Ryo Kawakami

Evaluation of TiO2 Nanoparticle Thin Films Prepared by Electrophoresis Deposition

The absence of cracks and a high optical transparency are critical factors for obtaining high performance when TiO2 thin films are used as photocatalysts and as the cathode material in dye-sensitized solar cells. Synthesized TiO2 nanoparticles were deposited by constant-current electrophoresis in ethanol. TiO2 nanoparticle thin films deposited at a low current density had no apparent cracks and a high optical transparency. Small TiO2 nanoparticles deposited are thought to be transported at low current densities. This enables TiO2 nanoparticle chains to form by the oriented attachment mechanism and thereby increases the electron diffusion length.

Preparation and Evaluation of TiO2 Nanoparticle Thin Films using Electrophoresis Deposition Method

Thin films of synthesized TiO2 nanoparticles were deposited by constant-current electrophoresis deposition in ethanol using colloid of various concentration of TiO2 nanoparticles. Thin films deposited in colloid of high concentration had the high density, no apparent cracks and the higher optical transparency. The eficiency of the fabricated dye-sensitized solar cells was improved using thin film of TiO2 nanoparticle deposited in colloid with high concentration. It was suggested that the thin film with high quality could be deposited by making the velocity of a TiO2 nanoparticle low because the linkage between TiO2 nanoparticles were promoted by oriented attachment mechanism.

Evaluation of TiO2 Nanotube Thin Films Fabricated by Anodic Oxidation

Titanium dioxide nanotubes (TNTs) were grown by anodic oxidation of a titanium thin film deposited on an indium tin oxide (ITO) glass substrate. The TNTs were arranged densely and formed a thin film on the ITO substrate. Anodic oxidation was carried out at 550oC in an electrolyte. The inner diameter and tube length of a grown TNT were approximately 15 nm and 0.5 μm, respectively. Several of the TNT tube openings were closed by lids. These lids could be removed by sputter etching for a short time. The crystal structure was non-crystalline. The power conversion efficiency of a dye sensitized solar cell fabricated using the TNT thin film as a negative electrode is much smaller than that fabricated using conventional TiO2 nanoparticle thin films, at present.

Fabrication and Evaluation of Titanium Dioxide Nanotube Thin Films by Anodic Oxidation on Transparent Electrodes

Titanium dioxide nanotube (TNT) thin films were fabricated, for application as the negative electrode of dye-sensitized solar cells (DSC), by anodic oxidation of titanium thin films deposited by RF magnetron sputtering on indium tin oxide glass substrates. Anodic oxidation was carried out by a constant voltage or constant current method in an electrolyte in order to determine the best method to increase TNT film thickness. Thick titanium dioxide films were fabricated by the constant voltage method at higher voltages. Thicker titanium dioxide films were obtained by the constant current method compared to the constant voltage method. However, the constant current method with optimal current yielded TNT films with higher quality (high transparency). The power conversion efficiency of DSC was improved using films fabricated by the constant current method.

Effects of Particle Size on Properties of TiO2 Nanoparticle Thin Films Deposited by Electrophoresis

The absence of cracks and a high optical transparency are critical factors for obtaining high performance when TiO2 thin films are used as cathodes in dye-sensitized solar cells (DSSCs). Synthesized and classified TiO2 nanoparticles were deposited by constant-current electrophoresis in ethanol. The optical transparency of thin films and the DSSC efficiency increased rapidly with decreasing particle size and increasing film homogeneity. This increase in the DSSC efficiency suggests that the electron conduction path in a thin film consists of connections in the crystal lattice formed between TiO2 nanoparticles. This formation of connections increases the electron diffusion length.