Moltipod-like zinc oxide nanostructures as photoanodes in Dye-sensitized Solar Cells

Zinc oxide is a well known material for Dye-sensitized Solar Cell (DSC) application, being an interesting alternative to the most commonly used titanium dioxide. ZnO is a wide band gap semiconductor with a conduction band edge positioned approximately at the same level as in TiO2, meaning that ruthenium-based dyes developed for TiO2 can efficiently work also when linked to ZnO. With respect to titanium dioxide, ZnO presents higher electron mobility and longer carrier lifetime, being these parameters very important in the fabrication of efficient DSC photoanodes. Moreover, zinc oxide is well known for its ability to easily grow in a wide variety of nanostructures, like nanoparticles, nanowires or nanorods, nanotubes, nanosheets, nanoplants and nanotetrapods, just to cite some valuable examples. In this work, we propose the fabrication and characterization of DSCs exploiting multipod ZnO-based photoanodes. The shape-controlled synthesis of these ZnO microparticles was carried out by simple hydrothermal process through the reaction of zinc acetate salts with potassium hydroxide. Mild reaction conditions were used (70 °C) and wurtzite-like crystalline structure readily obtained after the reaction process. After dispersion of ZnO nanostructures in acetic acid-based solution, a 18 μm-thick ZnO layer acting as DSC photoanode was obtained. With the goal of obtaining high efficiency from the cells fabricated with these nanostructured photoanodes, we carried out the optimization of the experimental conditions (dye immersion time, sensitizing solution pH, dye concentration) by means of response surface methodology (RSM), a collection of statistical and mathematical techniques useful for developing, refining and improving products and processes.