Dye-sensitization mechanism of zinc oxide thin layers

Thin layers of zinc oxide, prepared by oxidizing zinc selenide were used to examine a previously proposed model for the spectral sensitization of photoconduction. When the sensitizing dyes were adsorbed in low densities, the chemical interactions between the dyes and zinc oxide seemed to repopulate the surface-trapped electrons and the population determined the sensitizing efficiency. When dyes were densely adsorbed, however, the trapping effect by dye molecules appeared to be large enough to smear the primary chemical interactions with zinc oxide. In dyes of a similar chemical structure, the sensitizing efficiency was related to the saturation value for dye adsorption. The light intensity dependence of photocurrent was observed to be varied by the adsorption density of dyes, reflecting the influence of trapping.