Elke Kraker

An All‐Printed Ferroelectric Active Matrix Sensor Network Based on Only Five Functional Materials Forming a Touchless Control Interface

An All-Printed Ferroelectric Active Matrix Sensor Network Based on Only Five Functional Materials Forming a Touchless Control Interface

Integrated organic electronic based optochemical sensors using polarization filters

A compact, integrated photoluminescence based oxygen and pH sensor, utilizing an organic light emitting device (OLED) as the light source and an organic photodiode (OPD) as the detection unit, is described. The main challenge in such an integrated sensor is the suppression of the excitation light at the detector, which is typically by many orders of magnitude higher in intensity than the emitted fluorescence. In our approach, we refrain from utilizing edge filters which require narrow band excitation sources and dyes with an adequate large Stokes shift. We rather developed an integrated sensor concept relying on two polarizers to separate the emission and excitation light. One polarizer is located right after the OLED, while the other one, oriented at 90° to the first, is placed in front of the OPD. The main advantage of this solution is that any combination of excitation and emission light is acceptable, even if the two signals overlap spectrally. This is especially important for the use of OLEDs as the ...

Diffusion of Ag into Organic Semiconducting Materials: A Combined Analytical Study Using Transmission Electron Microscopy and X-ray Reflectivity

This study shows that the morphology of organic/metal interfaces strongly depends on process parameters and the involved materials. The interface between organic n-type blocking layer materials and the top Ag cathode within an organic photodiode was investigated. Ag was deposited on either amorphous tris-8-hydroxyquinolinato-aluminum (Alq(3)) or crystalline 4,7-diphenyl-1,10-phenanthroline (Bphen) using different deposition techniques such as electron beam deposition, ion beam sputtering, and vacuum thermal evaporation at various deposition rates. The interfaces were studied by transmission electron microscopy and X-ray reflectivity. It was found that Bphen does not show any Ag diffusion no matter which deposition technique was used, whereas the Ag diffusion into Alq(3) depends on the deposition technique and the deposition rate. The highest amount of Ag diffusion into Alq(3) occurred by using thermal vacuum deposition at low deposition rates.

Waveguide-integrated SPR sensing on an all-organic platform

Optoelectronical components and devices based on organic materials offer a wealth of possibilities in terms of integration, miniaturization and potentially low-cost fabrication for relevant applications, notwithstanding a performance that may fall short of conventional state-of-the-art systems. In this context we report on progress towards the combination of surface plasmon resonance (SPR) sensing with a monolithically integrated optical sensor platform based on organic materials, including an organic light emitting diode, an optical polymer waveguide and an organic photo diode. Several according components have been developed and demonstrated recently and were exemplarily applied to fluorescence lifetime detection. Aiming at multianalyte performance we add SPR to this platform, which enables the sensitive, real-time and label-free detection of a wide range of analytes. The SPR detection scheme is based on a gold surface sustaining a surface plasmon mode which reacts sensitively to analyte-induced refractive index changes. Here, we report on the investigation of the sensor response of a 50 nm thick gold film on an 11 μm thick multimode polymer waveguide. The feasibility of this sensor concept is shown and its sensitivity is estimated from measuring the intensity transmitted trough the waveguide at a single wavelength. In addition, some further steps towards full integration are discussed.

Structure and morphology of an organic/inorganic multilayer stack: An x-ray reflectivity study

The internal morphology and crystallographic properties of a complete organic thin film multilayer stack are characterized via x-ray scattering techniques, atomic force microscopy (AFM), and scanning electron microscopy. The stack consists of the three organic layers – copper(II)phthalocyanine (CuPc), perylene tetracarboxylic bisbenzimidazole (PTCBI), and aluminum-tris(8-hydroxychinolin) (Alq3) – sandwiched between an optically semitransparent gold layer and a top silver electrode. The interface roughness progress is determined by the x-ray reflectivity, which is confirmed by the surface roughness determination via AFM. The crystallographic properties are characterized via x-ray diffraction. The CuPc layer is highly crystalline with preferentially oriented crystallites but forms a rough interface (σRMS = 5.5 nm) toward the PTCBI layer. The PTCBI layer grows with randomly distributed crystallites in a worm-like morphology with an interface roughness of σRMS = 6.4 nm toward the Alq3 layer. The amorphous Alq...

Filter-free integrated sensor array based on luminescence and absorbance measurements using ring-shaped organic photodiodes

AbstractAn optical waveguiding sensor array featuring monolithically integrated organic photodiodes as integrated photo-detector, which simplifies the readout system by minimizing the required parts, is presented. The necessity of any optical filters becomes redundant due to the proposed platform geometry, which discriminates between excitation light and sensing signal. The sensor array is capable of measuring luminescence or absorption, and both sensing geometries are based on the identical substrate. It is demonstrated that background light is virtually non-existent. All sensing and waveguide layers, as well as in- and out-coupling elements are assembled by conventional screen-printing techniques. Organic photodiodes are integrated by layer-by-layer vacuum deposition onto glass or common polymer foils. The universal and simple applicability of this sensor chip is demonstrated by sensing schemes for four different analytes. Relative humidity, oxygen, and carbon dioxide are measured in gas phase using luminescence-based sensor schemes; the latter two analytes are also measured by absorbance-based sensor schemes. Furthermore, oxygen and pH in aqueous media were enabled. The consistency of calibration characteristics extending over different sensor chips is verified. FigureIntegrated fluorescence (left) and absorbance (right) based sensor waveguide

