Highlights 2014

POM and GIWAXS of benzodithiophene terthiophene rhodanine
Kuan Sun, Zeyun Xiao, Shirong Lu, Wojciech Zajaczkowski, Wojciech Pisula, Eric Hanssen, Jonathan M. White, Rachel M. Williamson, Jegadesan Subbiah, Jianyong Ouyang, Andrew B. Holmes, Wallace W.H. Wong, David J. Jones
A molecular nematic liquid crystalline material for high-performance organic photovoltaics
Solution-processed organic photovoltaic cells (OPVs) hold great promise to enable roll-to-roll printing of environmentally friendly, mechanically flexible and cost-effective photovoltaic devices. Nevertheless, many high-performing systems show best power conversion efficiencies (PCEs) with a thin active layer (thickness is ~100 nm) that is difficult to translate to roll-to-roll processing with high reproducibility. Here we report a new molecular donor, benzodithiophene terthiophene rhodanine (BTR), which exhibits good processability, nematic liquid crystalline behavior and excellent optoelectronic properties. A maximum PCE of 9.3% is achieved under AM 1.5G solar irradiation, with fill factor reaching 77%, rarely achieved in solution-processed OPVs. Particularly promising is the fact that BTR-based devices with active layer thicknesses up to 400 nm can still afford high fill factor of ~70% and high PCE of ~8%. Together, the results suggest, with better device architectures for longer device lifetime, BTR is an ideal candidate for mass production of OPVs.
© Nature (2014)
POM and GIWAXS of benzodithiophene terthiophene rhodanine
Controlled Folding of Graphene: GraFold Printing
T. Hallam, A. Shakouri, E. Poliani, A. P. Rooney, I. Ivanov, A. Potie, H. K. Taylo, M. Bonn, D. Turchinovich, S. J. Haigh, J. Maultzsch, and G. S. Duesberg
Controlled Folding of Graphene: GraFold Printing
In a collaborative work together with Trinity College Dublin, Nanhyang Technological University, Technical University of Berlin, University of Manchester, and University of California, Berkeley, the MPIP researchers Ivan Ivanov, Mischa Bonn, and Dmitry Turchinovich have demonstrated that a strong photoconductivity anisotropy can be efficiently created in graphene by controlled mechanical folding of graphene, also called GraFold printing method. It was found, that although the well-defined nano-folds contain only about 5% of material, the photoconductivity anisotropy in a folded graphene sample reaches as much as 40%. This fold-induced anisotropy is particularly important for potential applications of graphene in electronics and optoelectronics.
© ACS (2014)
Controlled Folding of Graphene: GraFold Printing
Functionalization topologies of fourfold cyano-substituted terrylenediimides as n-type organic semiconductors.
Glauco Battagliarin, Sreenivasa Reddy Puniredd, Sebastian Stappert, Wojciech Zajaczkowski, Suhao Wang, Chen Li, Wojciech Pisula, Klaus Müllen
Ortho- vs Bay-Functionalization: a Comparative Study on Tetracyano-Terrylenediimides
A detailed study about the impact of the functionalization topologies of fourfold cyano-substituted teyrrylenediimides on the optoelectronic properties, self-organization from solution, solid-state packing, and charge carrier transport in field-effect transistors is presented. The ortho-substitution preserves the planarity of the core and favors high order in solution processed films. However, the strong intermolecular interactions lead to a microstructure with large aggregates and pronounced grain boundaries which lower the charge carrier transport in transistors. In contrast, the well-soluble bay-functionalized terrylenediimide forms only disordered films which surprisingly result in enhanced n-type transport in transistors.
© Wiley (2014)
Functionalization topologies of fourfold cyano-substituted terrylenediimides as n-type organic semiconductors.
Sterically demanding chromophores conjugated with oligoprolines of increasing length and rigidity form supramolecular structures with increasing order, whereas the individual building blocks do not self-assemble.
Dr. Urszula Lewandowska, Wojciech Zajaczkowski, Dr. Long Chen, Dr. Francelin Bouillière, Dr. Dapeng Wang, Dr. Kaloian Koynov, Dr. Wojciech Pisula, Prof. Klaus Müllen and Prof. Helma Wennemers
Hierarchical Supramolecular Assembly of Sterically Demanding p-Systems by Conjugation with Oligoprolines
Self-assembly from flexible worm-like threads via bundles of rigid fibers to nanosheets and nanotubes was achieved by covalent conjugation of perylene monoimide chromophores with oligoprolines of increasing length. Whereas the chromophoric p-system and the peptidic building block do not self-aggregate, the covalent conjugates furnish well-ordered supramolecular structures with a common wall/fiber thickness. Their morphology is controlled by the number of repeat units and can be tuned by seemingly subtle structural modifications.
© Wiley (2014)
Sterically demanding chromophores conjugated with oligoprolines of increasing length and rigidity form supramolecular structures with increasing order, whereas the individual building blocks do not self-assemble. Subtle structural modifications tune the supramolecular morphologies.
Blocking hypersonic waves by arrays of elongated colloids
Peter J. Beltramo, Dirk Schneider, George Fytas, and Eric M. Furst
Anisotropic Hypersonic Phonon Propagation in Films of Aligned Ellipsoids
Researchers from UDEL and MPIP have fabricated films of aligned ellipsoids using an electric field directed convective self-assembly. These films possess anisotropic elastic mechanical properties and a direction-dependent phononic band gap at hypersonic (GHz) frequencies. The frequency of the gap, which is detected in the direction perpendicular to particle alignment and the effective medium modulus, can be tuned by the particle aspect ratio. The origin of the gap is probably related to the primary eigenvibration of the particle resonating with the effective medium. This first realization reveals the potential for control direction dependent elastic properties by anisotropic particles and self-assembly.
© APS (2014)
Blocking hypersonic waves by arrays of elongated colloids
The diffusion barrier performance of polymeric nanocapsules, and thus their degree of loading, depends on the interactions between the polymer shell and the core material, which can be expressed by the Hansen solubility parameters.
Ines Hofmeister, Prof. Dr. Katharina Landfester and Dr. Andreas Taden
Controlled Formation of Polymer Nanocapsules with High Diffusion-Barrier Properties and Prediction of Encapsulation Efficiency
Polymer nanocapsules with high diffusion-barrier performance were designed following simple thermodynamic considerations. Hindered diffusion of the enclosed material leads to high encapsulation efficiencies (EEs), which was demonstrated based on the encapsulation of highly volatile compounds of different chemical natures. Low interactions between core and shell materials are key factors to achieve phase separation and a high diffusion barrier of the resulting polymeric shell. These interactions can be characterized and quantified using the Hansen solubility parameters. A systematic study of our copolymer system revealed a linear relationship between the Hansen parameter for hydrogen bonding (dh) and encapsulation efficiencies which enables the prediction of encapsulated amounts for any material. Furthermore EEs of poorly encapsulated materials can be increased by mixing them with a mediator compound to give lower overall dh values.
© Wiley (2014)
The diffusion barrier performance of polymeric nanocapsules, and thus their degree of loading, depends on the interactions between the polymer shell and the core material, which can be expressed by the Hansen solubility parameters. Using these parameters, encapsulation efficiencies can be predicted and capsules with high diffusion barriers designed.
 
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