The tandem solar cell concept is a promising approach to improve the efficiency of photovoltaic devices. However, characterization of tandem solar cell devices is challenging since correct efficiency determination demands special experimental infrastructure as well as suitable characterization procedures. Even though the appropriate IEC and ASTM measurement standards define all that very precisely, they cannot be applied without special care to organic photovoltaics (OPV) because they were originally developed for inorganic devices. As a consequence, nowadays almost all tandem organic solar cell publications are not using correct characterization procedures, often resulting in questionable efficiency values. The aim of this work is developing a measurement procedure for tandem organic solar cells assuring their correct characterization. Therefore, at first the existing standards and measurement procedures for tandem solar cells are reviewed and challenges when applying these standards to organic solar cells are identified. As main challenges the relatively low fill factors and distinct nonlinearities of organic solar cells are identified. As preliminary experiments, single junction organic solar cells are investigated to analyze the influence of measurement parameters like bias irradiance, bias voltage, and chopper frequency on the external quantum efficiency (EQE) of organic solar cells. This results in parameter sets assuring minimized artifacts for the subsequent EQE determination of the subcells of tandem organic solar cells. The main part of this thesis presents the detailed characterization of a tandem OPV example device. First, EQE is measured and validated by two independent institutes. The EQE results are used to calculate the illumination conditions to reach AM1.5g conditions for both subcells with a multi-source sun simulator. The resulting efficiency value under standard reporting conditions (SRC) is found to be 5% lower than the efficiency measured with a single-source sun simulator. A full spectrometric characterization shows that differing fill factors of the subcells are the reason for this behavior. To overcome the main reason for the complicated measurement procedure of tandem solar cells, the inaccessibility of the individual subcells, three different approaches for the jV-characteristics determination of the subcells are presented. The so-called Bias Voltage Approach is based on EQE-measurements under varying bias voltage and needs no additional electrical contacts. Therefore, it can be applied to existing devices. The Voltage Contact Approach as well as the Current Contact Approach require in changed stack designs. Therefore, they cannot be applied to existing devices but give more accurate results. Finally, a procedure for characterizing tandem organic solar cells is formulated. This procedures aims at giving practical advice how to characterize tandem organic solar cells to achieve results conforming to the measurement standards and being as accurate and reproducible as possible. Hence, this thesis attempts to establish standards for a correct measurement of tandem organic solar cells of which other emerging solar cell technologies can profit as well.

Over the last three decades, the performance of OLEDs has been improved rapidly, however, as an important assessment for OLED, the EQE data are still quite low. As outlined in the theoretical background, the EQE is the product of out-coupling efficiency and internal quantum efficiency (IQE). Therefore, this thesis focuses on designing two types of polymers with different optical functionalities, to increase the EQE addressing the two aforementioned determining factors. Thus, the first part of the thesis addresses the light out-coupling efficiency in OLED devices. Here high refractive index (HRI) polymers are aimed for as potential material for the out-coupling layer, which are so far scarily reported for application in OLED devices, due to existing limitations, such as limited transparency, extra fluorescence, tedious synthesis, poor thermal stability and low solubility. However, if suitable polymers are becoming easily available, they will offer the unique advantage, compared to low molar mass HRI compounds, of being able to using cost-effective solution based technology for large area film preparation. In addition, polymeric materials will allow to introducing fully new concepts for increasing the light-out-coupling efficiency, like patterning allowing micro-lens preparation, or the incorporation of light scattering particles into the out-coupling layer. The approach described in this thesis is based on a previous work where HRI polymers were prepared via metal-free thiol-yne “A2+B3” polyaddition reaction, which led in an easy one-pot synthesis to hyperbranched polyvinylsulfides of high solubility and already reasonable high RI. For further increasing RI, in this work B3 as well as finally A2 monomers with high naphthalene content