Effect of Side Groups for Ruthenium Bipyridyl Dye on the Interactions with Iodine in Dye-Sensitized Solar Cells

A density functional theory (DFT) study was performed to elucidate the effect of the side group (X) in Ru(H₂dcbpy)(X₂bpy)(NCS)₂ dye on the interactions with iodide ions (I^– and I₃^–) and iodine molecule (I₂), where X is a carboxyl, nonyl, amino, or 1-pyrrolyl group, and dcbpy and X₂bpy represent 4,4′-dicarboxy-2,2′-bipyridine and 4,4′-X₂-2,2′-bipyridine, respectively. Oxidized dyes interact with I^– via the S atom of the NCS ligand perpendicular to the H₂dcbpy ligand. The relative interaction strength between the dye and I^– is amino < nonyl <1-pyrrolyl < carboxyl group. Except for dye possessing amino groups, a second I^– bonds to the first I^–, and the iodides weakly interact with the C–H bond of X₂dcbpy ligand. Additionally, I₂ interacts via the S atom of the NCS ligand perpendicular to H₂dcbpy of the neutral dye, and this interaction becomes stronger in the order of carboxyl < 1-pyrrolyl < nonyl < amino group dye. Only the neutral dye possessing amino groups interacts with I₃^– via N–H···I bonds. On the basis of theoretical results, the effect of side groups for Ru bipyridyl dye on both regeneration of oxidized dye with I^– species and recombination related to the interactions with I₂ and I₃^– species in the dye-sensitized solar cells is discussed

Theoretical Study on the Intermolecular Interactions of Black Dye Dimers and Black Dye–Deoxycholic Acid Complexes in Dye-Sensitized Solar Cells

Herein the intermolecular interactions in Ru­(H₃tcterpy)­(NCS)₃ (black dye) dimers, where tcterpy is 4,4′,4″-tricarboxy-2,2′:6′,2″-terpyridine, deoxycholic acid (3α,12α-dihydroxy-5β-cholan-24-oic acid, DCA) dimers, and black dye–DCA complexes in acetonitrile were investigated using density functional theory (DFT) and time-dependent DFT (TD-DFT). Among the five resulting black dye dimers, the most preferable species (<b>BB1</b>) forms intermolecular hydrogen bonds via the carboxyl groups and has a centrosymmetric structure similar to that reported for a black dye crystal. Theoretical calculations indicate six black dye–DCA complexes, and the most stable configuration (<b>BC1</b>) has three intermolecular hydrogen bonds between the two carboxyl groups of the dye ligand and one carboxyl and two hydroxyl groups of DCA. <b>BC1</b> has a higher intermolecular interaction energy than <b>BB1</b>. On the basis of these theoretical results, the structure of black dye aggregation and the aggregation suppression mechanism by DCA during the immersion process to prepare for dye-sensitized solar cell (DSSC) are discussed

Discovery of Overcoating Metal Oxides on Photoelectrode for Water Splitting by Automated Screening

We applied an automated semiconductor synthesis and screen system to discover overcoating film materials and optimize coating conditions on the BiVO₄/WO₃ composite photoelectrode to enhance stability and photocurrent. Thirteen metallic elements for overcoating oxides were examined with various coating amounts. The stability of the BiVO₄/WO₃ photoelectrode in a highly concentrated carbonate electrolyte aqueous solution was significantly improved by overcoating with Ta₂O₅ film, which was amorphous and porous when calcined at 550 °C. The photocurrent for the water oxidation reaction was only minimally inhibited by the presence of the Ta₂O₅ film on the BiVO₄/WO₃ photoelectrode

Cs-Modified WO₃ Photocatalyst Showing Efficient Solar Energy Conversion for O₂ Production and Fe (III) Ion Reduction under Visible Light

Cs-modification effects of WO₃ on photocatalytic O₂ evolution and Fe (III) ion reduction over WO₃ under visible light irradiation were investigated. WO₃ having cation-exchange ability at the surface was successfully prepared by hydrothermal and impregnation methods using cesium aqueous solutions. The photocatalytic activity of Cs-modified WO₃ was partially improved by the ion-exchange of Cs⁺ for H⁺ and Fe²⁺, and more than 10 times higher than that of WO₃ without any treatment. The optimized WO₃ showed 48 times higher quantum efficiency (19% at 420 nm) than that reported previously under visible light, and showed a high solar-to-chemical energy conversion efficiency (η_sun = 0.3%). This η_sun value is comparable to the solar-to-product energy conversion efficiencies of natural plant photosynthesis for biomass energy