Masahiro Hiramoto

Three‐layered organic solar cell with a photoactive interlayer of codeposited pigments

Three‐layered organic solar cell with an interlayer of codeposited pigments of n‐type perylene tetracarboxylic derivative (Me‐PTC) and p‐type metal‐free phthalocyanine (H2Pc) in between the respective pigment layers, was fabricated. Two times larger photocurrent compared to the double‐layered cell without an interlayer was obtained due to the efficient carrier photogeneration in a codeposited layer. The power conversion efficiency reached 0.7% under the intense white light of 100 mW cm−2.

Electrochemical Reduction of Carbon Dioxide on Various Metal Electrodes in Low‐Temperature Aqueous KHCO 3 Media

Electrochemical reduction was investigated on 32 metal electrodes in aqueous medium. The current efficiency of reduction on Ni, Ag, Pb, and Pd increases significantly with lowering the temperature. The ratio of reduction products are also changed by lowering temperature. Potential dependence of and on an Hg electrode supports the electron transfer mechanism for production. Formation of methane and ethylene is observed on almost all metal electrodes used, although the efficiency is mainly very low except for Cu. A periodic table for reduction, which is drawn based on the dependence of reduction products on various metals, suggests the existence of a systematic rule for the electrocatalytic reduction of on metal surfaces.

p‐i‐n like behavior in three‐layered organic solar cells having a co‐deposited interlayer of pigments

Three‐layered organic solar cells, having a sandwiched interlayer of co‐deposited p‐type phthalocyanine (Pc) pigments and n‐type perylene derivative (PTC) pigments, exhibited photocurrent enhancement when compared with two‐layered cells without the interlayer. A large number of Pc/PTC molecular contacts within the interlayer serve as active sites for effective charge carrier photogeneration. The photovoltaic characteristics of the three‐layered configuration suggest the formation of a p‐i‐n like structure, in which the built‐in potential produced by Fermi level differences in the respective pigment layers is mainly distributed across the co‐deposited interlayer. Inorganic semiconductor films are also shown to be applicable to the present p‐i‐n cell structure as an n layer to obtain larger photovoltages.

Conjugated organic framework with three-dimensionally ordered stable structure and delocalized π clouds

Covalent organic frameworks are a class of crystalline organic porous materials that can utilize π–π-stacking interactions as a driving force for the crystallization of polygonal sheets to form layered frameworks and ordered pores. However, typical examples are chemically unstable and lack intrasheet π-conjugation, thereby significantly limiting their applications. Here we report a chemically stable, electronically conjugated organic framework with topologically designed wire frameworks and open nanochannels, in which the π conjugation-spans the two-dimensional sheets. Our framework permits inborn periodic ordering of conjugated chains in all three dimensions and exhibits a striking combination of properties: chemical stability, extended π-delocalization, ability to host guest molecules and hole mobility. We show that the π-conjugated organic framework is useful for high on-off ratio photoswitches and photovoltaic cells. Therefore, this strategy may constitute a step towards realizing ordered semiconducting porous materials for innovations based on two-dimensionally extended π systems.

Photocurrent multiplication in organic pigment films

Large photocurrent multiplication reaching 10 000 times has been observed in a perylene pigment film sandwiched between Au electrodes. The phenomenon occurs at the interface between the perylene film and a negatively biased Au electrode and is found to be associated with electron injection from the Au electrode to the perylene film through the depletion layer formed in the pigment film under a high electric field, which is built up by the photoaccumulated space charges of trapped holes near the interface.

Three-layered organic solar cells incorporating a nanostructure-optimized phthalocyanine:fullerene codeposited interlayer

Three-layered organic solar cells incorporating a codeposited interlayer of fullerene and metal-free phthalocyanine, whose nanostructure was optimized by controlling the substrate temperature during coevaporation, showed a photoelectric conversion efficiency of 2.5% under illumination with simulated solar light. The three-layered cells were concluded to have a p-i-n-like energetic structure.

Efficient Organic p-i-n Solar Cells Having Very Thick Codeposited i-Layer Consisting of Highly Purified Organic Semiconductors

p-i-n organic solar cells having very thick codeposited i-interlayer reaching 1.2 μm were successfully fabricated by using fullerene purified by means of the single-crystal formed sublimation. Short-circuit photocurrent density of 19 mAcm−2 and photo-electric conversion efficiency of 5.3% were observed.

Organic solar cells protected by very thick naphthalene tetracarboxylic anhydride films

The insertion of very thick naphthalene tetracarboxylic anhydride films under vacuum-deposited metal electrodes effectively protected pn-heterojunction organic solar cells from shorting-out electrically. Fill-factors of 0.56 and conversion efficiencies (corrected for absorbed light) of 3.07% were observed. The present technique would be a powerful tool for the fabrication of large area organic solar cells.

Photoelectrolysis of Water under Visible Light with Doped SrTiO3 Electrodes

Etudes du comportement photoelectrochimique des electrodes de SrTiO 3 dopees avec divers oxydes metalliques (RuO 2 , CoO, Ce 2 O 3 , Cr 2 O 3 , etc.), en solution aqueuse

Conduction-type control of fullerene films from n- to p-type by molybdenum oxide doping

Conduction-type control of fullerene (C60) films from n- to p-type by doping with molybdenum oxide (MoO3) was demonstrated. The energetic value of the Fermi level, 4.60 eV, for nondoped C60 films measured by the Kelvin vibrating capacitor method was positively shifted to 5.88 eV, and approached the valence band by the coevaporated doping of MoO3 at a concentration of 3300 ppm. The existence of upward band bending of the Schottky junction formed at the interface between a metal and a p-type C60 film formed by MoO3 doping was confirmed based on its photovoltaic properties.