Titania Nanoparticle Film Prepared by Electrophoretic Deposition under DC Constant-Current Condition

Abstract

Electrophoretic deposition (EPD) is one of useful methods for the preparation of the thin film with homogeneous microstructure on a conductive substrate. In the EPD method, the structure of the particle thin film could be controlled by adjusting the electrical operating conditions. Titania nanoparticle (NP) films, which are used for the electrode of dye-sensitized solar cells (DSSCs), require not only the homogeneous microstructure but also controlled pore size distribution, contributing to high-rate transport of electrons for the high conversion efficiency of DSSCs. In this study, titania NP films were prepared by EPD under DC constant-current conditions using available NPs dispersed in ethanol. The thickness as well as the weight of the titania NP film appeared to be increased almost linearly with EPD operation time, while the porosity of the film calculated from those values was not always constant but increased slightly with the operation time and asymptotically reached about 60%. We confirmed that the forces on the particles depositing onto the substrate became weaker as the EPD operation time increased, due to the electrostatic charges gradually building up on the thin NP film with particle deposition. The deposition behavior of titania NPs was drastically changed upon varying the water content in ethanol. We detected many pinholes on the surface of thin NP films when the water content in ethanol increased. The amount of particles accumulated on the substrate via EPD could be calculated based on the electrical conductivity of the suspension and the mobility of particles in the suspension, but was found to be underestimated when the water content increased.