Integrated organic optical sensor arrays based on ring-shaped organic photodiodes

We present an integrated optical sensor platform suitable for the parallel detection of multiple parameters in an array format. This sensor technology combines fluorescent sensor layers with ring-shaped thin-film organic photodiodes (OPDs), serving as integrated fluorescence detectors. The sensing layers are deposited by screen-printing on the upper side of a PET substrate, which is exposed to an analyte, whereas the ring-shaped photodiodes are monolithically integrated, by vapour phase deposition, on the backside of the transparent substrate, in correct alignment to the sensing layers. The monolithic integration of sensor layers and detectors on one common substrate as well as the special ring shaped form of the photodiodes guarantees that a maximum of the fluorescent light emitted from the sensor layers is collected. A key advantage of the above described sensor geometry is the straightforward potential to realise sensor arrays for the parallel detection of multiple parameters: different sensor spots are illuminated by commercial LEDs or alternatively with one large area OLED, and are read-out by individual integrated organic photodiodes, surrounding the respective sensor layers. Three different sensing principles including absorption, fluorescence and surface plasmon resonance can be applied in the same basic sensor platform. The functionality of the concept is demonstrated by an integrated oxygen sensor. Sensor schemes for the analytical parameters carbon dioxide, temperature and ammonia, are proposed. Efficient front end electronics enabling intensity and time domain detection of sensor signals for the testing and characterisation of the integrated sensor devices have been developed.

Development of printed ITO coatings on PET and PEN foil for flexible organic photodiodes

ITO (tin doped indium oxide) coatings with a sheet resistance of 2 to 3 kΩ(square) were produced by gravure printing process on PET and PEN foil. The printing paste consisted of ITO nanoparticles which were dispersed in a solvent by using a surfactant. The dispersion was mixed with a binder and a photo initiator before printing. The printed films were hardened under UV-irradiation at low temperatures (< 130°C). The sheet resistance could be decreased by heat treatment at 120°C under forming gas atmosphere (N2/H2) to 1.5 kΩ(square). The transmission of the ITO coated PET and PEN foils is more than 80 % in the visible range. The ITO films were directly used as the bottom electrode in an organic photodiode (OPD). The setup of the OPD originates from the well known Tang photodiode, consisting of a stacked layer of copper phthalocyanine (p-type material) and perylene tetracarboxylic bisbenzimidazole (n-type material). The photodiodes are characterised via current-voltage (I-V) characteristics. The performance of the photodiodes with printed ITO on plastic substrates could be improved by the deposition of a PEDOT/PSS layer (Baytron(R) P) on the ITO coated foils and was then comparable to the performance of photodiodes with semi-transparent gold as anode on PET substrates. These results demonstrate the suitability of the printed ITO layers as anode for organic photodiodes.

Integrated waveguide sensor platform utilizing organic photodiodes

We present a novel waveguide sensor platform, combining monolithically integrated sensor waveguides with thin-film organic photodiodes on a single substrate. Aiming at the parallel detection of multiple parameters in a single sensor chip different sensing principles can be applied on the same basic sensor platform. Utilizing absorbance as sensing principle is demonstrated by an integrated carbon dioxide sensor, fluorescence as sensing principle is demonstrated by an integrated oxygen sensor. The versatility of this integrated waveguide platform is further demonstrated by employing surface plasmon resonance as sensing principle, enabling real-time and label-free detection of a wide range of analytes.

Optochemical sensor based on screenprinted fluorescent sensorspots surrounded by organic photodiodes for multianalyte detection

A compact, integrated photoluminescence based oxygen sensor, utilizing an organic light emitting device (OLED) as the light source and an organic photodiode (OPD) as the detection unit, is described. The detection system of the sensor array consists of an array of circular screen-printed fluorescent sensor spots surrounded by organic photodiodes as integrated fluorescence detectors. The OPD originates from the well-known Tang photodiode, consisting of a stacked layer of copper phthalocyanine (CuPc, p-type material) and perylene tetracarboxylic bisbenzimidazole (PTCBi, n-type material). An additional layer of tris-8-hydroxyquinolinatoaluminium (Alq3, n-type material) was inserted between the PTCBi layer and cathode. An ORMOCERR layer was used as encapsulation layer. For excitation an organic light emitting diode is used. The sensor spot and the detector are processed on the same flexible substrate. This approach not only simplifies the detection system by minimizing the numbers of required optical components - no optical filters have to be used for separating the excitation light and the luminescent emission-, but also has a large potential for low-cost sensor applications. The feasibility of the concept is demonstrated by an integrated oxygen sensor, indicating good performance. Sensor schemes for other chemical parameters are proposed.