Bipolar charge transport in organic field-effect transistors: Enabling high mobilities and transport of photo-generated charge carriers by a molecular passivation layer

High mobility bipolar charge carrier transport in organic field-effect transistors (OFETs) can be enabled by a molecular passivation layer and selective electrode materials. Using tetratetracontane as passivation layer bipolar transport was realised in the organic semiconductors copper-phthalocyanine, diindenoperylene, pentacene, TIPS-pentacene and sexithiophene and mobilities of up to 0.1 cm²/V s were achieved for both electrons and holes. Furthermore, the trap and injection behaviour was analysed leading to a more general understanding of the transport levels of the used molecular semiconductors and their limitations for electron and hole transport in OFETs. With this knowledge the transistor operation can be further improved by applying two different electrode materials and a light-emitting transistor was demonstrated.Additionally, the effect of illumination on organic field-effect transistors was investigated for unipolar and bipolar devices. We find that the behaviour of photo-excited electrons and holes depends on the interface between the insulator and the semiconductor and the choice of contact materials. Whereas filling of electron traps by photo-generated charges and the related accumulation field are the reason for changes in charge carrier transport upon illumination without passivation layer, both types of charge carriers can be transported also in unipolar OFETs, if a passivation layer is present.     

Performance of 26650 Li-ion cells at elevated temperature under simulated PHEV drive cycles

Cylindrical (type: 26650) Li-ion cells (LiFePO₄ cathodes) currently used in the electric vehicles (EVs), plug-in hybrid electric vehicles etc. were subjected to simulated federal urban driving schedule at 25 and 50 °C for performance evaluation. Drive profiles (current versus time) for charge sustaining and charge depleting modes were derived from the federal urban driving schedule velocity profiles considering acceleration, regenerative braking, rolling resistance, drag force etc. for typical plug-in hybrid electric vehicles. In particular, the batteries were cycled extensively at 50 °C under charge sustaining as well as charge depleting modes to monitor capacity values, followed by analyzing the LiFePO₄ cathode material by X-ray diffraction analysis. The capacity degradation was found to be very significant in both the modes with 13 and 19% under charge sustaining and charge depleting modes after 337 and 1007 cycles, respectively at elevated temperature. High frequency resistance values measured by electrochemical impedance spectroscopy were found to increase significantly under high temperature cycling, leading to power fading. As evident from Rietveld analysis, phase change in LiFePO₄ is observed beyond 1000 cycles at elevated temperature under charge depleting mode, with the observation of FePO₄ from the powder diffraction data of the cathodes from the cycled cells. In addition, there was also significant change in crystallite size of the cathode active materials after charge/discharge cycling under charge depleting mode.     

Zusätzliche Sicherheitsaspekte des Mehrlagenbehälters

Additional safety aspects of coiled-layer containers . The coiled-layer construction technique has a number of particular safety engineering advantages over solid construction methods which are characterized by the following features: (1) Each kind of stress in a container is directed to a shell specially designed for this kind of stress. (2) A planned arrangement of welding seams minimises weakening. (3) The containers can be constantly monitored. (4) Failures remain under control owing to the possibility of constant monitoring. Examples and experiments are reported for the Krupp coiled-layer construction method.     

First realized polarization converter based on hybrid supermodes

We report the first realized polarization converter based on the concept of hybrid supermodes. A polarization conversion of 93% is achieved for a device length of only 0.25 mm. This represents the shortest polarization converter realized on InP so far     

Bilateral radial deficiency with lower limb involvement

We describe a 10-month-old boy with an unclassified form of radial aplasia with absent thumbs, tibia hypo/-aplasia, and partial absence of toes. Only a few cases with similar limb deficiencies have been published. We try to classify the malformations on the basis of embryological considerations and discuss possible differential diagnosis.     

