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Seiji Isoda

Publications and source records attributed to Seiji Isoda.

11 recordsLinked to original sources
PubMed2006

Determination of parameters of electron transport in dye-sensitized solar cells using electrochemical impedance spectroscopy.

The same equation was derived from two different impedance models based on the quite different physical descriptions proposed by Kern et al.(1) and by Bisquert.(2,3) Reliable values of the parameters relating to electron transport in dye-sensitized solar cells can be determined from measured spectra by electrochemical impedance spectroscopy when careful analysis of the measured spectra is done based on the classification and clarification of the same impedance equation consequent from the two models. The requisites for making highly efficient dye-sensitized solar cells were proposed.

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PubMed2006

A photoelectrochemical device with a nanostructured SnO2 electrode modified with composite clusters of porphyrin-modified silica nanoparticle and fullerene.

A silica nanoparticle has been successfully employed as a nanoscaffold to self-organize porphyrin and C60 molecules on a nanostructured SnO2 electrode. The quenching of the porphyrin excited singlet state on the silica nanoparticle is suppressed significantly, showing that silica nanoparticles are promising scaffolds for organizing photoactive molecules three-dimensionally in nanometer scale. Marked enhancement of the photocurrent generation was achieved in the present system compared with the reference system, where a gold core was employed as a scaffold of porphyrins instead of a silica nanoparticle. The rather small incident photon-to-current efficiency relative to a similar photoelectrochemical device using a silica microparticle may result from poor electron and hole mobility in the composite film due to poor connection between the composite clusters of a porphyrin-modified silica nanoparticle and C60 in micrometer scale.

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PubMed2006

Structure and photoelectrochemical properties of phthalocyanine and perylene diimide composite clusters deposited electrophoretically on nanostructured SnO2 electrodes.

Clusters of phthalocyanine and phthalocyanine-perylene diimide have been prepared and electrophoretically deposited on nanostructured SnO2 electrodes. The structure and photoelectrochemical properties of the clusters have been investigated by using UV-visible absorption, dynamic light scattering (DLS), atomic force microscopy (AFM), transmission electron microscopy (TEM), and photoelectrochemical and photodynamical measurements. Enhancement of the photocurrent generation efficiency in the composite system has been achieved relative to that in the phthalocyanine reference system without the perylene diimide. Such information will be valuable for the design of molecular photoelectrochemical devices that exhibit efficient photocurrent generation.

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PubMed2006

Dye-sensitized solar cells based on a single-crystalline TiO2 nanorod film.

Highly crystalline TiO2 nanorods with lengths of 100-300 nm and diameters of 20-30 nm have been synthesized by a hydrothermal process in a cetyltrimethylammonium bromide surfactant solution. The microstructure measured by X-ray diffraction and high-resolution transmission electron microscopy was a pure highly crystalline anatase phase with a long nanorod shape. The addition of a triblock copolymer poly(ethylene oxide)100-poly(propylene oxide) 65-poly(ethylene oxide)100 (F127) decreased the length of the nanorods and kept the rod shape of the particles even after sintering at high temperatures. The rod shape kept under high calcination temperatures contributed to the achievement of the high conversion efficiency of light-to-electricity as discussed in the paper. A high conversion efficiency of light-to-electricity of 7.29% was obtained with the TiO2 single-crystalline anatase nanorod cell.

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PubMed2005

Host-guest interactions in the supramolecular incorporation of fullerenes into tailored holes on porphyrin-modified gold nanoparticles in molecular photovoltaics.

Novel gold nanoparticles modified with a mixed self-assembled monolayer of porphyrin alkanethiol and short-chain alkanethiol were prepared (first step) to examine the size and shape effects of surface holes (host) on porphyrin-modified gold nanoparticles. The porphyrin-modified gold nanoparticles with a size of about 10 nm incorporated C60 molecules (guest) into the large, bucket-shaped holes, leading to the formation of a supramolecular complex of porphyrin-C60 composites (second step). Large composite clusters with a size of 200-400 nm were grown from the supramolecular complex of porphyrin-C60 composites in mixed solvents (third step) and deposited electrophoretically onto nanostructured SnO2 electrodes (fourth step). Differences in the porphyrin:C60 ratio were found to affect the structures and photoelectrochemical properties of the composite clusters in mixed solvents as well as on the SnO2 electrodes. The photoelectrochemical performance of a photoelectrochemical device consisting of SnO2 electrodes modified with the porphyrin-C60 composites was enhanced relative to a reference system with small, wedged-shaped surface holes on the gold nanoparticle. Time-resolved transient absorption spectroscopy with fluorescence lifetime measurements suggest the occurrence of ultrafast electron transfer from the porphyrin excited singlet states to C60 or the formation of a partial charge-transfer state in the composite clusters of supramolecular complexes formed between porphyrin and C60 leading to efficient photocurrent generation in the system. Elucidation of the relationship between host-guest interactions and photoelectrochemical function in the present system will provide valuable information on the design of molecular devices and machines including molecular photovoltaics.

