoreceptor is worn thinner with increasing print number.  In print engines with no feedback to compensate for the PIDC change this shortcoming can be resolved by increasing the exposure power as a function of print number.

However, if there is a thickness variation within the photoreceptor drum is caused by differential wear or bad coating, the spatial changes in PIDC cannot be compensated by adjusting the exposure power with print number. 

This invention proposes to add a thin, light-absorbing layer on the top of the photoreceptor. The wear of the top layer will result in a reduced absorption. As result more light will be transmitted to the generation layer to compensate for the loss in sensitivity due to the thinner device thickness.

Figure 1 represents the device before and after wear.  The blue layer of thickness sa is the light absorbing overcoat.  This overcoat should absorb in the wavelength of the writing laser or exposing light.  It is not required that the layer absorbs all the light; only parts of it.  As will become clear, not much light needs to be absorbed.  This would require only a slightly stronger light source, which is with today’s technology not a serious problem.  Figure 2 shows the collection efficiencies for both cases of Figure 1.

Macroscopic Field E

 
 

An infinitesimal discharge dV of the photoreceptor charged up to the potential V1 is governed by

For the special case of no absorbing layer and emission limited exposure this leads to

 

                                                                                (5)

which is the well-known proportionality requirement for thickness independent PIDC. In general this requirement is hard to satisfy for high sensitive photoreceptors since close to saturation one always has

Requirement in Eq. 4 is valid only for fields around El; hence, it will minimize changes in dV/dX but not completely remove them since this would require a field dependent absorption.  However, for reasonably thick photoreceptors this is not too much of a problem.

For the emission limited PIDC Eq. 2 has to be integrated into a range below E where the linearization aro...