Charge transport on vertically aligned ZnO nanorods with different aspect ratios

Abstract

Zinc Oxide is a semiconductor widely used in sensitized solar cells as an electron transport layer. Among the different nanostructures obtainable for this material, the vertically-aligned ZnO nanorods are of great interest for the design of photoanodes; mainly due to the directionality of charge transport. Vertically-aligned ZnO nanorods of different aspect ratios were prepared via hydrothermal synthesis. UV–Vis absorption was used to determine the dependence of the optical band gap energy on the nanorod diameter according to the Burstein-Moss shift theory due to the presence of surface states. Information about the electronic properties of the different nanorods was obtained by spectroelectrochemical measurements used to monitor the absorbance decrease and Egap shift at different potentials. Time of flight photocurrent transients indicated a dependence on charge transport time with ZnO nanorod length. All evidences point to a large distribution of trap states located in the semiconductor band gap.