1,721,238 research outputs found
Excitons dominate the emission from PM6
No full textNon-fullerene acceptors (NFAs) are far more emissive than their fullerene-based counterparts. Here, we study the spectral properties of photocurrent generation and recombination of the blend of the donor polymer PM6 with the NFA Y6. We find that the radiative recombination of free charges is almost entirely due to the re-occupation and decay of Y6 singlet excitons, but that this pathway contributes less than 1% to the total recombination. As such, the open-circuit voltage of the PM6:Y6 blend is determined by the energetics and kinetics of the charge-transfer (CT) state. Moreover, we find that no information on the energetics of the CT state manifold can be gained from the low-energy tail of the photovoltaic external quantum efficiency spectrum, which is dominated by the excitation spectrum of the Y6 exciton. We, finally, estimate the charge-separated state to lie only 120 meV below the Y6 singlet exciton energy, meaning that this blend indeed represents a high-efficiency system with a low energetic offset
Layer Reduces Nonradiative Losses in Organic Solar Cells”
No full textJ.B. acknowledges the Sachsische Aufbaubank through project 100325708 (Infrakart). M.N. acknowledges funding from the Academy of Finland through project 326000. M.P. acknowledges the Deutsche Akademische Austausch Dienst for the Study Completion Scholarship (April-June 2019). The authors thank Prof. Dr. Koen Vandewal from the University of Hasselt, Belgium, for his input and fruitful discussions, as well as Dr. Oskar Sandberg for fruitful discussions and for providing the drift-diffusion simulations. Stephanie Anna Buchholtz and Carsten Habenicht are kindly acknowledged for the UPS measurements
ZAG Expression in Adipose Tissue of Tumour Patients
No full textZAG ist ein Adipokin, dessen Expression in Zusammenhang mit der Kachexie bei Tumorpatienten gebracht wird. Es stimuliert die Lipolyse in Adipozyten, was zu einem Verbrauch der Fettreserven führen kann. In der vorliegenden Untersuchung sollte der Nachweis der ZAG-Genexpression aus reifen, menschlichen Adipozyten geführt werden. Zudem wurde auf RNA Ebene die ZAG Expression im Fettgewebe von Tumorpatienten und Kontrollpersonen untersucht und dabei die Assoziation zwischen der ZAG-Expression, Tumorstadium, Fettzellgröße, und BMI beschrieben.ZAG is an adipokine which is considered to be involved in tumour associated cachexia. It stimulates lipolysis in adipocytes which may lead to a loss of adipose tissue. The following research compared the ZAG expression in adipose tissue from healthy adults and patients with gastrointestinal tumours. On RNA level, the results describe a correlation between the ZAG expression and age, stage of tumour, size of fat cells, the body mass index, and body weight
Influence of the -1051 G/A vWF polymorphism on the clinical outcome after coronary stenting
Full text linkHohe vWF Konzentrationen im Plasma sind mit kardiovaskulären Erkrankungen assoziiert. Das G Allel des -1051 G/A Polymorphismus steht im Zusammenhang mit erhöhten vWF Plasmakonzentrationen. In der vorliegenden Arbeit wurde der Einfluss des -1051 G/A vWF Polymorphismus auf den klinischen Verlauf nach koronarer Stentimplantation untersucht. Der -1051 G/A Genotyp wurde bei 1850 konsekutiven Patienten mit koronarer Herzerkrankung und koronarer Stentimplantation bestimmt. Die klinischen Ereignisse wurden innerhalb von einem Jahr nach der Intervention verfolgt. Bei 84% der Patienten wurde eine Kontrollkoronarangiographie 6 Monate nach Stentimplantation durchgeführt. In dieser Studie konnte weder eine Assoziation zwischen dem -1051GG Genotyp des vWF Gens und einem erhöhten Risiko einer thrombotischen Frühkomplikation, noch dem vermehrten Auftreten einer Restenose nach koronarer Stentimplantation festgestellt werden.High levels of vWF in plasma have been associated with cardiovascular disease. The G allel of the-1051 G/A polymorphism was associated with higher plasma vWF levels. In this study we examined the influence of the -1051G/A polymorphism on the clinical outcome after coronary stenting. The -1051 G/A genotype had been determined in 1850 patients with CAD who had been treated with stent implantation. The clinical outcome had been followed up to one year after intervention. With 84% of the patients we did a control angiography after 6 months. In this study there was no association between the -1051 GG genotype of the vWF gene and a higher risk of developing an early thrombotic lesion or restenosis after coronary stenting
Synaptische Physiologie des sich entwickelnden neuromuskulären Systems von <i>Drosophila</i>
