Hironobu Ozawa

Significant improvement in the conversion efficiency of black-dye-based dye-sensitized solar cells by cosensitization with organic dye

The conversion efficiency of black-dye-based dye-sensitized solar cell (DSC) was improved by cosensitization with organic dye (NKX-2553 or D131). This improved conversion efficiency was further enhanced by employing deoxycholic acid (DCA) as a coadsobent. The highest conversion efficiency, 11.6% under AM 1.5 irradiation (100 mW cm−2), was obtained in DSC with black dye and D131 in the presence of DCA.

Dependence of the Efficiency Improvement of Black‐Dye‐Based Dye‐Sensitized Solar Cells on Alkyl Chain Length of Quaternary Ammonium Cations in Electrolyte Solutions

Dependence of the suppression of the backward electron transfer reaction from the TiO2 photoelectrode to I3(-) in the electrolyte on the alkyl chain length of the quaternary ammonium cation has been investigated for further efficiency improvement of high-performance cosensitized dye-sensitized solar cells (DSCs). The tetraheptylammonium cation was found to be more effective than the tetraethylammonium and tetrabutylammonium cations for the suppression of the backward electron transfer reaction without changing the conduction band energy of TiO2. 12.0% conversion efficiency, which is the second highest efficiency for DSCs based on ruthenium sensitizers, was achieved in the cosensitized DSC with Black dye and D131 by using an electrolyte solution containing a moderate concentration of tetraheptylammonium iodide.

Effects of Dye‐Adsorption Solvent on the Performances of the Dye‐Sensitized Solar Cells Based on Black Dye

The effects of the dye-adsorption solvent on the performances of the dye-sensitized solar cells (DSSCs) based on black dye have been investigated. The highest conversion efficiency (10.6 %) was obtained in the cases for which 1-PrOH and the mixed solvent of EtOH and tBuOH (3:1 v/v) were employed as dye-adsorption solvents. The optimized value for the dielectric constant of the dye-adsorption solvent was found to be around 20. The DSSCs that used MeOH as a dye-adsorption solvent showed inferior solar-cell performance relative to the DSSCs that used EtOH, 1-PrOH, 2-PrOH, and 1-BuOH. Photo- and electrochemical measurements of black dye both in solution and adsorbed onto the TiO(2) surface revealed that black dye aggregates at the TiO(2) surface during the adsorption process in the case for MeOH. Both the shorter electron lifetime in the TiO(2) photoelectrode and the greater resistance in the TiO(2)-dye-elecrolyte interface, attributed to the dye aggregation at the TiO(2) surface, cause the decrease in the solar-cell performance of the DSSC that used MeOH as a dye adsorption solvent.

Effective enhancement of the performance of black dye based dye-sensitized solar cells by metal oxide surface modification of the TiO2 photoelectrode

Effective enhancement of the performance of black dye based dye-sensitized solar cells has been achieved by MgO or Al(2)O(3) surface modification of the TiO(2) photoelectrode. The conversion efficiency was improved from 10.4% to 10.8% due to the blocking effect of the thin overlayer at the TiO(2) surface.

Highly efficient dye-sensitized solar cells based on a ruthenium sensitizer bearing a hexylthiophene modified terpyridine ligand

Two ruthenium sensitizers bearing a 4-substituted terpyridine derivative ligand (TUS-39 and TUS-41) have been synthesized for dye-sensitized solar cells (DSCs). Solar cell performances of DSCs with these TUS sensitizers, together with that of the DSC with TUS-38 which is a structurally analogous ruthenium sensitizer bearing an n-hexylthiophene modified terpyridine derivative ligand, have been evaluated to investigate a favorable substituent for improving the photosensitization ability of ruthenium sensitizers. Among the three TUS sensitizers, TUS-38 showed the highest conversion efficiency of 10.8% under AM 1.5 (100 mW cm−2) irradiation. The conversion efficiency of the DSC with TUS-38 can be increased to 11.1% by decreasing the dye-adsorption temperature from 20 °C to 4 °C, presumably due to the improvement in the molecular arrangement of the sensitizers adsorbed at the TiO2 surface. This improved conversion efficiency can be further enhanced to 11.9% by employing an electrolyte solution containing 1-ethyl-3-methylimidazolium iodide instead of conventional 1,2-dimethyl-3-n-propylimidazolium iodide. This conversion efficiency is considerably higher than that of Black dye (10.9%), which is one of the most famous and highly efficient ruthenium sensitizers, under the same conditions. Upon optimization of the dye-adsorption conditions and the electrolyte composition, an extremely high conversion efficiency of 11.9% can be obtained for the DSC with TUS-38.

Effects of cation composition in the electrolyte on the efficiency improvement of black dye-based dye-sensitized solar cells

The effects of the addition of the tetrabutylammonium cation in the electrolyte on the performance of a black dye-based dye-sensitized solar cell (DSC) have been investigated. The conversion efficiency of the cosensitized DSC with black dye and D131 was improved to 11.8% by using an electrolyte containing three kinds of cations.

Novel ruthenium sensitizers with a dianionic tridentate ligand for dye-sensitized solar cells: the relationship between the solar cell performances and the electron-withdrawing ability of substituents on the ligand

Five novel ruthenium sensitizers (TUS sensitizers) with a dianionic tridentate ligand (pyridine-2,6-dicarboxyamidato and its derivatives) have been synthesized for application to dye-sensitized solar cells (DSCs). These TUS sensitizers have much larger molar absorption coefficients in the wavelength range below 600 nm compared with those of Black dye which is a structural analog and a highly efficient ruthenium sensitizer. The energy levels of HOMOs and LUMOs of TUS sensitizers shifted to the positive direction with increasing the electron-withdrawing ability of the substituents on the dianionic tridentate ligand. The energy levels of HOMO and LUMO showed linear correlation with respect to the Hammett constant of the substituents. The DSCs with TUS sensitizers showed much lower performances than that of Black dye. Both inferior adsorptivity on the TiO2 surface and unfavorable energy levels of HOMOs and LUMOs for the effective electron transfer reactions in the DSCs are considered to be the main reasons for the much lower performances of TUS sensitizers. The conversion efficiency of the DSC with a TUS sensitizer increased with increasing the electron-withdrawing ability of the substituents on the dianionic tridentate ligand. The observed linear relationship between the conversion efficiency and the driving force of the reduction process of the oxidized form of dyes by I(-) suggests that the dye regeneration process is a rate-determining step in the DSCs with TUS sensitizers.

Efficient ruthenium sensitizer with an extended π-conjugated terpyridine ligand for dye-sensitized solar cells.

A ruthenium sensitizer with an extended π-conjugated terpyridine (TUS-42) has been synthesized for dye-sensitized solar cells (DSCs). Upon extension of the π-conjugated system of the terpyridine ligand, the conversion efficiency of the DSC with TUS-42 improved successfully to 10.7%, which is almost comparable to that of one of the most efficient ruthenium sensitizers (Black dye). Interestingly, an extremely large short-circuit current density (Jsc) value (22.7 mA/cm(2)) was obtained in the DSC with TUS-42 even though the amount of dye adsorption to the TiO2 photoelectrode is relatively small.