Yutaka Harima

Dye-sensitized solar cells based on D-π-A fluorescent dyes with two pyridyl groups as an electron-withdrawing-injecting anchoring group.

D-π-A fluorescent dye with two pyridyl groups as an electron-withdrawing-injecting anchoring group possessing a high coordinate bonding ability to Lewis acid sites on the TiO2 surface, which can lead to high dye loading on the TiO2 film and efficient electron injection, has been developed as a new type of D-π-A dye sensitizer for dye-sensitized solar cells.

Photovoltaic performance of dye-sensitized solar cells based on D–π–A type BODIPY dye with two pyridyl groups

D–π–A type boron dipyrromethene (BODIPY) dye YH-1, which has two pyridyl groups as electron-withdrawing-anchoring groups at the end of the 3- and 5-positions and a carbazole-diphenylamine moiety as an electron donor at the 8-position on the BODIPY core, was designed and developed as a photosensitizer for dye-sensitized solar cells (DSSCs). It was found that the dye YH-1 possesses a good light-harvesting efficiency (LHE) in the red/near-IR (NIR) region and good adsorption ability on TiO2 film. We demonstrate that the expansion of the π-conjugated system by the introduction of not only the carbazole-diphenylamine moiety and the thiophene unit at the 8-position but also two thienylpyridines at the 3- and 5-positions on the BODIPY core can lead to red-shift and broadening of the absorption band in the red/NIR region. DSSCs based on YH-1 exhibit incident photon-to-current conversion efficiency of ca. 10% over a range of 500 to 700 nm, with an onset at 800 nm.

Synthesis of diphenylamino-carbazole substituted BODIPY dyes and their photovoltaic performance in dye-sensitized solar cells

Non-alkylated BODIPY dye YHO-1 and hexa-alkylated BODIPY dye YHO-2, which have a diphenylamino-carbazole moiety as an electron-donating group at the 8-position on the BODIPY core and a carboxyhexyl group as an anchoring group on the carbazole ring, were designed and developed as photosensitizers for dye-sensitized solar cells (DSSCs). From the molecular structures of YHO-1 and YHO-2, when the two dyes were adsorbed on the TiO2 surface, it is assumed that the BODIPY core is located in close proximity to the TiO2 surface. The dye YHO-2 (Φf = 0.62) exhibits a significantly higher fluorescence quantum yield (Φf) than YHO-1 (Φf = 0.06). The short-circuit photocurrent density (Jsc) and solar energy-to-electricity conversion yield (η) for a DSSC based on YHO-2 are greater than those of YHO-1. This work demonstrates that fluorescent BODIPY dyes can inject electrons efficiently from the BODIPY core to the conduction band (CB) of the TiO2 electrode, but non-fluorescent BODIPY dyes result in lowering of photocurrent generation due to radiationless relaxation of the photoexcited dye.

Synthesis and electrical properties of novel oligothiophenes partially containing 3,4-ethylenedioxythiophenes

Five sorts of soluble oligothiophenes (trimer to undecamer) containing 3,4-ethylenedioxythiophene (EDOT) were synthesized, and their optical and electrochemical properties were investigated in relation to the chain length of oligothiophenes and the number of EDOT units. The introduction of the EDOT unit into a main oligothienylene unit induced a red shift of absorption bands and a negative shift of oxidation potentials. The conductivity of an electrochemically oxidized film of undecamer was found to be around 1 S cm−1. A thin-film field effect transistor was preliminary fabricated with neutral undecamer films and the hole mobility was determined.

In situ conductivity measurements of polythiophene partially containing 3,4-ethylenedioxythiophene and 3-hexylthiophene

Optical and electrochemical properties of a novel polythiophene partially containing 3,4-ethylenedioxythiophene (EDOT), poly(3,3″″-dihexyl-3′,4′,3‴,4‴-diethylenedioxy-2,2′:5′,2″:5″,2‴:5‴,2″″-quinquethiophene), in a neutral state, which was synthesized by polycondensation using direct C-H coupling reaction, were firstly investigated. In situ electrical conductivity of the doped polymer film was measured simultaneously with doping levels at different potentials to yield charge carrier mobilities as a function of doping level of the polymer. The highest conductivity was found to be around 101xa0Sxa0cm−1, which is almost one-order higher than that of an EDOT-containing polythiophene obtained by electrolytic polymerization, poly(3″,4″-ethylenedioxy-2,2′:5′,2″-terthiophene).

Thermoelectric performances of graphene/polyaniline composites prepared by one-step electrosynthesis

Composite films comprising graphene and polyaniline were prepared in one step by a facile electrochemical technique with graphene oxide (GO) and aniline monomer as raw materials, and their thermoelectric properties were investigated. Electrical conductivities of the composite films generated on the fluorine-doped tin oxide (FTO) electrode were dependent on the weight ratio of GO and aniline, and they exhibited a peak value of 30 S cm−1 at the GO/aniline ratio between 5u2006:u20061 and 10u2006:u20061, while Seebeck coefficients were less dependent on the weight ratio. The maximum power factor (PF) for the composite films was ca. 1 μW m−1 K−2. When the FTO electrode was replaced by the stainless steel electrode, conductivities of the composite films with the GO/aniline ratio of 8u2006:u20061 were increased up to ca. 130 S cm−1. As a result, the PF and the dimensionless thermoelectric figure-of-merit (ZT) at room temperature reached 3.6 μW m−1 K−2 and 0.008, respectively. The ZT value is the highest among those reported so far for graphene/PANI composites. Possible reasons for the conductivity enhancement on the stainless steel electrode are also discussed on the basis of electrochemical measurements and X-ray photoelectron spectroscopy.