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Tsukuba, Japan

Matsui M.,Gifu University | Asamura Y.,Gifu University | Kubota Y.,Gifu University | Funabiki K.,Gifu University | And 3 more authors.

Substituited triple rhodanine indoline dyes showed higher performance than known triple rhodanine derivative (D150). A few triple rhodanine indoline derivatives showed comparable conversion efficiency to D149. © 2010 Elsevier Ltd. All rights reserved. Source

Tefashe U.M.,Carl von Ossietzky University | Rudolph M.,Justus Liebig University | Miura H.,Chemicrea Co. | Schlettwein D.,Justus Liebig University | Wittstock G.,Carl von Ossietzky University
Physical Chemistry Chemical Physics

Porous ZnO electrodes on fluorine-doped tin oxide (FTO) were prepared by electrochemical deposition from an O 2-saturated ZnCl 2 solution in the presence of eosin Y as a structure directing agent (SDA). Sensitization was reached by desorption of the SDA and subsequent adsorption of the indoline dye D149. The influence of film thickness and dye concentration in the films on their photovoltaic characteristics, recombination, and dye regeneration kinetics was investigated. The recombination kinetics was analyzed by time-resolved photovoltage measurements. The dye regeneration by iodide ions in the electrolyte was investigated using scanning electrochemical microscopy (SECM) feedback mode approach curves. Analysis of a SECM kinetic model shows strongly different effective D149 regeneration rate constants for D149-ZnO electrodes of systematically varied film thickness and dye loading. It was found that the short-circuit current density J sc and correlated directly with the adsorbed dye concentration. was found to be independent of the dye loading but correlated strongly with the dye concentration in the film or inversely with the film thickness. Furthermore, we discussed the perspective of correlating macroscopic cell characteristics with SECM kinetics data. © 2012 the Owner Societies. Source

Tefashe U.M.,Carl von Ossietzky University | Loewenstein T.,Justus Liebig University | Miura H.,Chemicrea Co. | Schlettwein D.,Justus Liebig University | Wittstock G.,Carl von Ossietzky University
Journal of Electroanalytical Chemistry

A scanning electrochemical microscope (SECM) in the feedback and generation-collection modes was used to investigate the regeneration of photoexcited dye cations at the semiconductor/electrolyte interface in a dye-sensitized solar cell (DSSC) based on ZnO/D149. An effective dye regeneration rate constant kox of 9.55 × 107 cm 9/2 mol-3/2 s-1 was obtained from feedback mode experiments at different wavelengths and light intensities on ZnO/D149 electrodes. Illuminated regions of the dye-sensitized electrodes could be differentiated from non-illuminated regions by local imaging in SECM generation-collection experiments with I- as redox mediator. We also report SECM feedback measurements on non-illuminated dye-sensitized electrodes to investigate the electron transfer kinetics of dissolved redox couples at the underlying FTO substrate. © 2010 Published by Elsevier B.V. Source

Docampo P.,University of Oxford | Tiwana P.,University of Oxford | Sakai N.,Toin University of Yokohama | Miura H.,Chemicrea Co. | And 3 more authors.
Journal of Physical Chemistry C

The coating of n-type mesoporous metal oxides with nanometer thick dielectric shells is a route that has proven to be successful at enhancing the efficiency of some families of dye-sensitized solar cells. The primary intention is to introduce a "surface passivation layer" to inhibit recombination between photoinduced electrons and holes across the dye-sensitized interface. However, the precise function of these dielectric interlayers is often ambiguous. Here, the role of a thin MgO interlayer conformally deposited over mesoporous SnO 2 in liquid electrolyte and solid-state dye-sensitized solar cells is investigated. For both families of devices the open-circuit voltage is increased by over 200 mV; however, the short-circuit photocurrent is increased for the solid-state cells, but reduced for the electrolyte based devices. Through electronic and spectroscopic characterization we deduce that there are four distinct influences of the MgO interlayer: It increases dye-loading, slows down recombination, slows down photoinduced electron transfer, and results in a greater than 200 mV shift in the conduction band edge, with respect to the electrolyte redox potential. The compilation of these four factors have differing effects and magnitudes in the solid-state and electrolyte DSCs but quantitatively account for the difference in device performances observed for both systems with and without the MgO shells. To the best of our knowledge, this is the most comprehensive account of the role of dielectric shells in dye-sensitized solar cells and will enable much better interfacial design of photoelectrodes for DSCs. © 2012 American Chemical Society. Source

Rudolph M.,Justus Liebig University | Yoshida T.,Yamagata University | Miura H.,Chemicrea Co. | Schlettwein D.,Justus Liebig University
Journal of Physical Chemistry C

A pathway to improve the light-harvesting efficiency of dye-sensitized solar cells based on porous electrodeposited ZnO films is presented. Cosensitization with the indoline dyes D149 and D131 and the squaraine dye SQ2 leads to panchromatic light harvesting and photovoltaic activity. When coadsorbates are employed to prevent dye aggregation on the ZnO surface, an increase in the short-circuit photocurrent and overall efficiency compared to reference cells with D149, or D149 and D131 is attained. The overall performance of cosensitized cells containing SQ2, however, is limited by low open-circuit voltages and fill factors. By use of electrochemical impedance spectroscopy, current-voltage characterization in the dark and under illumination, and charge extraction measurements, recombination reactions and the distribution of trap states in the ZnO films are investigated, and the origins of the limited open-circuit voltages and fill factors in cells with SQ2 are revealed. © 2014 American Chemical Society. Source

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