Damodar M. Pai

Comparison of the drift mobility measured under transient and steady-state conditions in a prototypical hopping system

Abstract It is demonstrated that Au, Ag and carbon form ohmic contacts for hole injection in polycarbonate films doped with the hole-transporting molecule tetraphenyldiamine (TPD) and that these contacts are also ohmic on amorphous TPD films. At fields which make the injected hole transit time less than the bulk dielectric relaxation time, the response of these films, in a sandwich cell configuration with ohmic contacts, to step-field excitation is demonstrated to be a trap-free space-charge-limited (TFSCLC) current. The TFSCLC depends on the bulk drift mobility and the specimen dimensions only. These films provide a unique opportunity to examine simultaneously, in a dispersive transport medium, time-of-flight transit times, space-charge injection transients and finally steady-state SCLC. The latter collectively provide a measure of the drift mobility at different times in the same applied field. Thus the time-dependent character of the drift mobility can be fully delineated.

Hole transport in solid solutions of substituted triarylmethanes in bisphenol-A-polycarbonate

The time-of-flight and xerographic discharge techniques have been used to study electronic transport in films of dialkylamine-substituted triarylmethanes in bisphenol-A-polycarbonate binder. The hole mobility has been measured as a function of applied electric field, concentration of the molecules, and temperature. The results indicate that charge transport occurs by hopping among localized states associated with the molecule. In chemical terms, the hole transport involves a series of one-electron oxidation-reduction steps involving the organic molecules. The influence of some substituent groups on the electronic transport in these aromatic diamines has also been studied.

Polymers with photoconductive properties

Photoconductivity of organic polymers is reviewed. The current views on the mechanism of charge carrier generation and transport in sensitized and unsensitized polymers are presented. The known photoconductive polymers are categorized according to their structure into three basic groups: polymers with high degree of conjugation in the main chain, polymers with condensed aromatic groups and polymers with substituted arylamino functional groups.