were chosen which should, in addition to the positive effect of the sulfur-containing units, render polymers with even higher RI, and hopefully also of high solubility due to the branching. A challenging aspect of this work was to find reaction conditions which allow the preparation of high molar mass as well as highly soluble, highly aromatic polymers by that A2+B3 approach, even so very sterically demanding monomers are used. In addition, the material properties should be fine-tuned by careful selection of the monomer ratio. It was expected that these new, easily available HRI polymers will be of high potential in OLED application. Thus, the work in this part of the thesis comprises on the one hand monomer and polymer synthesis as well as detailed characterization of the structure and the solution and thermal properties of the new materials. But on the other hand, the elucidation of the thin film preparation and the quality and optical properties of the resulting polymer films are major objectives. Finally, evaluation of the performance of the polymer films in an OLED device compared to conventionally low molar mass our-coupling layers was aimed for, which could be realized with the help of partners from the Institute of Applied Photophysics at TU Dresden. For increasing the IQE in OLEDs, this thesis focuses on the development of a new type of polymeric thermally activated delayed fluorescence (TADF) material. TADF materials have the potential of theoretical 100% IQE and are considered as key materials for the next generation of OLEDs. So far, a significant amount of low molar mass TADF molecules has been developed, however, only a limited number of design rules are reported so far for polymers, even though polymers would offer, as already outlined above, significant advantages with regard to processing cost-effectively more efficient OLEDs for large area application. The new concept described in this thesis for TADF polymers is based on a new monomer which exhibits individual promising structural units for achieving TAFD properties but does not emit TADF itself due to its large ΔEST (the energy gap between singlet S1 and triple T1 state). However, it has to be expected that once the monomer is polymerized, the resulting polymeric product will have reduced ΔEST due to the increased conjugation length and thus can be expected to emit TADF. This new concept has the potential to significantly increase the scope of polymeric materials with TADF properties. Thus the second part on the thesis focuses on the design of a new monomer based on carbazole units with a pendant benzophenone moiety and its polymerization and full structural elucidation with the help of model compounds involving intensive NMR and MALDI-TOF analysis. In addition to the expect TADF properties, the benzophenone unit will also provide the possibility for film stabilization and even photopatterning due to photo-crosslinking. Thus the study of film formation and photo-crosslinking of the new TADF polymers was a further objective of this thesis. Finally, first theoretical as well as experimental studies of the photo physical properties of the monomer, a low molar mass model compound and the polymer, again together with the partners from the Institute of Applied Photophysics, should provide evidence on the suitability of the new polymer design principle.

Organic solar cells are one of the most promising candidates for future solar power generation. They are thin and lightweight with several additional advantages such as scalability, environmental sustainability and low cost for processing and installation. However, the low charge carrier mobility of the absorbing material for organic solar cells requires thin absorber layers, limiting photon harvesting and the overall power conversion efficiency. Several attempts, e.g., periodically patterned structures and scattering layers have been tried to enhance the absorption of thin-film solar cells as light trapping elements. However, much effort is required to introduce light trapping structures to conventional rigid metal oxide electrodes and glass substrate. For instance, almost 13 hours are required to fabricate micro structures of 1 m2 area on glass, in contrast, 1 minute on PET using a same laser set-up and an additional scattering layers are demanded for providing light trapping effects to solar cells. In the last years, flexibility is emerging as the one of the major advantages of organic solar cells. To realize flexibility of solar cells, the classically used glass substrates and ITO electrodes are too brittle. Therefore, polymer materials are promising candidates to replace them as flexible electrodes and substrates. In this thesis, the highly transparent conducting polymer, PEDOT:PSS and PET equipped with an AlOx encapsulation layer are used as electrode and substrate, respectively. Besides the flexibility, additional light trapping elements, e.g. scattering particles, nano- and microstructures