No full textWährend der Entwicklung von sowohl vertebraten, wie auch invertebraten Nervensystemen, ist eine bedeutende Zunahme der Zahl der Synapsen und eine konstante strukturelle und funktionelle Veränderung schon etablierter synaptischer Verbindungen zu verzeichnen. Spezielle Formen solcher synaptischer Modifikationen werden allgemein als essenzielle Bestandteile von Lernprozessen erachtet, und die Stabilisierung dieser Modifikationen erscheint wichtig für die Konsolidierung erlangter Information, in anderen Worten, für das Gedächtnis. In diesem Zusammenhang ist es unklar, wie ein Neuron ein Entwicklungssignal oder ein aktivitätsabhängiges Signal in eine moderate, jedoch physiologisch relevante funktionelle oder strukturelle Veränderung der synaptischen Verbindung übersetzt.Während der Entwicklung des neuromuskulären Systems von Drosophila melanogaster tritt eine hohe Rate an strukturellen und funktionellen Modulierungen der glutamatergen synaptischen Verbindungen auf. Die hier beschriebenen Arbeiten nutzen dieses Merkmal, um Fälle zu untersuchen, in denen die Funktion von Poteinen gestört wird, welche bei der synaptischen Aktivität eine Rolle spielen. Insbesondere wurden elektrophysiologische Analysen durchgeführt, um zu beurteilen, wie die synaptische Physiologie auf solche Manipulationen reagiert. Auf diese Weise konnten die Rollen ausgewählter Proteine für die synaptische Leistung hergeleitet werden, was zu unserem Verständnis des Systems beiträgt.Die beschriebenen Resultate wurden durch Fallstudien über Proteine erlangt, die an prä-, post- und perisynaptischer Funktion teilhaben. (1) Das neu entdeckte Protein Bruchpilot ist von essentieller Bedeutung sowohl für die strukturelle, als auch für die funktionelle Integrität von aktiven Zonen. Indem Bruchpilot die Nähe von Kalziumkanälen zu Vesikeln herstellt, bewirkt es die effiziente Freisetzung von Neurotransmittern und ermöglicht spezifische synaptische Plastizitätsmuster. (2) Die funktionellen Eigenschaften und die unterschiedlichen Effekte der ionotropen Glutamatrezeptor-Untereinheiten GluRIIA und IIB auf synaptische Wirksamkeit werden beschrieben. (3) Schließlich wird das neue perisynaptische Protein Basigin vorgestellt. Basigin trägt zu der Integrität des präsynaptischen Aktinzytoskeletts und der Präzision synchronisierter Freisetzung von Neurotransmittern bei. Die Ergebnisse der Untersuchung veranschaulichen die Beteiligung dieser Proteine an grundlegender synaptischer Leistung. Darüber hinaus implizieren sie den Gebrauch der funktionalen Pfade dieser Proteine, welche die Vorraussetzung für die Umsetzung struktureller und funktioneller synaptischer Entwicklung und Plastizität schaffen.There is a large increase in the number of synapses, and a constant structural and functional remodelling of already established synaptic sites, during the development of both the vertebrate and invertebrate nervous systems. Particular forms of such synaptic modifications are regarded as essential for learning processes, and the stabilisation of such modulations is believed to mediate the consolidation of acquired information, in other words - memory. In this context, it remains unclear how a neuron translates a developmental or activity-dependent signal into a moderate but physiologically relevant alteration in functional or structural synaptic connectivity.Throughout the development of the Drosophila melanogaster neuromuscular junction (NMJ), structural and functional remodelling of glutamatergic synaptic connections takes place at high rates. The work described in this thesis exploits this feature, by examining situations where proteins implicated in synaptic function are interfered with. More specifically, electrophysiological analyses were performed to assess how the synaptic physiology responds to such manipulations. Thereby, the role of candidate proteins in synaptic performance could be deduced, adding to our understanding of the system.The results described were obtained in several case studies of proteins involved in pre-, post-, and perisynaptic function. (1) The novel presynaptic protein Bruchpilot is essential for both the structural and functional integrity of active zones. By establishing proximity between calcium channels and vesicles Bruchpilot promotes efficient neurotransmitter release and enables patterned synaptic plasticity. (2) The functional properties and differential effects of the postsynaptic ionotropic glutamate receptor subunits GluRIIA and IIB on synaptic efficacy are described. And finally, (3) the novel perisynaptic immunoglobulin domain-containing protein Basigin is introduced. Basigin contributes to the integrity of the presynaptic actin cytoskeleton, and to the precision of synchronised neurotransmitter release. The results not only illustrate a role of these proteins in basic synaptic performance, but also imply the recruitment of their functional pathways, required for mediating processes of structural and functional synaptic development and plasticity
Dispersive and steady-state recombination in organic disordered semiconductors
