Injection-limited and space charge-limited currents in organic semiconductor devices with nanopatterned metal electrodes

Charge injection at metal-organic interfaces often limits the electric current in organic light-emitting diodes without additional injection layers. Integrated nanopatterned electrodes may provide a way to overcome this current injection limit by local field enhancements leading to locally space charge-limited currents. We compare electrical characteristics of planar and nanopatterned hole-only devices based on the charge transport material NPB with different thicknesses in order to investigate the nanopattern's effect on the current limitation mechanism. Integration of a periodic nanograting into the metal electrode yields a current increase of about 1.5-4 times, depending on thickness and operating voltage. To verify the experimental results, we implement a finite element simulation model that solves the coupled Poisson and drift-diffusion equations in a weak form. It includes space charges, drift and diffusion currents, nonlinear mobility, and charge injection at the boundaries. We find in experiment and simulation that the planar devices exhibit injection-limited currents, whereas the currents in the nanopatterned devices are dominated by space charge effects, overcoming the planar injection limit. The simulations show space charge accumulations at the corners of the nanopattern, confirming the idea of locally space charge-limited currents

Signal-to-noise ratio enhanced electrode configurations for magnetoelectric cantilever sensors

Magnetoelectric cantilevers consisting of strain-coupled magnetostrictive and piezoelectric (PE) layers are applicable to magnetic-fi eld sens- ing. For the fi rst bending mode, the magnetic fi eld-induced stress distribution is of equal sign along the cantilever length. Thus, a plate- capacitor electrode configuration encompassing the complete PE layer may be used for collecting the strain-induced charge. For higher order modes, stress regions of the opposite sign occur in the cantilever length direction. To prevent charge cancellation and to harvest the piezo- electric induced charge effi ciently, segmented electrodes are employed. This study investigates the effect of the electrode confi gurationon the signal-to-noise ratio (SNR) for higher order bending modes. The charges collected by the electrodes are calculated using a fi nite element method simulation considering the mechanical, electrical, and magnetic properties of the cantilever. By combination with an analytic noise model, taking into account the sensor and amplifi er noise sources, the SNR is obtained. We analyze a 3 mm long, 1 mm wide, and 50 μm thick silicon cantilever with layers of 2 μm magnetostrictive soft amorphous metal (FeCoSiB) and 2 μm piezoelectric aluminum nitride. We demonstrate that an SNR-optimized electrode design yields an SNR improvement by 2.3 dB and 2.4 dB for the second and third bending modes compared to a signal optimized design

Beamforming OLEDs for sensing applications employing a nanostructured fluorescent waveguide layer

Organic light-emitting diodes (OLEDs) hold great promise as light sources for miniaturized and monolithically integrated optical sensors. Their unique properties and flexible processing methods enable the realization of disposable or recyclable lab-on-a-chip systems by combining multiple light sources and detector units on a single substrate. One of the main challenges in these systems is tailoring of light emission characteristics in order to illuminate specific sensing spots without the use of external optical components. Since OLEDs typically exhibit wide-angle light emission across the device surface, we propose the implementation of a nanostructured fluorescent waveguide. This layer acts as a color conversion filter by absorbing OLED light while providing narrow-angle emission of fluorescent light propagating in the waveguide. The appropriate choice of OLED emission color, fluorescent dye and nanostructure design allows for tailoring of the emission wavelength and beam characteristics. We investigate the impact of various fabrication parameters such as the layer thickness and fluorophore concentration on the color conversion efficiency as well as the directionality of the outcoupled fluorescent light. While high absorption of the OLED excitation light is beneficial in order to suppress wide-angle background emission, we show that high fluorophore content may lead to fluorescence quenching and reabsorption of fluorescent light inside the waveguide impairing resonant outcoupling effects

Resonance‐Based Directional Light Emission from Organic Light‐Emitting Diodes: Comparing Integrated Nanopatterns and Color Conversion Waveguide Gratings

Tailoring the angular emission pattern of organic light-emitting diodes (OLEDs) is a promising approach to increase device performance in many applications. In miniaturized point-of-need sensor systems using organic light sources and photodetectors, directional illumination of specific sensing spots may enhance overall sensitivity by improved light utilization. Periodically nanopatterned waveguides forming photonic crystal slabs are oftentimes employed to obtain directional resonant light outcoupling from OLEDs. This work compares emission directionality for two types of devices utilizing the same polymer compounds as the emissive material: OLEDs comprising a nanopatterned bottom electrode and conventional OLEDs featuring a dedicated nanopatterned color conversion layer (CCL) for directional light outcoupling. Simulated and experimentally measured emission characteristics show that resonant outcoupling effects from a separate CCL are significantly stronger due to spatial separation from the lossy electrode layers as well as high optical contrast at the waveguide interfaces. While OLEDs with nanopatterned electrodes exhibit only small deviations from the Lambertian emission profile, the nanopatterned CCL induces high outcoupling peaks at specific viewing angles leading to increased emission directionality

Psychic Distance and the importance of its perception concerning the management of international processes, of internet-operating companies

In the last decades it has been argued whether psychic distances have lost their importance on the world markets. The access to information through the internet may have reduced them and made them more understandable, but it has also increased the overall world trades leading to more diversity and therefore to more different market segments that have to be considered. This contrary statements are investigated in this master thesis and further evaluates the current importance of psychic distances in relation to the perception of the managers towards it. Therefore it gives an insight into how psychic distances affect the management of a web- based companies called Compare AG. The progress of this work mirrors this discussion along with the development process of the company. It will show how it went from a unexperienced firm, which merely copied their concept to another market expecting it to work, to a company that adapts to the foreign markets and has specialists for every country to cope with any kind of market changes illustrating both opinions on how important psychic distances still are today especially for internet-operating companies

Vergleichende Analyse öffentlicher Rechnungssysteme - Länderberichte, 9 Bde.

Die vorliegenden Berichte sind Teilergebnisse der von der Deutschen Forschungsgemeinschaft geförderten Studie "Vergleichende Analyse öffentlicher Rechnungssysteme". Gegenstand dieser Studie ist das externe Rechnungswesens staatlicher Gebietskörperschaften. Neben dem externen Rechnungswesen selbst wurden auch Informationen zu den nationalen Rahmenbedingungen, zum Budgetierungsverfahren, zu Prüfungspraktiken und zum internen Rechnungswesen erhoben

Vergleichende Analyse öffentlicher Rechnungssysteme - Länderberichte, 9 Bde.

Die vorliegenden Berichte sind Teilergebnisse der von der Deutschen Forschungsgemeinschaft geförderten Studie "Vergleichende Analyse öffentlicher Rechnungssysteme". Gegenstand dieser Studie ist das externe Rechnungswesens staatlicher Gebietskörperschaften. Neben dem externen Rechnungswesen selbst wurden auch Informationen zu den nationalen Rahmenbedingungen, zum Budgetierungsverfahren, zu Prüfungspraktiken und zum internen Rechnungswesen erhoben