Improved Routes to Nanocrystalline Metal Oxide Films for Dye-Sensitised Solar Cells and Related Applications

Abstract

Nanoporous metal oxide thin films are currently attracting interest for a wide range of electronic applications, including sensors and dye-sensitised photovoltaic cells. However, limited, and poorly controlled, film fabrication routes represent a key factor impeding the development of such devices. To date, device applications have largely been limited to sol-gelfabricated nanocrystalline films of titanium dioxide (TiO₂). Such studies have recently been extended to the application of an alternative film fabrication technique, notably that of chemical bath deposition (CBD), for the growth of zinc oxide (ZnO). One interesting feature of CBDfabricated films of ZnO is that, under specific conditions of supersaturation, highly reticulated layers may be obtained, such an observation suggesting that control of morphology is possible. Thick nanoporous films of ZnO have been deposited, upon conducting glass substrates, under both acidic and alkaline conditions, from a solution containing the metal ion, added acid or base, and either a chelating agent, such as ethylenediamine or triethanolamine, or a buffer, hexamethylenetetraamine (HMT). The deposition rate is controlled by systematic adjustment of both temperature and pH, together with the nature, and relative concentration, of the reactants in the solution (chelating agent or metal ion). The material properties of the resulting films have been characterised through the use of a range of techniques, including Scanning Electron Microscopy (SEM), X-Ray Powder Diffraction (XRD) and Energy Dispersive Analysis by XRays (EDAX), and the results are discussed within the context of the suitability of the deposited films for incorporation within nanocrystalline devices.