Yohei Adachi

Synthesis of D–A polymers with a disilanobithiophene donor and a pyridine or pyrazine acceptor and their applications to dye-sensitized solar cells

New donor–acceptor polymers containing disilanobithiophene (DSBT) as the donor and pyridine or pyrazine as the acceptor with or without a thiophene spacer were prepared. The polymers showed UV-vis absorption maxima at λmax = 488–526 nm, which were red-shifted relative to those of model monomers dithienylpyridine and dithienylpyrazine (λmax = 352–375 nm), indicating the efficient conjugation along the polymer chains. A homo polymer of DSBT was also prepared. The DSBT-containing polymers were attached to TiO2 electrodes by immersing the electrodes in the polymer solutions under irradiation (>400 nm) or in the dark. The modified electrodes were applied to dye-sensitized solar cells and a maximal power conversion efficiency of 0.89% was obtained using the TiO2 electrode thermally modified with a DSBT–pyrazine alternating polymer.

Synthesis, optical and electrochemical properties, and photovoltaic performance of a panchromatic and near-infrared (D)2–π–A type BODIPY dye with pyridyl group or cyanoacrylic acid

(D)2–π–A type boron dipyrromethene (BODIPY) dyes OMK-PY and OMK-CA bearing a pyridyl group or cyanoacrylic acid group, respectively, at the end of 8-positions on the BODIPY core, as an electron-withdrawing anchoring group to adsorb onto the TiO2 electrode and two diphenylamine–thienylcarbazole moieties as an electron-donating unit at the 3- and 5-positions on the BODIPY core, were designed and developed as a photosensitizer for dye-sensitized solar cells (DSSCs). It was found that the two BODIPY dyes adsorbed on a TiO2 film show a strong and broad absorption band in the range of 600 to 850 nm, and the onset of the absorption band reached 900 nm, that is, OMK-PY and OMK-CA possess the near-infrared (NIR) adsorption ability as well as the panchromatic adsorption ability, and good adsorption ability onto the TiO2 electrode. Moreover, cyclic voltammetry demonstrated that the two BODIPY dyes show two reversible oxidation waves, thus indicating that the redox processes of OMK-PY and OMK-CA are very stable. On the basis of the experimental results and density functional theory calculation, we propose that the (D)2–π–A BODIPY structure with two diphenylamine–thienylcarbazole moieties as strong electron-donating units at the 3- and 5-positions on the BODIPY core is an effective strategy to lead a high light-harvesting efficiency (LHE) in the range of visible light to NIR light, although the DSSCs based on (D)2–π–A type BODIPY dyes that have been developed in this current stage showed low photovoltaic performances.

Development of type-I/type-II hybrid dye sensitizer with both pyridyl group and catechol unit as anchoring group for type-I/type-II dye-sensitized solar cell

A type-I/type-II hybrid dye sensitizer with a pyridyl group and a catechol unit as the anchoring group has been developed and its photovoltaic performance in dye-sensitized solar cells (DSSCs) is investigated. The sensitizer has the ability to adsorb on a TiO2 electrode through both the coordination bond at Lewis acid sites and the bidentate binuclear bridging linkage at Brønsted acid sites on the TiO2 surface, which makes it possible to inject an electron into the conduction band of the TiO2 electrode by the intramolecular charge-transfer (ICT) excitation (type-I pathway) and by the photoexcitation of the dye-to-TiO2 charge transfer (DTCT) band (type-II pathway). It was found that the type-I/type-II hybrid dye sensitizer adsorbed on TiO2 film exhibits a broad photoabsorption band originating from ICT and DTCT characteristics. Here we reveal the photophysical and electrochemical properties of the type-I/type-II hybrid dye sensitizer bearing a pyridyl group and a catechol unit, along with its adsorption modes onto TiO2 film, and its photovoltaic performance in type-I/type-II DSSC, based on optical (photoabsorption and fluorescence spectroscopy) and electrochemical measurements (cyclic voltammetry), density functional theory (DFT) calculation, FT-IR spectroscopy of the dyes adsorbed on TiO2 film, photocurrent-voltage (I-V) curves, incident photon-to-current conversion efficiency (IPCE) spectra, and electrochemical impedance spectroscopy (EIS) for DSSC.

Hybrid conjugated polymers with alternating dithienosilole or dithienogermole and tricoordinate boron units

Conjugated polymers composed of tricoordinate boron and π-conjugated units possess extended conjugation with relatively low-lying LUMOs arising from pB–π interactions. However, donor–acceptor (D–A) polymers that feature triorganoboranes alternating with highly electron-rich donors remain scarce. We present here a new class of hybrid D–A polymers that combine electron-rich dithienosiloles or dithienogermoles with highly robust tricoordinate borane acceptors. Polymers of modest to high molecular weight are readily prepared by Pd-catalyzed Stille coupling reaction of bis(halothienyl)boranes and distannyldithienosiloles or -germoles. The polymers are obtained as dark red solids that are stable in air and soluble in common organic solvents. Long wavelength UV-vis absorptions at ca. 500–550 nm indicate effective π-conjugation and pronounced D–A interactions along the backbone. The emission maxima occur at wavelengths longer than 600 nm in solution and experience further shifts to lower energy with increasing solvent polarity, indicative of strong intramolecular charge transfer (ICT) character of the excited state. The powerful acceptor character of the borane comonomer units in the polymer structures is also evident from cyclic voltammetry (CV) analyses that reveal relatively low-lying LUMO levels of the polymers, enhancing the D–A interaction. Density functional theory (DFT) calculations on model oligomers further support these experimental observations.

Hydrophobic modification of SiO2 surface by aminosilane derivatives

Abstract New aminosilanes with hydrolysable Si-N bond(s) were prepared by the amination of chlorosilanes and used as hydrophobic modifiers of SiO2 surface. The aminosilanes are rather stable towards hydrolysis in air compared to their chlorosilane analogs. The modified SiO2 was applied as a gate insulator of an organic thin-film transistor with a vapor-deposited film of pentacene as the active material. The transistor with the aminosilane-modified SiO2 showed two- to threefold higher hole mobility than the device with bare SiO2.

Hydrophobic modification of SiO2 surface with disilanobiphenyl and disilanobithiophene and the application to pentacene-based organic transistors

ABSTRACT Surface modification of inorganic oxide with organic modifiers is an important process in areas of surface and interface engineering. In this paper, we report the hydrophobic modification of SiO2 surface using tetramethyldisilanobiphenyl (DSBP) and tetramethyldisilanobithiophene (DSBT) as new modifiers. Irradiation of an ozone-cleaned glass plate in a toluene solution of DSBP with a low-pressure mercury lamp at room temperature in an argon atmosphere led to the hydrophobic modification of the glass surface. Treatment of a glass plate in the dark at room temperature provided similar hydrophobic surface, although the process proceeded less rapidly. Modification of glass surface was also possible by DSBT, but less effectively. This process with DSBP was applied to the fabrication of the top-contact p-type organic thin film transistor (OTFT) with a pentacene film as the active layer, prepared by vapor-deposition on SiO2/Si surface. Modification of SiO2/Si surface by DSBP led to enhanced mobility, by enlargement of grain size and enhancement of the crystallinity.