Organic Light-Emitting Diodes: Development of Electrode and Multilayer Deposition Processes

Organische Leuchtdioden weisen, verglichen mit anorganischen Leuchtdioden, viele Vorteile auf. So sind sie nicht nur energiesparender, sondern können auch in neuen flexiblen Technologien verwendet werden. Um ihr volles Potenzial auszuschöpfen, können zusätzliche Schichten und neue Materialien hinzugefügt werden. Der Ersatz spröder Elektroden durch dünne Metallschichten kann OLEDs flexibler machen, Zwischenschichten verbessern den Ladungstransport und neuartige Materialien können die Lösungsprozessierung von OLEDs vereinfachen. In den Kapiteln dieser Arbeit wurden je ein Ansatz zur Steigerung der Leistung von OLEDs untersucht. Es wurden dünne Silberschichten aus einer partikelfreien Silbertinte mittels Tintenstrahldruck hergestellt und ihre optischen sowie elektrischen charakterisiert. Die gedruckten Elektroden zeigen eine hohe Biegefestigkeit, bei gleichbleibend guten elektrischen Eigenschaften. Die damit hergestellten Leuchtdioden übertreffen in ihrer Effizienz Referenzdioden mit Indium Zinn Oxid Elektroden. Um die Effizienz organischer Leuchtdioden weiter steigern zu können wurden anschließend Zwischenschichten untersucht. Mittels einer gemischten Schicht aus Zinkoxid und einem Polymer konnte die Effizienz von invertierten Leuchtdioden signifikant gesteigert werden. Weiterhin wurden zwei neu synthetisierte Moleküle dazu verwendet, um die Benetzung von Perowskiten auf Elektroden zu verbessern und somit ihre Herstellbarkeit mittels Tintenstrahldruck zu ermöglichen. Abschließend wurde das Quervernetzen von Polymeren zur Herstellung von Mehrschichtsystemen erforscht. Hierbei wird ein die Löslichkeit eines Polymers durch verschiedene Ansätze verringert. Anhand des lichtemittierenden Polymers Super Yellow wurde dies demonstriert. Die Beständigkeit einer Schicht aus Super Yellow gegenüber Toluol konnte erfolgreich stark erhöht werden. Somit wurde eine nachfolgende Prozessierung einer zusätzlichen Schicht aus demselben Lösungsmittel ermöglicht.Organic light-emitting diodes have many advantages compared to their inorganic counterparts. Not only can they be used more energy-efficiently, but they can also be used in new, flexible technologies. To reach their full potential, additional layers and new materials can be added. Replacing brittle electrodes with thin metal layers can make OLEDs more flexible, intermediate layers improve charge transport, and novel materials can simplify solution processing of OLEDs. In each of the chapters of this thesis, an approach to increasing the performance of OLEDs was examined. Thin silver layers were produced from a particle-free silver ink using inkjet. Their optical and electrical properties were characterized. The printed electrodes show a high flexural strength while retaining good electrical properties. The efficacy of the light-emitting diodes produced in this way exceeds that of reference diodes. To be able to further increase the efficiency of organic light-emitting diodes, intermediate layers made of new material combinations were subsequently investigated. The efficiency of inverted light-emitting diodes could be significantly increased by means of a blend intermediate layer made of zinc oxide and a polymer. Furthermore, two newly synthesized molecules were used to improve the wetting of perovskites on electrodes and thus enable their manufacturability using inkjet printing. Finally, crosslinking of polymers to fabricate multilayer devices was investigated. Here, the solubility of a polymer is reduced by various approaches. This principle was demonstrated using the light-emitting polymer Super Yellow. The resistance of a layer of Super Yellow against toluene was successfully reduced significantly. Thus, subsequent processing of an additional layer from the same solvent was made possible

Glycosylation of hyperthermostable designer cellulosome components yields enhanced stability and cellulose hydrolysis

