Emil J. W. List-Kratochvil

Organic Non‐Volatile Resistive Photo‐Switches for Flexible Image Detector Arrays

A unique implementation of an organic image detector using resistive photo-switchable pixels is presented. This resistive photo-switch comprises the vertical integration of an organic photodiode and an organic resistive switching memory element. The photodiodes act as a photosensitive element while the resistive switching elements simultaneously store the detected light information.

Unravelling the Nature of Unipolar Resistance Switching in Organic Devices by Utilizing the Photovoltaic Effect

The origin of resistive switching in organic devices is studied by photovoltaic methods and impedance spectroscopy. The results show that the most commonly proposed charging/discharging mechanisms can be excluded as working mechanism. There is solid evidence that resistive switching is due to the formation/rupture of filaments. Further, it is shown that this is a universal property of metal/organic/metal thin-film devices.

Electrolyte‐Gated Organic Field‐Effect Transistor for Selective Reversible Ion Detection

An ion-sensitive electrolyte-gated organic field-effect transistor for selective and reversible detection of sodium (Na(+) ) down to 10(-6) M is presented. The inherent low voltage - high current operation of these transistors in combination with a state-of-the-art ion-selective membrane proves to be a novel, versatile modular sensor platform.

Simultaneous extraction of charge density dependent mobility and variable contact resistance from thin film transistors

A model for the extraction of the charge density dependent mobility and variable contact resistance in thin film transistors is proposed by performing a full derivation of the current-voltage characteristics both in the linear and saturation regime of operation. The calculated values are validated against the ones obtained from direct experimental methods. This approach allows unambiguous determination of gate voltage dependent contact and channel resistance from the analysis of a single device. It solves the inconsistencies in the commonly accepted mobility extraction methods and provides additional possibilities for the analysis of the injection and transport processes in semiconducting materials.

Direct observation of conductive filament formation in Alq3 based organic resistive memories

This work explores resistive switching mechanisms in non-volatile organic memory devices based on tris(8-hydroxyquinolie)aluminum (Alq3). Advanced characterization tools are applied to investigate metal diffusion in ITO/Alq3/Ag memory device stacks leading to conductive filament formation. The morphology of Alq3/Ag layers as a function of the metal evaporation conditions is studied by X-ray reflectivity, while depth profile analysis with X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry is applied to characterize operational memory elements displaying reliable bistable current-voltage characteristics. 3D images of the distribution of silver inside the organic layer clearly point towards the existence of conductive filaments and allow for the identification of the initial filament formation and inactivation mechanisms during switching of the device. Initial filament formation is suggested to be driven by field assisted diffusion of silver from abundant structures formed during the top electrode evaporation, whereas thermochemical effects lead to local filament inactivation.

Integrated catheter system for continuous glucose measurement and simultaneous insulin infusion

A new measurement system enables combination of continuous glucose monitoring (CGM) and insulin infusion. A sensor system comprising an optical glucose biosensor and an optical oxygen sensor is integrated into the insulin infusion catheter of an insulin pump. Both sensors rely on near infrared (NIR) phosphorescent porphyrin dyes, wherefore the signals can be read out transcutaneous and non-invasively with a custom-built phase fluorometer measurement module. The spectral properties of the indicator dyes and the optical setup of the measurement module were optimized to enable independent read-out in two channels. Dynamic ranges from 0 mmHg to 160 mmHg oxygen and 0mg/dL to 360 mg/dL glucose (LOD 2mg/dL) are covered by the oxygen and the glucose sensor, respectively. In-vivo measurements in pigs demonstrate good correlation of reference blood glucose levels and glucose values obtained with the presented sensor system. The evaluation of the clinical accuracy of the system with Clarke Error Grid Analysis showed similar results to CGM-devices currently on the market.

Hydrogen ion-selective electrolyte-gated organic field-effect transistor for pH sensing

A H+ ion-selective electrolyte-gated organic field-effect transistor (IS-EGOFET) with a broad detection range between pH 3 and pH 12, is presented. This pH sensor relies on an integrated EGOFET used as a transducer in combination with an ionophore-doped polymeric ion-selective membrane serving as a sensing element. The broad detection range was possible through a dynamic measurement protocol comprising a readjustment of the gate voltage, which ensures a stable device operation at a constant working point. The effectiveness of this dynamic approach is confirmed by stability investigations. On the basis of this pH sensor concept, the importance of an appropriate gating electrolyte is highlighted, giving insights into the working mechanism of EGOFETs.

High performance indium tin oxide-free solution-processed organic light emitting diodes based on inkjet-printed fine silver grid lines

We report on the grid design requirements and inkjet-printing processing conditions of well-defined silver nanoparticles combined with poly(3,4-ethylenedioxylthiophene):poly(styrenesulfonate) PEDOT:PSS as indium tin oxide (ITO) replacement for ITO-free organic light emitting diodes (OLEDs). Solution-processed ITO-free OLEDs based on the 5BTF8 blend of poly(9,9-dioctylfluorene-alt-benzothiadiazole (F8BT) and poly(9,9-di-n-octylfluorenyl-2,7-diyl) (PFO) light-emitting layers, processed in ambient conditions, showed comparable luminance efficiency and power efficiency values to reference devices based on ITO and near identical efficiencies at low luminance values.

Inkjet-printed embedded Ag-PEDOT:PSS electrodes with improved light out coupling effects for highly efficient ITO-free blue polymer light emitting diodes

We report on solution processed polymer light emitting diodes (PLEDs) using inkjet-printed embedded and non-embedded metal grid anodes. Metal grids were inkjet-printed in a honeycomb layout. Honeycomb dimensions were varied from 3 mm to 8 mm to optimize device performance. Inkjet-printed grids were then coated with a highly conductive PEDOT:PSS formulation. First experiments on PEDOT:PSS coated, non-embedded metal grid anodes showed that grids with a 3 mm honeycomb diameter have a similar efficiency as optimized indium tin oxide (ITO) based reference devices. To further improve the efficiency of the devices, the honeycomb Ag-grids were embedded in an Ormocer®-based material. A detailed performance analysis of PLEDs fabricated on ITO, non-embedded and embedded grids was carried out. It is shown that reduced leakage current and enhanced light outcoupling by embedding result in a significant efficiency enhancement of 250% in inkjet-printed embedded Ag-PEDOT:PSS ITO-free PLEDs, compared to the ITO-based refer...

A silver inkjet printed ferrite NFC antenna

This paper presents a near field communication (NFC) antenna that is printed directly on a ferrite substrate using a silver inkjet printing process. Such a silver inkjet printed ferrite NFC antenna provides a minimum substrate thickness, a good operation on metal objects, and a small assembly effort. The NFC antenna performance is analysed by measurements based on the ISO/IEC standard 10373-6 for proximity identification cards test methods. For this, the antenna is connected to an NFC microchip. Measurements in a non-metal environment show that the ferrite antenna performs equally good a custom-built NFC antenna printed on photo paper substrate, despite additional losses in the ferrite substrate. In a metal environment the ferrite antenna clearly outperforms the photo paper antenna.