Effects of reperfusion on arrhythmias and death after coronary artery occlusion in the rat: increased electrical stability independent of myocardial salvage

OBJECTIVES: This study sought to delineate salvage-dependent from salvage-independent coronary reperfusion in acute myocardial infarction and the effects on spontaneously occurring arrhythmias and arrhythmic death in rats. BACKGROUND: Reperfusion of the infarct-related artery might increase electrical stability independently of salvage of ischemic myocardium. METHODS: In 98 conscious rats the electrocardiogram was monitored by telemetry for 48 h after MI, and all episodes of ventricular tachycardia (VT) and ventricular fibrillation (VF) were analyzed. Reperfusion at 45 min (RP45) (n = 15), 90 min (RP90) (n = 18) and 180 min (RP180) (n = 30) min was compared with permanent coronary artery occlusion (CAO) (n = 35) with respect to the post-reperfusion periods. RESULTS: RP45, RP90 and RP180 reduced the incidence of VT by 93%, 98% and 88% and VF by 89%, 97% and 92%, respectively (all p < 0.01 vs. CAO). The all-cause mortality rate was reduced from 47% (CAO) to 8% (RP45, p < 0.05) and 0% (RP90, p < 0.01); after RP180 it was 17% (CAO 42%, p = 0.08). All reperfusion regimens reduced arrhythmic deaths: 47% to 8% (RP45, p < 0.05), 47% to 0% (RP90, p < 0.01) and 42% to 8% (RP180, p < 0.05). Infarct size was identical to that during CAO (49 +/- 10% [mean +/- SD]) and RP180 (49 +/- 10%), whereas preferentially epicardial salvage occurred at RP45 (36 +/- 8%, p < 0.001) and RP90 (38 < 10%, p < 0.001). CONCLUSIONS: Early and late reperfusion reduce the incidence and duration of VT and VF in conscious rats with acute MI. Thereby, arrhythmia-related mortality is improved through the prevention of fatal VF episodes. Thus, reperfusion increases the electrical stability of the heart independently of myocyte salvage, as proposed by the open artery hypothesis.     

Software-Industrialisierung

SOFTWARE-INDUSTRIALISIERUNG

Software-Industrialisierung     

Enhanced properties of poly(ε-caprolactone)/polyvinylpyrrolidone electrospun scaffolds fabricated using 1,1,1,3,3,3-hexafluoro-2-propanol

Poly(ε-caprolactone)/polyvinylpyrrolidone (PCL/PVP) scaffolds with various composition were fabricated from 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) solution using the same electrospinning parameters in order to reveal the effect of polymer ratio on the material properties. The obtained materials were characterized using scanning electron microscopy, contact angle measurements, X-ray diffraction, Fourier-transformed infrared spectroscopy, and tensile testing. The strengthening effect of PVP was observed: Young modulus of PCL/PVP scaffold with 50/50 polymer ratio was found at 105.4 ± 8.4 MPa which is six times higher comparing to those of PCL scaffold. PVP-containing scaffolds were extremely hydrophilic with PVP concentration of 5 wt% (vs. 25 wt% in previous reports) leading to full wetting of the material. in vitro studies showed an improved viability of HeLa cells cultured with the composites containing higher concentrations of PVP. Owing to the application of HFIP, PCL-based materials were loaded with cyclophosphamide for the first time and the PVP-containing materials demonstrated the intensified initial release of the model compound. Utilizing HFIP for the fabrication of PCL/PVP scaffolds significantly widens their application for drug delivery systems due to a good solubility of proteins, drugs, and other biologically active compounds in this solvent.     

UV‐Light‐Driven Oxygen Pumping in a High‐Temperature Solid Oxide Photoelectrochemical Cell

A solid‐state photoelectrochemical cell is operated between 400 and 500 °C under 365 nm UV light. The cell consists of a photovoltaic part, based on a La_0.8Sr_0.2CrO₃/SrTiO₃ junction, and an electrochemical part including a zirconia solid electrolyte with a shared (La,Sr)FeO₃ electrode. The photovoltaic cell part leads to open circuit voltages up to 920 mV at 400 °C. Upon UV light, this driving force is used in the electrochemical part of the cell to pump oxygen from low to high partial pressures, i.e., to convert radiation energy to chemical energy. This demonstrates the feasibility of high‐temperature photoelectrochemical cells for solar energy storage. The detailed characterization of the different resistance contributions in the system by DC and AC methods reveals the parts of the cell to be optimized for finally achieving high‐temperature photoelectrochemical water splitting.