Biomass deconstruction remains integral for enabling second‐generation biofuel production at scale. However, several steps necessary to achieve significant solubilization of biomass, notably harsh pretreatment conditions, impose economic barriers to commercialization. By employing hyperthermostable cellulase machinery, biomass deconstruction can be made more efficient, leading to milder pretreatment conditions and ultimately lower production costs. The hyperthermophilic bacterium Caldicellulosiruptor bescii produces extremely active hyperthermostable cellulases, including the hyperactive multifunctional cellulase CbCel9A/Cel48A. Recombinant CbCel9A/Cel48A components have been previously produced in Escherichia coli and integrated into synthetic hyperthermophilic designer cellulosome complexes. Since then, glycosylation has been shown to be vital for the high activity and stability of CbCel9A/Cel48A. Here, we studied the impact of glycosylation on a hyperthermostable designer cellulosome system in which two of the cellulosomal components, the scaffoldin and the GH9 domain of CbCel9A/Cel48A, were glycosylated as a consequence of employing Ca. bescii as an expression host. Inclusion of the glycosylated components yielded an active cellulosome system that exhibited long‐term stability at 75 °C. The resulting glycosylated designer cellulosomes showed significantly greater synergistic activity compared to the enzymatic components alone, as well as higher thermostability than the analogous nonglycosylated designer cellulosomes. These results indicate that glycosylation can be used as an essential engineering tool to improve the properties of designer cellulosomes. Additionally, Ca. bescii was shown to be an attractive candidate for production of glycosylated designer cellulosome components, which may further promote the viability of this bacterium both as a cellulase expression host and as a potential consolidated bioprocessing platform organism

A guide to qualitative haze measurements demonstrated on inkjet-printed silver electrodes for flexible OLEDs

The search for alternative transparent electrodes to the commonly used indium tin oxide (ITO) in optoelectronic devices has led to solution-based approaches based on inkjet printing. As an additive manufacturing technique that allows drops to be positioned only where necessary, inkjet printing shows reduced waste of starting material compared to other methods such as spin coating. As a result, functional materials can be both coated and structured without the need for masks or lithographic pre-patterning of the substrate. For this contribution, we utilized a particle-free silver ink to produce a transparent electrode by inkjet printing. After printing, the silver ions were reduced to metallic silver by an argon plasma. The process takes place at low temperatures (ca. 40 – 50°C), making it suitable for use with flexible substrates, which are often temperature-sensitive. The printed silver layers show good electrical conductivity and optical transmittance, with a crystalline grain structure being formed and maintained during the metallization process. This structure forms a self-organized nanometer-size grid, whose structure allows light to pass through. Due to its nano-structured property, the haze of the electrode was investigated using a simple experimental setup based on a light source shining through the electrode and analyzing the size of the projected pattern. Such qualitative assessment can be a useful indication of the quality of the electrode and we provide details on how to replicate this setup. The final electrodes were implemented in solution-processed OLEDs, which showed bright luminance and overall low haze compared to ITO-based reference devices.Peer Reviewe

Glycosylation of hyperthermostable designer cellulosome components yields enhanced stability and cellulose hydrolysis

Biomass deconstruction remains integral for enabling second‐generation biofuel production at scale. However, several steps necessary to achieve significant solubilization of biomass, notably harsh pretreatment conditions, impose economic barriers to commercialization. By employing hyperthermostable cellulase machinery, biomass deconstruction can be made more efficient, leading to milder pretreatment conditions and ultimately lower production costs. The hyperthermophilic bacterium Caldicellulosiruptor bescii produces extremely active hyperthermostable cellulases, including the hyperactive multifunctional cellulase CbCel9A/Cel48A. Recombinant CbCel9A/Cel48A components have been previously produced in Escherichia coli and integrated into synthetic hyperthermophilic designer cellulosome complexes. Since then, glycosylation has been shown to be vital for the high activity and stability of CbCel9A/Cel48A. Here, we studied the impact of glycosylation on a hyperthermostable designer cellulosome system in which two of the cellulosomal components, the scaffoldin and the GH9 domain of CbCel9A/Cel48A, were glycosylated as a consequence of employing Ca. bescii as an expression host. Inclusion of the glycosylated components yielded an active cellulosome system that exhibited long‐term stability at 75 °C. The resulting glycosylated designer cellulosomes showed significantly greater synergistic activity compared to the enzymatic components alone, as well as higher thermostability than the analogous nonglycosylated designer cellulosomes. These results indicate that glycosylation can be used as an essential engineering tool to improve the properties of designer cellulosomes. Additionally, Ca. bescii was shown to be an attractive candidate for production of glycosylated designer cellulosome components, which may further promote the viability of this bacterium both as a cellulase expression host and as a potential consolidated bioprocessing platform organism

