Control of Nanostructure and Crystallographic Orientation in Electrodeposited ZnO Thin Films via Structure Directing Agents

The nanostructure and crystallographic orientation of ZnO thin films were controlled by using structure directing agents (SDAs) in the electrodeposition from O-2-saturated ZnCl2 aqueous solutions. While hybrid thin film with eosin Y (ZnOEY) has a nanoporous structure oriented with the c-axis-in perpendicular to the substrate, that with citric acid (ZnOCA) was found to have a contrasting lamellar structure consisting of stacked platelets of ZnO and oriented with its c-axis in parallel with the substrate. We show that switching of the SDA from CA to EY during the course of electrodeposition of a film changes the nanostructure but preserves crystal orientation. We propose a mechanism whereby the SDA can define crystallographic Orientation from the randomly oriented seed layer. However once the orientation is defined, it is maintained by homoepitaxial growth of ZnO crystallites and the SDA will define only the morphology. This way, bilayer ZnO films with totally different crystallographic orientation but almost identical nanostructure were prepared. Dye-sensitized solar cells employing these films were used to investigate the influence of the c-axis orientation on the efficiency of electron injection recombination. (C) 2014 The Electrochemical Society. All rights reserved.