1,216 research outputs found
Non-innocent side-chains with dipole moments in organic solar cells improve charge separation
Providing sustainable energy is one of the biggest challenges nowadays. An attractive answer is the use of organic solar cells to capture solar energy. Recently a promising route to increase their efficiency has been suggested: developing new organic materials with a high dielectric constant. This solution focuses on lowering the coulomb attraction between electrons and holes, thereby increasing the yield of free charges. In here, we demonstrate from a theoretical point of view that incorporation of dipole moments in organic materials indeed lowers the coulomb attraction. A combination of molecular dynamics simulations for modelling the blend and ab initio quantum chemical calculations to study specific regions was performed. This approach gives predictive insight in the suitability of new materials for application in organic solar cells. In addition to all requirements that make conjugated polymers suitable for application in organic solar cells, this study demonstrates the importance of large dipole moments in polymer side-chains
Resonances and Twist in Volume-Preserving Mappings
The phase space of an integrable, volume-preserving map with one action and
angles is foliated by a one-parameter family of -dimensional invariant
tori. Perturbations of such a system may lead to chaotic dynamics and
transport. We show that near a rank-one, resonant torus these mappings can be
reduced to volume-preserving "standard maps." These have twist only when the
image of the frequency map crosses the resonance curve transversely. We show
that these maps can be approximated---using averaging theory---by the usual
area-preserving twist or nontwist standard maps. The twist condition
appropriate for the volume-preserving setting is shown to be distinct from the
nondegeneracy condition used in (volume-preserving) KAM theory.Comment: Many typos fixed and notation simplified. New order
averaging theorem and volume-preserving variant. Numerical comparison with
averaging adde
Liquid crystal device
The invention relates to a device comprising at least one substrate, an electrode structure and a liquid crystalline polymer film obtainable from a polymerisable LC medium comprising one or more multi-or direactive or monoreactive mesogenic compounds, characterized in that the surface shape of said polymer film can be electrically switched. Furthermore, the invention relates to a process of production of said device, to the use of said device in an electro-opticalor electro-mechanical device and to an electro-opticalor electro-mechanical device comprising said device
Liquid crystal device
The invention relates to a device comprising at least one substrate, an electrode structure and a liquid crystalline polymer film obtainable from a polymerisable LC medium comprising one or more multi-or direactive or monoreactive mesogenic compounds, characterized in that the surface shape of said polymer film can be electrically switched. Furthermore, the invention relates to a process of production of said device, to the use of said device in an electro-opticalor electro-mechanical device and to an electro-opticalor electro-mechanical device comprising said device
Circular dichroism of cholesteric polymers and the orbital angular momentum of light
We explore experimentally if the light's orbital angular momentum (OAM)
interacts with chiral nematic polymer films. Specifically, we measure the
circular dichroism of such a material using light beams with different OAM. We
investigate the case of strongly focussed, non-paraxial light beams, where the
spatial and polarization degrees of freedom are coupled. Within the
experimental accuracy, we cannot find any influence of the OAM on the circular
dichroism of the cholesteric polymer.Comment: 3 pages, 4 figure
On the relation between local and charge-transfer exciton binding energies in organic photovoltaic materials
In organic photovoltaic devices two types of excitons can be generated for which different binding energies can be defined: the binding energy of the local exciton generated immediately after light absorption on the polymer and the binding energy of the charge-transfer exciton generated through the electron transfer from polymer to PCBM. Lowering these two binding energies is expected to improve the efficiency of the devices. Using (time-dependent) density functional theory, we studied whether a relation exists between the two different binding energies. For a series of related co-monomers, we found that the local exciton binding energy on a monomer is not directly related to that of the charge-transfer exciton on a monomer-PCBM complex because the variation in exciton binding energy depends mainly on the variation in electron affinity, which does not affect in a direct way the charge-transfer exciton binding energy. Furthermore, for the studied co-monomers and their corresponding trimers, we provide detailed information on the amount of charge transfer upon excitation and on the charge transfer excitation length. This detailed study of the excitation process reveals that the thiophene unit that links the donor and acceptor fragments of the co-monomer actively participates in the charge transfer process
Resonances in a spring-pendulum: algorithms for equivariant singularity theory
A spring-pendulum in resonance is a time-independent Hamiltonian model system for formal reduction to one degree of freedom, where some symmetry (reversibility) is maintained. The reduction is handled by equivariant singularity theory with a distinguished parameter, yielding an integrable approximation of the Poincaré map. This makes a concise description of certain bifurcations possible. The computation of reparametrizations from normal form to the actual system is performed by Gröbner basis techniques.
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