Tomokazu Umeyama

This review article deals with recent advancements on the application of carbon nanotubes, especially single-walled carbon nanotubes (SWNTs), to a photoactive layer on electrodes of photoelectrochemical devices and cells using liquid electrolytes. Versatile methodologies such as electrophoretic deposition, layer-by-layer deposition, self-assembled monolayer technique, and spray-coating have been adopted to form films of SWNTs on semiconducting or metallic electrodes. In the photoelectrochemical

Solar energy conversion is one of the most important issues for creating and maintaining a future sustainable society. In this regard, photovoltaic technologies have attracted much attention because of their potential to solve energy and environmental issues. In particular, thin-film solar cells, such as organic photovoltaics (OPVs) and perovskite solar cells (PSCs), are highly promising owing to their flexibility, light weight, and low-cost production. One of the most important factors used to

Conjugated polymers with alternating main chain structures of zinc porphyrin−furan (PZnPF) and zinc porphyrin−thiophene (PZnPT) have been synthesized by palladium(0)-catalyzed Stille coupling reaction. The optical, electrochemical, photophysical, and photovoltaic properties of PZnPF and PZnPT were investigated to elucidate the effects of the heterole bridges (i.e., furan vs. thiophene) in the porphyrin polymers. The optical bandgap of PZnPF (1.75 eV) is smaller than that of PZnPT (1.90 eV), impl

Zero-, one-, and two-dimensional nanostructured carbon allotropes, i.e., fullerenes, single-walled carbon nanotubes (SWNTs), and graphenes, in combination with electron-donating conjugated molecules are promising building blocks for artificial photosynthesis and solar energy conversion. This feature article focuses on the fundamental aspects of covalently linked composites of porphyrins with fullerenes, SWNTs, and graphenes. The linkage structures between the porphyrin and nanocarbons have been

Sidewalls of acid-treated, shortened single-walled carbon nanotubes (SWNTs) with long alkyl chains at the open ends and defect sites have been functionalized by Bingel reaction to examine the structures and spectroscopic properties in detail for the first time. The microwave-assisted Bingel reaction has been successfully applied to the sidewall functionalization of which the reaction rate is ca. 50 times faster than that under the conventional conditions. The degree of the sidewall functionaliza

Development of unique conjugated polymer donors, next-generation fullerene acceptors, and one-dimensionally confined, organic donor–acceptor heterojunction nanorods for photovoltaic applications.

Single-walled carbon nanotubes (SWNTs) covalently modified with large porphyrin molecules have been prepared to construct photoelectrochemical devices with nanostructured SnO2 electrodes on which the multiporphyrin-linked SWNTs are deposited electrophoretically. The film of the porphyrin-linked SWNTs on the nanostructured SnO2 electrode exhibited an incident photon-to-photocurrent efficiency as high as 4.9% under an applied potential of 0.08 V vs SCE. The more uniform film and moderate photocurr

Chemically converted graphene (CCG) covalently linked with porphyrins has been prepared by a Suzuki coupling reaction between iodophenyl-functionalized CCG and porphyrin boronic ester. The covalently linked CCG-porphyrin composite was designed to possess a short, rigid phenylene spacer between the porphyrin and the CCG. The composite material formed stable dispersions in DMF and the structure was characterized by spectroscopic, thermal, and microscopic measurements. In steady-state photoluminesc

Electron-acceptor small-molecules possessing a long exciton lifetime and a narrow energy band gap, opposing the energy gap law, are highly desirable for high-performance organic photovoltaics (OPVs) by realizing their efficient light-harvesting ability (LH), exciton diffusion (ED), and charge transfer (CT). Toward this goal, we designed an acceptor-donor-acceptor (A-D-A) type nonfullerene acceptor (NFA), TACIC, having an electron-donating, self-assembling two-dimensional (2D) nanographene unit,

We have successfully developed a new methodology for the self-organization of C(60) molecules on the sidewall of carbon nanotubes for use in photoelectrochemical devices. Novel nanocarbon composites of fullerene (e.g., C(60)) and highly soluble, chemically functionalized single-walled carbon nanotubes (f-SWNT) have been prepared by the rapid injection of a poor solvent (e.g., acetonitrile) into a mixed solution of C(60) and f-SWNT in o-dichlorobenzene. Measurements by using scanning electron mic

To investigate the effect of fluorine substitution on molecular and film structures, optical, electrochemical, and photovoltaic properties of a moderate bandgap polymer, poly(2,7-carbazole-alt-dithienylbenzothiadiazole) (PCDTBT) with deep HOMO energy level, a fluorinated analogue of PCDTBT (i.e., PCDTBT-F) has been developed for the first time by replacing two hydrogen atoms on benzothiadiazole (BT) units with two fluorine atoms. An analogous polymer, PCBBBT-F with additional hexylthiophenes bet

Despite numerous organic semiconductors being developed during the past decade, C₇₀ derivatives are predominantly used as electron acceptors in efficient polymer solar cells (PSCs). However, as-prepared C₇₀ mono-adducts intrinsically comprise regioisomers that would mask individual device performances depending on the substituent position on C₇₀. Herein, we separate the regioisomers of C₇₀ mono-adducts for PSC applications for the first time. Systemati

Photo- and thermal-responsive polymers containing azobenzene units in the main chain have been utilized as removable dispersants for single-walled carbon nanotubes (SWNTs) in organic solvents. Intermolecular interactions between SWNTs and the polymers are reversibly controllable by tuning the trans-cis composition.