Yoshihiro Yamaguchi

Transparent conductive oxide layer-less dye-sensitized solar cells consisting of floating electrode with gradient TiOx blocking layer

A transparent conductive oxide less dye-sensitized solar cell (TCO-less DSC) consisting of a glass/a floating electrode (FE)/a stained nanoporous titania layer/a gel electrolyte sheet/a Pt layer/a Ti sheet is reported. The FE is composed of a stainless mesh sheet covered with a gradient TiOx layer, which suppressed back-electron transfers from the stainless to electrolytes. The efficiency increased from 2.87% to 4.68% by replacing a conventional dense TiO2 blocking layer with the gradient TiOx layer. The cell in this architecture gave the efficiency of 5.56% after optimization.

Ru Dye Uptake under Pressurized CO2 Improvement of Photovoltaic Performances for Dye-Sensitized Solar Cells

Swift uptake of Ru dyes and improvement of photovoltaic performances for dye-sensitized solar cells (DSC) are reported. Ru dyes such as black dye [(C 4 H 9 ) 4 N] 3 [Ru(Htcterpy)(NCS)3] (tcterpy = 4,4,4-tricarboxy-2,2:6,2-terpyridine) and N3 dye [cis-di(thiocyanato)-N,N-bis(2,2-bipyridyl-4,4-dicarboxylato) ruthenium (II)] are adsorbed on nano-porous TiO 2 layers under a pressurized CO 2 atmosphere to bond Ru dyes on inner surfaces of TiO 2 in nano-porous layers effectively. The time needed for N3 dye adsorption under a pressurized CO 2 condition is drastically shortened to 30 min from 300 min needed for a dipping process. The amount of N3 dye molecules increases from 15 to 20 nmol/cm 2 /μm when N3 dye is adsorbed under a pressurized CO 2 atmosphere. The pressurized CO 2 process increases short circuit current, fill factor, and open circuit voltage which are associated with better coverage of TiO 2 surfaces with dye molecules. They decrease surface traps of porous TiO 2 layers. This retards back electron transfers from TiO 2 layers to iodine in electrolytes and facilitates electron diffusion in TiO 2 layer. Measurement of the electron lifetime and electron diffusion coefficient in the cells supports the mechanism.

Tandem Dye-Sensitized Solar Cells Fabricated on Glass Rod without Transparent Conductive Layers

A tandem dye-sensitized solar cell was fabricated on a glass rod without a transparent conductive oxide layer (TCO-less GR-DSSC). Two model dyes having λmax = 429 nm (Dye II) and λmax = 646 nm (Dye I) respectively were used to examine the potential of the cell. The incident photon to current conversion efficiency (IPCE) curve of the TCO-less GR-DSSC had two peaks at around 490 and 600–650 nm. Open circuit voltage (Voc) of the TCO-less GR-DSSC was 1.13 V which was the sum of the Voc (0.57 V) of each single cell. The results strongly demonstrate that the cell has a tandem character.

Probing TiO2/Dye Interface in Dye Sensitized Solar Cells Using Surface Potential Measurement

Surface potential measurement using scanning Kelvin-probe microscopy was conducted to investigate the relationship between dye characteristics and open circuit voltage (Voc). It was observed that Voc increased with the increase in surface potential of dye as compared to that of bare TiO2 giving increased efficiency of dye sensitized solar cells. Addition of chenodeoxycholic acid (DCA) as co-adsorbent caused positive shift of surface potential, which explained the increase of Voc upon DCA incorporation. It was further explained by the negative shift of TiO2 conduction band edge in the presence of DCA.

Transparent Conductive Oxide Layer-Less Three Dimensional Dye Sensitized Solar Cells: Fabrication of Ionic Path in Three Dimensional Ti Electrode

A transparent conductive oxide-less dye-sensitized solar cell (TCO-less DSC) consisting of a thick and porous Ti electrode is reported. The Ti electrode was contacted with the back of a stained porous titania layer. A thick Ti electrode prepared by conventional sputtering prevented ionic diffusions through the Ti electrode and decreased photovoltaic performance. Tetrapod-shaped ZnO crystals were used to prepare straight and continuous nanopores in the Ti electrode to maintain the ionic diffusion. 8% efficiency of the TCO-less DSC is also reported.

Dye-Sensitized Solar Cells Consisting of 3D-Electrodes—A Review: Aiming at High Efficiency From the View Point of Light Harvesting and Charge Collection

Directions to high efficiency dye-sensitized solar cells (DSCs) are reviewed in terms of light harvesting and charge collection. Three dimensional DSCs characterized by a double dye layer electrode, a floating electrode, and a fiber type electrode are proposed. The potentiality of each structure was discussed by using each model cell. Transparent conductive layerless electrodes were the key structures in these cells. Fabrication processes and fundamental performances are reported. Finally, it is concluded that dyes having high photoconversion effaciency in the near IR and IR regions are essential for realizing these tandem and hybrid cells.

SYNTHESIS OF CHROMANS BY PHOTOSENSITIZED ELECTROCHEMICAL OXIDATION OF SULFIDES MEDIATED BY METHYLENE BLUE

Abstract o-Quinone methides were generated by a photosensitized cleavage of sulfides under neutral conditions using visible light provided by a 100 Watt spot light and methylene blue as a sensitizer. The key step in the oxidative cleavage is the transfer of one electron form the sulfide to the electronically excited visible dye. The resulting phenylthio radical cation undergoes frangmentation, and the correspondign o-quinone methides are generated and trapped by varied alkenes to yield chromans.

Fine tuning the structure of unsymmetrical squaraine dyes towards the development of efficient dye-sensitized solar cells

Creation of molecular asymmetry in the organic sensitizing dyes has been demonstrated for enhancing the photoconversion efficiency due to unidirectional flow of electron after the photoexcitation. Molecular structures for direct indole ring carboxy-functionalized unsymmetrical squaraine dyes have been optimized by fine tuning the molecular structures and judicious selection of the substituents to prevent the dye aggregation and electron recombination. Best efficiency of 4.42 % was achieved for unsymmetrical squaraine dye SQ-64 with a short circuit current density of 11.22 mA/cm2, a fill factor of 0.61 and an open circuit voltage of 0.64 V under standard AM 1.5 simulated solar irradiation.

Local reflection micro-spectroscopy of excitons in fibril-shaped molecular J-aggregates prepared in PVA thin films

Abstract Results on microscopic reflection imaging and spectroscopy of fibril-shaped J-aggregates of pseudoisocyanyne dyes prepared in thin film matrices of polyvinyle alcohol (PVA) are reported. We have found that formation of fibril-shaped structures with sub-micron widths is also possible in PVA. Despite the aggregation mechanism should be different from those in polyvinyl sulfate, reflection images and local spectroscopy show that the exciton–polariton characters are basically similar in the two matrices. Anomalous polarization dependence is also observed in PVA and seems rather strengthened.

Dye-sensitized solar cells based on axially ligated phosphorus-phthalocyanine dyes

Dye-sensitized solar cells with axially anchored phosphorous-phthalocyanine dyes were fabricated for the first time. Although the phosphorus-phthalocyanine dyes do not have a conventional anchoring group (–COOH), these dyes could be absorbed on a TiO2 semiconductor surface. After the optimization of energy levels, a 24% incident photon-to-current efficiency (IPCE) was observed at 710 nm with an IPCE curve edge of 800 nm. The efficiency was 2.67%, which was higher than those of previously reported dye-sensitized solar cells with axially anchored phthalocyanine dyes (less than 1%).