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PubMed2005

Effects of fullerene substituents on structure and photoelectrochemical properties of fullerene nanoclusters electrophoretically deposited on nanostructured SnO2 electrodes.

Two kinds of fullerene derivatives have been designed to examine the effect of the fullerene substituents on the structure and photoelectrochemical properties of fullerene clusters electrophoretically deposited on nanostructured SnO(2) electrodes. The cluster sizes increase and the incident photon-to-current efficiencies decrease with introduction of large substituents into C(60). The trend for photocurrent generation efficiency as well as surface morphology on the electrode can be explained by the steric bulkiness around the C(60) molecules. A C(60) molecule with two alkoxy chains is suggested to give a bilayer vesicle structure, irrespective of the hydrophobic nature of both the C(60) and alkoxy chain moieties. Such information will be valuable for the design of photoactive molecules, which are fabricated onto electrode surfaces to exhibit high energy conversion efficiency.

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PubMed2005

Aggregated structure analysis of polymer-protected platinum/ruthenium colloidal dispersions using EXAFS, HRTEM, and electron diffraction measurements.

Polymer-protected platinum/ruthenium colloidal dispersions were prepared by refluxing mixed solutions of hexachloroplatinic(IV) acid and ruthenium(III) chloride in a mixture of ethanol/water (1/1 v/v) in the presence of poly(N-vinyl-2-pyrrolidone). The electronic spectra and transmission electron micrographs suggested that the colloidal dispersions are almost composed of the mixture of the small monometallic Pt and Ru clusters over all the ratio of Pt/Ru compositions. Extended X-ray absorption fine structure analyses and high resolution electron microprobe analyses indicated that no Pt/Ru alloy clusters exist in the dispersions, and the aggregation occurs between small monometallic Pt clusters (diameter ca. 15 A) and partially oxidized Ru microclusters (diameter less than 10 A). Electron diffraction measurements also suggested that the diffraction pattern of aggregated Pt/Ru cluster particles prepared by the simultaneous reduction of Pt and Ru ions is the same as that of the physical mixture of the small monometallic Pt and Ru clusters separately prepared. Therefore, it can be concluded that the aggregated Pt/Ru cluster particles, with 10 to 60 A in diameter, are built up by small monometallic Pt clusters and partially oxidized Ru microclusters, and that Pt/Ru alloy clusters are not formed.

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PubMed2003

A phthalocyanine dendrimer capable of forming spherical micelles.

A novel and intrinsically spherical micelle has been prepared by utilizing a silicon phthalocyanine ((WG3)SiPc) that has a thin hydrophobic alkyl chain and a bulky hydrophilic poly(aryl ether) dendrimer with terminal carboxyl groups, as its two axial ligands. Gel-permeation chromatography and cryo-transmission electron microscopic experiments indicate that (WG3)SiPcs self-assemble to form a spherical micelle at very low concentrations in aqueous solution. Depending on the pH of the aqueous phase, (WG3)SiPc shuttles between aqueous and organic phases. In the presence of hydrophobic molecules, this transfer is accompanied by the inclusion of these (guest) molecules, indicating that the micelle acts as a molecular capsule with a nanospace surrounded by functional phthalocyanine planes.

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PubMed2003

Inhomogeneous substitution of polyhalogenated copper-phthalocyanine studied by high-resolution imaging and electron crystallography.

The present study was aimed at distinguishing halogen atoms substituted in a molecule of copper-phthalocyanine (CuPc) by high-resolution transmission electron microscopy (HRTEM). The subject was carried out on octabromooctachloro-CuPc and obtained HRTEM images suggested inhomogeneous distribution of bromine and chlorine atoms at 1-, 2-, 3- and 4-substitution positions of CuPc in image contrast. As a result of electron crystallography, the occupancy of bromine atoms at the 1-position (and equally at the 4-position) was found to be 52%, which is slightly higher than for random substitution. This small deviation causes apparent inhomogeneous image contrast of halogen substitution observed in the high-resolution images, as concluded from computer simulation of images. Such potential to detect inhomogeneity in substitution by TEM should be important for the chemical understanding of substitution reactions at the atomic level.

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PubMed2002

TEM observation of lattice plane expansion at the surface of a molecular crystal Br8Cl8-Cu-phthalocyanine.

Generally, structures of molecular crystals have imperfections and are therefore rather complex. One kind of imperfection is an expansion of the distance between molecular planes that occurs near a crystal surface. Although such an expansion is often observed in a high-resolution image, it has not been measured quantitatively because of the low signal-to-noise ratio of such images. This problem is due to the sensitivity of molecular crystals to electron doses. Here, we have taken photographs of a crystal surface under high magnification in so far as the dose does not destroy the crystal structure. We have quantitatively measured the distance expansion based on image processing and statistical analysis of many photographs. As a result, we have confirmed that the first and second molecular planes shift towards the outside of a crystal in sub-angstrom order.

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