materials consulting

Free-Volume Trapping in Multiactive Photoconductors, Michel (Mike) F. Molaire & al

free-volume trapping in single layer aggregate photoreceptor

NIP14: International Conference on Digital Printing Technologies, Toronto, Ontario, Canada  ISBN / ISSN: 0-89208-212-7

October 1998

The concept of free-volume trapping was first reported for single layer aggregate (SLA) photoconductors. The drying of SLA films, at temperatures above the glass transition temperature Tg   of  the SLA’s amorphous phase, followed by rapid cooling, generates excess free volume. It was proposed that excess free volume in the photoconductor film can act as a physical barrier to hole transport, amplifying hole range limitations.
We have studied this phenomenon in multiactive photoconductors with separate charge generation and charge transport layers, CGL and CTL respectively. We have found that trapping occurs in the CGL, suggesting some association with the generation process. Exposing at strongly absorbed wavelengths with generation at the CGL/CTL interface eliminates the problem.
We have also identified a class of hole transport materials that act as hole traps, when used in low concentration (below 15%) in combination with better transport materials. For example, the use of bis (diethylaminophenyl) diphenylmethane (0 to 4%), in combination with tri-p-tolylamine, substantially affects free-volume trapping in an aggregate-based multiactive photoconductor. Free-volume trapping impacts not only the film sensitivity, but also its cycling stability.