Septicemia Caused by Tick-borne Bacterial Pathogen Candidatus Neoehrlichia mikurensis

We have repeatedly detected Candidatus Neoehrlichia mikurensis, a bacterium first described in Rattus norvegicus rats and Ixodes ovatus ticks in Japan in 2004 in the blood of a 61-year-old man with signs of septicemia by 16S rRNA and groEL gene PCR. After 6 weeks of therapy with doxycycline and rifampin, the patient recovered

Glycosylation Is Vital for Industrial Performance of Hyperactive Cellulases

In the terrestrial biosphere, biomass deconstruction is conducted by microbes employing a variety of complementary strategies, many of which remain to be discovered. Moreover, the biofuels industry seeks more efficient (and less costly) cellulase formulations upon which to launch the nascent sustainable bioenergy economy. The glycan decoration of fungal cellulases has been shown to protect these enzymes from protease action and to enhance binding to cellulose. We show here that thermal tolerant bacterial cellulases are glycosylated as well, although the types and extents of decoration differ from their Eukaryotic counterparts. Our major findings are that glycosylation of CelA is uniform across its three linker peptides and composed of mainly galactose disaccharides (which is unique) and that this glycosylation dramatically impacts the hydrolysis of insoluble substrates, proteolytic and thermal stability, and substrate binding and changes the dynamics of the enzyme. This study suggests that the glycosylation of CelA is crucial for its exceptionally high cellulolytic activity on biomass and provides the robustness needed for this enzyme to function in harsh environments including industrial settings

Creation of a functional hyperthermostable designer cellulosome

Background: Renewable energy has become a field of high interest over the past decade, and production of biofuels from cellulosic substrates has a particularly high potential as an alternative source of energy. Industrial deconstruction of biomass, however, is an onerous, exothermic process, the cost of which could be decreased significantly by use of hyperthermophilic enzymes. An efficient way of breaking down cellulosic substrates can also be achieved by highly efficient enzymatic complexes called cellulosomes. The modular architecture of these multi-enzyme complexes results in substrate targeting and proximity-based synergy among the resident enzymes. However, cellulosomes have not been observed in hyperthermophilic bacteria. Results: Here, we report the design and function of a novel hyperthermostable “designer cellulosome” system, which is stable and active at 75 °C. Enzymes from Caldicellulosiruptor bescii, a highly cellulolytic hyperthermophilic anaerobic bacterium, were selected and successfully converted to the cellulosomal mode by grafting onto them divergent dockerin modules that can be inserted in a precise manner into a thermostable chimaeric scaffoldin by virtue of their matching cohesins. Three pairs of cohesins and dockerins, selected from thermophilic microbes, were examined for their stability at extreme temperatures and were determined stable at 75 °C for at least 72 h. The resultant hyperthermostable cellulosome complex exhibited the highest levels of enzymatic activity on microcrystalline cellulose at 75 °C, compared to those of previously reported designer cellulosome systems and the native cellulosome from Clostridium thermocellum. Conclusion: The functional hyperthermophilic platform fulfills the appropriate physico-chemical properties required for exothermic processes. This system can thus be adapted for other types of thermostable enzyme systems and could serve as a basis for a variety of cellulolytic and non-cellulolytic industrial objectives at high temperatures