No full textCharge carrier recombination in organic disordered semiconductors is strongly influenced by the thermalization of charge carriers in the density of states (DOS). Measurements of recombination dynamics, conducted under transient or steady-state conditions, can easily be misinterpreted when a detailed understanding of the interplay of thermalization and recombination is missing. To enable adequate measurement analysis, we solve the multiple-trapping problem for recombining charge carriers and analyze it in the transient and steady excitation paradigm for different DOS distributions. We show that recombination rates measured after pulsed excitation are inherently time dependent since recombination gradually slows down as carriers relax in the DOS. When measuring the recombination order after pulsed excitation, this leads to an apparent high-order recombination at short times. As times goes on, the recombination order approaches an asymptotic value. For the Gaussian and the exponential DOS distributions, this asymptotic value equals the recombination order of the equilibrated system under steady excitation. For a more general DOS distribution, the recombination order can also depend on the carrier density, under both transient and steady-state conditions. We conclude that transient experiments can provide rich information about recombination in and out of equilibrium and the underlying DOS occupation provided that consistent modeling of the system is performed
Charge mobility determination by current extraction under linear increasing voltages: Case of nonequilibrium charges and field-dependent mobilities
No full textThe method of current extraction under linear increasing voltages (CELIV) allows for the simultaneous determination of charge mobilities and charge densities directly in thin-film geometries as used in organic photovoltaic (OPV) cells. It has been specifically applied to investigate the interrelation of microstructure and charge-transport properties in such systems. Numerical and analytical calculations presented in this work show that the evaluation of CELIV transients with the commonly used analysis scheme is error prone once charge recombination and, possibly, field- dependent charge mobilities are taken into account. The most important effects are an apparent time dependence of charge mobilities and errors in the determined field dependencies. Our results implicate that reports on time-dependent mobility relaxation in OPV materials obtained by the CELIV technique should be carefully revisited and confirmed by other measurement methods
Impact of Triplet Excited States on the Open-Circuit Voltage of Organic Solar Cells
No full textThe best organic solar cells (OSCs) achieve comparable peak external quantum efficiencies and fill factors as conventional photovoltaic devices. However, their voltage losses are much higher, in particular those due to nonradiative recombination. To investigate the possible role of triplet states on the donor or acceptor materials in this process, model systems comprising Zn- and Cu-phthalocyanine (Pc), as well as fluorinated versions of these donors, combined with C-60 as acceptor are studied. Fluorination allows tuning the energy level alignment between the lowest energy triplet state (T-1) and the charge-transfer (CT) state, while the replacement of Zn by Cu as the central metal in the Pcs leads to a largely enhanced spin-orbit coupling. Only in the latter case, a substantial influence of the triplet state on the nonradiative voltage losses is observed. In contrast, it is found that for a large series of typical OSC materials, the relative energy level alignment between T-1 and the CT state does not substantially affect nonradiative voltage losses
Thermodynamic theory of light-induced material transport in amorphous azobenzene polymer films
No full textIt was discovered 10 years ago that the exposure of an initially flat layer of an azobenzene-containing polymer to an inhomogeneous light pattern leads to the formation of surface relief structures, accompanied by a mass transport over several micrometers. However, the driving force of this process is still unclear. We propose a new thermodynamic approach that explains a number of experimental findings including the light-induced deformation of free-standing films and the formation of surface relief gratings for main inscription geometries. Our basic assumption is that under homogeneous illumination, an initially isotropic sample should stretch itself along the polarization direction to compensate the entropy decrease produced by the photoinduced reorientation of azobenzene chromophores. The magnitude of the elastic stress, estimated by taking the derivative of the free energy over the sample deformation, is shown to be sufficient to induce plastic deformation of the polymer film. Orientational distributions of chromophores predicted by our model are compared with those deduced from Raman intensity measurement
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