Kenji Kakiage

Achievement of over 1.4 V photovoltage in a dye-sensitized solar cell by the application of a silyl-anchor coumarin dye

A dye-sensitized solar cell (DSSC) fabricated by using a novel silyl-anchor coumarin dye with alkyl-chain substitutes, a Br3−/Br− redox electrolyte solution containing water, and a Mg2+-doped anatase-TiO2 electrode with twofold surface modification by MgO and Al2O3 exhibited an open-circuit photovoltage over 1.4 V, demonstrating the possibility of DSSCs as practical photovoltaic devices.

A Novel Alkoxysilyl Azobenzene Dye Photosensitizer with Alkylamino Group for Dye-Sensitized Solar Cells

A newly designed alkoxysilyl azobenzene dye with alkylamino group, 4-diethoxyphenylsilyl-4′-dimethylaminoazobenzene, was synthesized and examined as the photosensitizer for a dye-sensitized solar cell (DSSC). The novel azobenzene dye exhibited a strong absorption band in the visible region, and the solar cell using the dye as the sensitizer showed an incident monochromatic photon-to-current conversion efficiency (IPCE) value of 66 % at 440 nm and a light-to-electric energy conversion efficiency of 2.2 % under simulated sunlight irradiation of AM-1.5G one sun condition. The energy conversion efficiency obtained here is the highest value among those reported so far for azobenzene-sensitized solar cells, indicating the potential of alkoxysilyl dyes as photosensitizers for DSSCs.

Adsorption and Sensitizing Properties of Azobenzenes Having Different Numbers of Silyl-Anchor Groups in Dye-Sensitized Solar Cells

The effects of the silyl-anchor group number on the adsorption and the sensitizing properties were examined in sensitizing dyes for dye-sensitized solar cells by using 4-alkoxysilyl and 2,4-dialkoxysilyl azobenzenes. The TiO2 electrode with the 2,4-disilyl dye exhibited higher durability to water and better photovoltaic performance than that with the 4-monosilyl dye, although the amount of 2,4-disilyl dye molecules adsorbed on the TiO2 electrode was slightly smaller than in the case of 4-monosilyl dye.

Improvement of Photovoltage in Dye-Sensitized Solar Cells with Azobenzene and Azulene Sensitizing Dyes by Applying Br3-/Br- Redox Mediator

In dye-sensitized solar cells (DSSCs) fabricated with azobenzene and azulene derivatives as the photosensitizing dyes, the replacement of the conventional I3-/I- redox mediator with Br3-/Br- redox mediator possessing more positive redox potential has been examined to improve open-circuit photovoltages (Voc) of the cells. The cells with the Br3-/Br- redox mediator exhibited high Voc of ~0.8 V, resulting in higher light-to-electric energy conversion efficiencies (η) than the cells with the I3-/I- redox mediator by a factor of 1.7 under the simulated sunlight irradiation (AM-1.5G, 100 mW cm-2). The results indicate a high potential of the Br3-/Br- redox mediator in DSSCs.

Effect of the Introduction of a CF3 Group to a Silyl-Anchor Azobenzene Dye on Sensitization Property in Dye-Sensitized Solar Cells

The effect of the introduction of a CF3 group to a silyl-anchor moiety of the sensitizer on the sensitizing property for the dye-sensitized solar cell was examined by using alkoxysilyl-anchor azobenzene dyes. The cell sensitized by the silyl-anchor dye with the electron-withdrawing CF3 group in the silyl-anchor moiety exhibited higher photovoltaic performance than that by the silyl-anchor dye without the CF3 group.

Study of Allylsilyl and Hydrosilyl Groups as Anchor Moieties of Sensitizing Dyes for Dye-Sensitized Solar Cells

Allylsilyl and hydrosilyl groups were examined as the anchor moieties of sensitizing dyes for dye-sensitized solar cells by using silylazobenzene dyes. Allylsilyl and hydrosilyl dyes were observed to adsorb efficiently onto TiO2 electrodes and the dye-adsorbed electrodes exhibited high durability to water. Light-to-electric energy conversions were also confirmed in the cells using the dye-adsorbed electrodes. The results show a high potential of allylsilyl and hydrosilyl dyes as the sensitizing dyes.

Structural Properties of SrTiO3 Transparent Thin Films Formed by RF Magnetron Sputtering with Changing Substrate Temperatures

Transparent thin films of strontium titanate (SrTiO3) were formed on the substrate of quartz glass plate by RF magnetron sputtering with changing the substrate temperatures during the sputtering from 100 to 700 °C. The particle size and the lattice constant of the cubic-SrTiO3 crystallites composing the film were exhibited to be changed from 13 to 48 nm and from 4.02 to 3.96 Å, respectively, by the change of the substrate temperatures from 400 to 700 °C. The UV absorption edges of the transparent film samples shifted to longer wavelength with the increase of the particle size and the decrease of the lattice constant of the nanocrystalline SrTiO3.

Study of the Chemical Adsorption Property of Allylsilylazobenzene in the Surface Modification of Nanoporous Alumina Membrane

In order to clarify the chemical adsorption property of allylsilane to metal-oxide surface quantitatively and to obtain the information on the reaction conditions for the efficient surface modification, chemical surface modification of nanoporous alumina membranes (NPAMs) by a typical allylsilyl compound of 4-(allyldimethylsilyl) azobenzene was examined. The chemical surface modification was performed by immersing NPAMs into the solutions of the allylsilylazobenzene. The modification was investigated precisely by estimating the amount of the silylazobenzene adsorbed on the NPAM surface using a visible absorption spectroscopy with changing the temperature, solvent, and the concentration of the solution to reveal the effects of the reaction conditions on the adsorption property of the allylsilane to the metal-oxide surface. The solutions with higher temperatures, non-polar solvents, and higher concentrations were shown to be suitable for the efficient surface modification.

Application of Micro-Metal Textile for Flexible Dye-Sensitized Solar Cell

As a means to make a flexible dye-sensitized solar cell (DSSC), we prepared a TiO2 electrode by using a micro-metal textile made from Sn-plated Cu wires, and examined applicability of the micro-metal textile as a substrate for the electrode. The TiO2 electrodes were prepared successfully by painting a TiO2 paste to the textile using a squeegee method followed by sintering at 500 °C, and the electrodes showed no exfoliation of the TiO2 layer from the textile even when the electrode was bent to a cylindrical shape with 10-mm diameter. The solar cells constructed with these electrodes, on which N3 dye was adsorbed as a sensitizer, exhibited actually a photovoltaic performance. The results indicated the applicability of the micro-metal textile as the flexible substrate for the TiO2 electrode producing an efficient flexible DSSC.