Abstract
Electrophoretic deposition (EPD) is advantageous in preparing thin films, consisting of nanoparticles (NPs), with homogeneous microstructure on a conductive substrate of little restriction to its geometry. This film- preparation technique could play a significant role in improving, by properly structuring the film in terms of its thickness and porosity, the performance of electrode of dye-sensitized solar cells (DSSCs). In this study, we attempted to prepare thin films of titania NPs by applying EPD from non-aqueous suspensions and discussed the effects of water content of suspension, particle size, particle shape and the type of solvent on the structure of thin film. When the commercial product (P-25, Evonik, 21-nm primary particle size) was used, the deposition weight of particles from the ethanol suspension linearly increased with applied EPD time, and was found to be estimated by the Hamaker equation. The water content in the suspension did not affect the structure of the thin film characterized by its weight, thickness and porosity. When the particle size was controlled by applying a milling operation, the porosity of deposition layer increased with particle size over a certain thickness range of deposition layer, although the deposition rate did not depend on the particle size. When the rod-like NPs (HPW-18NR, JGC C&C, 20-nm primary particle size) were used instead of round P-25 NPs, the deposition rate of HPW-18NR NPs became lower than that of P-25 NPs, as in the case of the porosity of the deposition layer of HPW-18NR NPs. When P-25 NPs suspended in a mixture solvent of ethanol and t-butyl alcohol (2-methyl-2-propanol) were tested for EPD, the structure of the deposited thin film depended on the mixture composition ratio.
