Heiner J. Gores

Overcoming kinetic limitations of electron injection in the dye solar cell via coadsorption and FRET.

A new, extremely simple concept for the use of energy transfer as a means to the enhancement of light absorption and current generation in the dye solar cell (DSC) is presented. This model study is based upon a carboxy-functionalized 4-aminonaphthalimide dye (carboxy-fluorol) as donor, and (NBu4)2[Ru(dcbpy)2(NCS)2] (N719) as acceptor chromophores. A set of three different devices is assembled containing either exclusively carboxy-fluorol or N719, or a mixture of both. This set of transparent devices is characterized via IV-measurements under AM1.5G and monochromatic illumination and their light-harvesting and external quantum efficiencies (LHE and EQE, respectively) are determined as well. It is shown that the device containing only the donor chromophore has a marginal power conversion efficiency, thus indicating that carboxy-fluorol is a poor sensitizer for the DSC. Cyclovoltametric measurements show that the poor sensitization ability arises from the kinetic inhibition of electron injection into the TiO2 conduction band. Comparing the spectral properties of the DSCs assembled presently, however, demonstrates that light absorbed by carboxy-fluorol is almost quantitatively contributing to the photocurrent if N719 is present as an additional sensitizer. In this case, N719 acts as a catalyst for the sensitization of TiO2 by carboxy-fluorol in addition to being a photosensitizer. Evaluation of the maximum output power under blue illumination shows that the introduction of an energy-donor moiety via coadsorption, leads to a significant increase in the monochromatic maximum output power. This result demonstrates that energy transfer between coadsorbed chromophores could be useful for the generation of current in dye-sensitized solar cells.

Lithium Bis[5‐fluoro‐2‐olato‐1‐benzenesulfonato (2‐)‐O,O′]borate(1‐), a New Anodically and Cathodically Stable Salt for Electrolytes of Lithium‐Ion Cells

Synthesis, characterization, and electrochemical investigations of lithium bis[5-fluoro-2-olato-1-benzenesulfonato(2-)-O,O{prime}]borate(1-), a new salt for lithium-ion cells in ethylene carbonate (EC)-dimethylcarbonate (DMC) mixtures are presented. At platinum electrodes the anodic oxidation limit is about 4.6 V, in good agreement with an estimation based on semiempirical quantum-mechanical calculations. At Al electrodes its behavior is similar to that obtained for LiPF{sub 6}/EC/DMC (1:1).

Temperature Dependent Impedance Analysis of Binary Ionic Liquid Electrolytes for Dye-Sensitized Solar Cells

At platinum electrodes kinetics of the I - /I - 3 electrode reaction were studied at two potential electrolyte systems for dye-sensitized solar cells (DSSCs) based on binary ionic liquid (IL) blends, i.e., 1-ethyl-3-methylimidazolium dicyanamide ([EMIM] [N(CN) 2 ])/1-methyl-3-propylimidazolium iodide ([PMIM]I) and l-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM] [BF 4 ])/[PMIM]I, respectively. The charge transfer resistances of the electrode reaction were determined via impedance spectroscopy for electrolyte blends at a mixing ratio of ILs of 9 mol % [PMIM]I (for [EMIM][N(CN)2]/[PMIM]I) and 10 mol % [PMIM]I (for [EMIM][BF 4 ]/[PMIM]I) up to 100 mol % [PMIM]I. In addition, the influence of iodine concentration on the electrode reaction was investigated for both electrolyte systems. The measurements were taken in a temperature range of 25 to 60°C to analyze the electrolyte properties in view of thermal stress of the DSSC for later practical application. Furthermore, exchange current densities were determined: the expected Arrhenius behavior was observed. Activation energies were obtained by fitting linearized Arrhenius plots.

Chloride‐Free Method to Synthesise New Ionic Liquids with Mixed Borate Anions

Chloride avoided! A new chloride-free method to synthesise ionic liquids (ILs) with mixed borate anions, starting from tetrafluoroborate compounds, has been developed and a number of examples including some new ILs are presented (see scheme; [CAT](+) = cation). It is widely applicable and allows access to mixed borates with various types of ligands in a straightforward manner.

Trialkylsulfonium dicyanamides - a new family of ionic liquids with very low viscosities

Trialkylsulfonium dicyanamides show surprisingly low viscosities down to -20 degrees C and are therefore highly interesting liquid materials for separation processes and electrolyte applications at low temperatures.

Fast Multichannel Precision Thermometer

This paper describes a fast multichannel precision thermometer working in a temperature range from -50degC to +40degC. Thermistors are used as temperature sensing elements. A detailed discussion of the choice of thermistor and design of the circuitry is given. It is shown that accuracy similar to that of calibrated platinum thermometers can be achieved by calibration of thermistors. During our tests, the accuracy of the thermometer was both mathematically and experimentally analyzed in detail. The stability of 30 thermistors after six months of laboratory use was analyzed. Deviations smaller than 30 mK in the range from -50degC to+10degC were observed.

Salt-in-Polymer Electrolytes Based on Polysiloxanes for Lithium-Ion Cells: Ionic Transport and Electrochemical Stability

In this work, the ion transport and the electrochemical stability has been investigated for cross linked salt-in-polysiloxane membranes containing the two lithium salts with boron based anions, i.e. LiDFOB (lithium difluoro(oxalato)borate) and LiBOB (lithium bis(oxalato)borate) have been investigated. The stability was characterized by cyclic voltammetry at 70 °C in a three electrode cell with Li as counter and reference electrodes and a nickel or platinum working electrode. The electrochemical stability window of polysiloxane based electrolytes ranged between 0 V and 4.7 V vs. Li/Li + . The high ionic conductivity of 6.61 x 10 -2 mS/cm at 30 °C has been examined with impedance spectroscopy on blocking electrodes. The investigated polymer electrolytes showed an outstanding thermal resistance as confirmed by thermal analysis with DSC. Furthermore, analysis of the lithium transference number has been carried out using the potentiostatic polarization method introduced by BRUCE and VINCENT.

A novel method for in situ measurement of solubility via impedance scanning quartz crystal microbalance studies

We introduce here a novel in situ measurement method for solubility of solids in various liquids. Without any calibration the saturation point can be obtained in a relative manner. We exemplified the new method at four systems including water, organic carbonates and an ionic liquid as the solvents and various salts as dissolved solids.