Transient Accumulation of Interfacial Charge in Photoconductor-Dielectric Systems

This paper presents experimental results which reveal the occurrence of free-carrier accumlation (i.e., no trapping and no potential-energy barrier to injection) at a photoconductor-dielectric interface. The space-charge-limited current of the dielectric emerges as a key parameter in the process. Several predictions concerning the rate of accumulation of free charge at the interface and the dependence of that rate on applied voltage and current levels in the photoconductor are made using a qualitative model. The experiments were carried out on a model system, amorphous-Se—PVK [poly ($N-\mathrm{v}\mathrm{i}\mathrm{n}\mathrm{y}\mathrm{l}\mathrm{c}\mathrm{a}\mathrm{r}\mathrm{b}\mathrm{a}\mathrm{z}\mathrm{o}\mathrm{l}\mathrm{e}$)], where by means of light the Se is made a conductor of variable "dark" conductance. Direct observation of the development of interfacial charge has been possible by use of a double-relay technique. The variation with applied voltage and light intensity of the time for accumulation of a $CV$ of charge conforms qualitatively with the predictions of the theoretical model.