Display Technologies

Sensing and Environment

Organic Electronics

Display Technologies

Fast LC

In this project our research focuses on improving the response speed of LC materials and the contrast of LC displays.The current display technologies require displays with high brightness and contrast, low power consumption, and very fast response times, > 5ms. Ways to improve the response speeds of LC materials can be classified into different groups. One method includes the development of very fast LC mixtures. In an other method additives such as fine tuned organic bent core materials can be mixed to the existing liquid crystals to change the viscosity of the system for faster response without effecting other parameters such as contrast. Finally, the polyimid materials which are used to align the liquid crystals can be designed and optimized such that besides providing an excellent contrast ratio by promoting very low off-state transmission to the display, they can also give pre-tilt to the LC materials and the response speeds can be improved.  In MSL beside working on all these three areas to achive very fast response LCDs, we also develop display material characterization softwares.

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Sensing and Environment

Chemiresistive Senors

Objective of the chemiresistive sensor project is the development of nanometer thick stimuli responsive 3D metal-nanoparticle/organic networks. Such networks are chemo-responsive materials, implying that they change their physical or chemical properties on contact with gases, vapors or liquids. Thus, such particle systems have a potential application as highly selective and sensitive chemical sensors.

Within the networks the metal nanoparticles enable the electrical conduction of the material. However, the exact conductivity of the networks is mainly determined by the electronic properties of the organic linker and the contact of the molecule to the nanoparticles. The metal-molecule contact can be tuned by selection of appropriate metal nanoparticles and of the functional groups of the linker molecules. In this regard, a broad library of metal nanoparticles and organic linker molecules was developed, which allowed the creation of tailored stimuli-response networks.

The conductivity measurements are the basis of the investigation of the sensing properties of the material. Other film characterization techniques include optical spectroscopy, XPS, AFM, SEM and TEM measurements. The sensing performance of the networks is characterized upon dosing them with different amounts of target analytes and studying how the electronic or optical properties of the network change due to analyte sorption. In parallel, the mass uptake capability of the network is characterized by performing microgravimetry measurements. The correlation of the results with smart selection of organic molecules gives an insight in the sensing mechanism of such a sensor.

Enzyme Based Sensors

The motivation of the Enzyme Based Sensor project is it to develop a point-of-care device for complex gas samples in the field of healthcare and environment. Exemplary we are working on a biosensor for thiol detection in liquid phase as well as in gas phase. Important issues in this project are the selection of promising enzymes and surfaces, a good protein-surface contact, a protective coating for the enzyme and an optimized readout technique. With the enzyme approach we want to complement the Chemiresistive Sensors to fulfill in cooperation the needs in selectivity and sensitivity.

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Organic Electronics

Logic and Memory Architectures
The project "Logic and Memory Architectures" (LMA) addresses the question of integrating molecular electronic devices. The project consists of different aspects: a dedicated printing technology for the deposition of the top electrode is developed, organic and hybrid materials in thin films are evaluated as diodes or switches, different concepts are proposed for the combination of molecular electronics with CMOS and these concepts are assessed regarding the possible integration density, power consumption and speed.

Design of Molecular Devices
The "Design of Molecular Devices" (DMD) project mainly engages in the design, synthesis, and characterization of molecular materials that can be applied to provide functions, such as rectification or switching, in electronic components. The ongoing trend towards electronic devices having reduced feature sizes emphasizes a concurrent requirement for extremely thin active layers. Self-assembled monolayers (SAMs) are of great interest for this purpose since they can be deposited by simple solution techniques onto a variety of metal surfaces. Our interest in molecular scale electronics relies on the fact that molecules can be synthesized in a defined way, having in-built structural characteristics that translate into an equally defined electrical response (Rectification, NDR, bistability). The expertise in chemical synthesis is thus exploited for realization of molecular building blocks that, due to their electrical response, potentially constitute the base of future molecular electronics materials.

Key objectives of the DMD project are identifying and optimizing the factors that control charge transport across metal-molecule and molecule-molecule junctions. This work is focused on three main topics: integration of functionality into the molecular structure, optimization of the binding chemistry and the deposition method of organic layers on metal surfaces, and the electrical characterization of molecular devices.

Dye-Sensitized Solar Cell (DSSC):

Dye-Sensitized Solar Cell (DSSC) is a relatively new photovoltaic technology which imitates the way plants convert sunlight into energy, with the difference that in plants the light is converted into chemical energy (glucose) whereas in the DSSC it is converted into electrical energy. DSSC has a thin sandwich-type geometry comprising a porous film of nanometer sized white pigment particles usually made of titanium dioxide. This are covered with a layer of dye being in contact with an electrolyte. When light hits the dye it is raised to excited state from where it injects electrons into the titanium dioxide. The electrons disperse in the nanoporous layer from where they are conducted outside the cell to the anode. The dye will get an electron back from the electrolyte, which gets its electron from the cathode, all together resulting in an electric flow. As a result light is converted into electrical energy.

Dye sensitized solar cells can be applied for a broad range of applications ranging from the lightweight low-power market to large-scale applications showing a wide flexibility in end product design. Their good energy conversion efficiency in diffuse light, room lamp or cloudy weather, the color variation by choosing dyes, the graphical design flexibility by using printing processes gives them a competitive edge over silicon in providing electric power for both indoor and outdoor standalone electronic equipment.

Currently, state-of-the-art dye-sensitized cells show energy conversion efficiencies around 11% on lab scale. Sony has achieved world-leading results in terms of energy conversion efficiency in the experimental module of dye-sensitized cells (energy conversion efficiency is 8.4 % having an active area of 17.11 cm2 (AIST, April 2009).

MSL contribution to this project is to improve and to develop new materials for DSSC. Currently, a new class of metal free sensitizer dyes is under development, the so called Squarylium dyes. The target is to design dyes that enable a broader absorption of the photons, in particular those of the long wavelength region. One unique new dye was developed and realized, 'Solar Green', which fulfills the request and also shows increased efficiency when applied together with other organic dyes in the solar cell.

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