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25 results on '"Wolfer, Pascal"'

4. Stable holographic gratings with small-molecular trisazobenzene derivatives

Author

Kreger, Klaus, Wolfer, Pascal, Audorff, Hubert, Kador, Lothar, Stingelin-Stutzmann, Natalie, Smith, Paul, and Schmidt, Hans-Werner

Subjects
Azo compounds -- Structure, Azo compounds -- Chemical properties, Benzene -- Chemical properties, Diffraction gratings -- Analysis, Holography -- Analysis, Phase transformations (Statistical physics) -- Analysis, Refractive index -- Measurement, Chemistry
Abstract

The chemical structures designed by inserting decoupling spacers between a trisfunctionalized benzene core and the three azobenzene moieties, as well as adding polar end groups to the latter that allow formation of both an amorphous and a liquid-crystalline phase. The obtained nonpolymeric, azobenzene-containing compounds could find valuable application for fabrication of stable holographic volume gratings.

Published
2010

6. Photo-induced molecular alignment of trisazobenzene derivatives

Author

Wolfer, Pascal, Audorff, Hubert, Kreger, Klaus, Kador, Lothar, Schmidt, Hans-Werner, Stingelin, Natalie, and Smith, Paul

Abstract

Optically active small-molecular trisazobenzene derivatives are explored that allow facile photo-induced fabrication of holographic volume gratings which are unusually stable over time compared to structures based on other small-molecular organic compounds. The origin of this favorable characteristic of such architectures is investigated with three compounds that structurally differ only in the length of an alkyl spacer positioned between the molecular core and the active azobenzene chromophores. Species comprising spacers of sufficient length, and that exhibit a latent liquid-crystalline phase, feature efficient formation of stable, ordered domains in which the three side groups orient perpendicular to the polarization of the inscribing light beam. It is demonstrated that molecular order in these domains can be significantly improved by annealing at temperatures between the glass transition temperature and the clearing point of the specific compounds. This phenomenon allows combining the highly desirable processing characteristic of relatively short holographic writing times with small molecules in the fabrication of stable volume gratings, the latter feature so far having been reserved predominantly for polymeric species.

Published
2011
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7. Ordering molecular organics into functionality

Author

Wolfer, Pascal, Broer, Dirk J., and Smith, Paul

Subjects
Electric engineering, MATRIXVERBUNDWERKSTOFFE, AZOBENZENE (MONOCYCLIC AROMATIC HYDROCARBONS), ddc:621.3, MATRIX COMPOSITES, HALBLEITERMATERIALIEN (ELEKTROTECHNIK), ERZEUGUNG DÜNNER SCHICHTEN (PHYSIK VON MOLEKULARSYSTEMEN), MOLEKULARELEKTRONIK, MIKROSTRUKTUR VON MOLEKULARSYSTEMEN (PHYSIK), MICROSTRUCTURE OF MOLECULAR SYSTEMS (PHYSICS), SEMICONDUCTOR MATERIALS (ELECTRICAL ENGINEERING), ORGANISCHE VERBINDUNGEN UND ORGANISCHE MOLEKÜLE, OPTOELECTRONIC MATERIALS (OPTOELECTRONICS), MOLECULAR ELECTRONICS, OPTOELEKTRONISCHE MATERIALIEN (OPTOELEKTRONIK), ORGANIC COMPOUNDS AND ORGANIC MOLECULES, Engineering & allied operations, AZOBENZOL (MONOCYCLISCHE AROMATISCHE KOHLENWASSERSTOFFE), PRODUCTION OF THIN FILMS (PHYSICS OF MOLECULAR SYSTEMS), ddc:620
Published
2011

17. A flexible n-type organic semiconductor for optoelectronics

Author

Gui, Ke, primary, Mutkins, Karyn, additional, Schwenn, Paul E., additional, Krueger, Karsten B., additional, Pivrikas, Almantas, additional, Wolfer, Pascal, additional, Stingelin Stutzmann, Natalie, additional, Burn, Paul L., additional, and Meredith, Paul, additional

Published
2012
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22. Efficient, Large Area, and Thick Junction Polymer Solar Cells with Balanced Mobilities and Low Defect Densities.

Author

Armin, Ardalan, Hambsch, Mike, Wolfer, Pascal, Jin, Hui, Li, Jun, Shi, Zugui, Burn, Paul L., and Meredith, Paul

Subjects
ELECTRIC power conversion, SOLAR cells, ELECTRODES, SEMICONDUCTOR junctions, INTERMOLECULAR interactions
Abstract

The high power conversion efficiencies (PCEs) of laboratory-scale polymer-based organic solar cells are yet to translate to large area modules because of a number of factors including the relatively large sheet resistance of available transparent conducting electrodes (TCEs), and the high defect densities associated with thin organic semiconductor junctions. The TCE problem limits device architectures to narrow connected strips (<1 cm) causing serious fabrication difficulties and extra costs. Thin junctions are required because of poor charge transport (imbalanced mobilities) in the constituent organic semiconductors. These issues are addressed using a combination of approaches to create thick junctions conformally coated on low sheet resistance metal grid TCEs. An essential feature of these thick junctions is balanced carrier mobilities, which affords high fill factors and efficient carrier extraction. Conformal coating is achieved by promoting enhanced intermolecular interactions in the coating solution using a high molecular weight polymeric semiconductor and appropriate solvent system. This combination of balanced mobilities, conformal coating and metallic grid TCEs is a simple and generic approach to the fabrication of defect-free large area organic solar cells (OSCs). The approach is demonstrated with 25 cm2 monolithic devices possessing aperture-corrected power conversion efficiencies of 5% and fill factors exceeding 0.5. [ABSTRACT FROM AUTHOR]

Published
2015
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24. LightStability of Polydialkylstannanes

Author

Choffat, Fabien, Wolfer, Pascal, Smith, Paul, and Caseri, Walter

Abstract

This study deals with the stability of polydialkylstannanes in solution and in the bulk, in particular under exposure to light, which was found to cause degradation more severely than water or oxygen. Decomposition of the polydialkylstannanes under argon atmosphere in solution proceeded by an unzipping mechanism, most likely initiated by scission of a SnSn bond. While solvents and additives influenced polystannane degradation, the length of the alkyl groups was not particularly relevant, indicating that steric effects played a minor role in this process. In unreactive solvents, the polystannanes were the least stable and cyclic oligostannanes formed as decomposition products. Polystannanes in solution were found to be most stable in dichloromethane or styrene, which gave rise to the formation of Bu2ClCH2SnCl or polystyrene, indicating that the polystannanes acted in the latter case as a photoinitiator. Addition of radical scavengers and selected dyes improved the stability of polystannanes toward light. Exposure of bulk polydialkylstannanes to ambient caused the formation of oligoalkyltinoxides.

Published
2010
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25. Blended polymer semiconductors

Author

Sirringhaus, H., Goffri, S., Janssen, R.A.J., Radano, C.P., Smith, P., Muller, C., Wolfer, Pascal, Stutzmann, N., Macromolecular and Organic Chemistry, Molecular Materials and Nanosystems, and Polymer Technology

Abstract

A method for forming a semiconductor body comprises: forming a mixt. of an org. semiconducting material (e.g., poly-3-hexylthiophene) and a binder (e.g., polyethylene) material; causing the semiconducting material to at least partially solidify; and causing the binder material to crystallize in such a way as to cause the semi conducting material to at least partially segregate from the binder material. [on SciFinder (R)]

Published
2008

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