Toru Kyomen

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.

Photoinduced insulator-metal transition in Pr0.5Ca0.5CoO3 as studied by femtosecond spectroscopy

Ultrafast optical response has been investigated using fs laser system on a perovskite-type cobalt oxide, Pr0.5Ca0.5CoO3 which undergoes the insulator-metal transition at 89 K. After the photo-irradiation at 30 K, the reflectivity shows a sudden increase. The ultrafast reflectance changes are quantitatively reproduced by the numerical calculation considering the linear combination of the dielectric functions of the initial insulating and the final metallic state, indicating ultrafast phase transition on the time scale of femtosecond.

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.

Photoluminescence and Electroluminescence Properties of (Ca,Sr)TiO3:Er

Powder samples of (Ca,Sr)TiO3:Er were prepared by a solid-state reaction method. Photoluminescence due to f-f transitions of Er3+ was not induced by band-gap excitation of (Ca,Sr)TiO3 but by f-f transitions of Er3+. An electroluminescent device in which thin films of Ca0.6Sr0.4TiO3:Er and SnO2:Sb are stacked alternately was prepared by sol-gel and spin-coating methods. Very weak electroluminescence due to f-f transition of Er3+ was observed in the device.

Electroluminescence of a Multilayer in which Thin Films of NaNbO3:Pr Phosphor and SnO2:Sb Transparent Conductor Are Alternately Stacked

Oxide inorganic electroluminescent device in which thin films of Pr-doped NaNbO3 phosphor and Sb-doped SnO2 transparent conductor are alternately stacked was prepared by sol-gel and spin-coating methods. Red electroluminescence was observed due to f-f transitions of Pr3+ ions by applying 5-kHz ac voltages to the device. The luminance was 1.0 cd m−2 at 25 V ac and5.0 cd m−2 at 34 V ac.

Effect of B2O3 or SiO2 Fluxes on Morphology and Size of Pr-Doped CaTiO3 Phosphor Particles and on their Photoluminescence Properties

Powder of Pr-doped CaTiO3 red phosphor was prepared at 1473 K by a conventional solid-state reaction method with addition of B2O3 or SiO2 as a flux. Primary particle sizes of the prepared samples were increased by using B2O3 flux but decreased by using SiO2 flux. Clear planes, edges, or steps were observed on surfaces of the primary particles. The intensity of photoluminescence induced by irradiation of light with a wavelength longer than ∼350 nm was enhanced about three times by using B2O3 flux. The intensity of photoluminescence induced by irradiation of light with a wavelength shorter than ∼350 nm was enhanced about twice by using either B2O3 or SiO2 fluxes. The origin for the flux effects is discussed.

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.