can be easily applied to the polymer materials since they have the potential for easier shaping and processing. In this study, we apply different light trapping and in-coupling approaches to organic solar cells. First, PET substrates are structured with a direct laser interference patterning system, which is a powerful and scalable one-step technique for patterning polymers. Almost 80 % of the light is diffracted by these patterned PET substrates and thereby the light path in the absorption layer is increased. Optical display films, commercially developed to be used as back light units of liquid crystal displays are also examined as light trapping substrates and exhibit similar enhancement as patterned PET. Moreover, since PEDOT:PSS is prepared by a solution-based process, TiO2 nanoparticles are added as light scattering elements to the PEDOT:PSS electrodes. Consequently, those electrodes provide a dual function as electrical contact and light trapping element. Finally, 2- or 3-dimensional nanostructures are printed by a nano-imprinting technique onto the surface of PEDOT:PSS with PDMS stamps. By controlling the temperature and the time of PEDOT:PSS during an annealing step, nanostructures are transferred from PDMS masks to PEDOT:PSS. To evaluate the effects of light trapping for all above mentioned approaches, flexible organic solar cells are produced by vacuum evaporation using blends of DCV5T-Me and C60 as absorber layer. The substrates are optically characterized using UV-vis spectrometer and goniometer measurements. The topography of the samples is measured by atomic force microscopy, scanning microscopy and optical microscopy. Bending tests with various radii are performed to test the flexibility of the substrates. In summary, light trapping effects are successfully implemented in the electrodes and substrates for OPVs, giving efficiency improvements of up to 16 %. The light trapping mechanisms in our approaches are extensively discussed in this thesis. / Organische Photovoltaik ist einer der vielversprechendsten Kandidaten für die zukünftige Solarstromgewinnung auf flexiblen Substraten. Um diese Flexibilität zu ermöglichen, sind herkömliche Glassubstrate mit ITO-Elektroden zu spröde. Ein vielversprechender Kandidat, um sowohl flexible Elektroden als auch flexible Substrate herzustellen, sind Polymere, da diese sehr biegsam und leicht zu verarbeiten sind. Deshalb wird in dieser Arbeit das hoch transparente, leitfähige Polymer PEDOT:PSS als Elektrode und PET (mit einer AlOx Verkapselungsschicht) als Substrat untersucht. Aufgrund der guten Prozessierbarkeit der Polymere konnten wir zusätzlich zu den eigentlichen Funktionen des Substrates und der Elektrode noch den Mechanismus des Lichteinfangs hinzufügen. Zusätzlich zu ihrer Flexibilität haben organische Solarzellen noch weitere Vorteile: sie sind dünn, leicht, skalierbar und verursachen vergleichsweise geringe Kosten für Herstellung und Installation. Ein Nachteil organischer Solarzellen ist die vergleichsweise geringe Ladungsträgerbeweglichkeit der Absorbermaterialien, welche oft die Schichtdicke der Absorbermaterialien begrenzt. Dies hat weniger absorbierte Photonen, weniger Stromdichte und somit einen geringeren Wirkungsgrad zur Folge. In den letzten Jahren wurden periodisch strukturierte Substrate und streuende Schichten als Lichteinfangelemente eingesetzt, um den Wirkungsgrad organischer Solarzellen mit dünnen Absorberschichten zu erhöhen. Gestaltungsregeln für solche Lichteinfangelemente sind noch weitestgehend unbekannt. Im Rahmen dieser Arbeit strukturieren wir PET Substrate mit einem direkten Laserinterferenzsystem, welches ein leistungsfähiges, skalierbares Einschrittverfahren zur Polymerstrukturierung ist. Da PEDOT:PSS aus der Lösung prozessiert wird, können wir weiterhin Nanopartikel hinzufügen, die der Elektrode zusätzlich noch lichtstreuende Eigenschaften geben. Außerdem können 2- bzw. 3-dimensionale Nanostrukturen leicht mithilfe einer Stempeltechnik eingeprägt werden. Um die Effekte des Lichteinfangs, welcher durch die oben genannten Methoden erzeugt wird, zu untersuchen, werden flexible organische Solarzellen mittels Vakuumverdampfung prozessiert. DCV5T-Me und C60 bilden dabei die photoaktive Schicht. Somit werden die Licht fangenden Eigenschaften dieser flexiblen Solarzellen ausgenutzt und ausführlich in der Arbeit diskutiert.

Die hier vorgelegte Arbeit beschäftigt sich mit der Aufklärung von Wasserstoffsorptionsphänomenen an Kohlenstoffmodifikationen, welche in der Literatur kontrovers diskutiert werden. Ziel war, die publizierten Ergebnisse nachzuvollziehen, die Phänomene zu erklären und Struktur-Eigenschafts-Beziehungen herzustellen. Dabei wurde zum Einen die Sorption von Wasserstoff an Graphit-Nano-Fasern und zum Andern die Sorption von Wasserstoff an alkalisalzdotiertem Graphit untersucht. Es konnte mit der vorliegenden Arbeit zweifelsfrei nachgewiesen werden, dass die zunächst publizierten Ergebnisse zur Wasserstoffspeicherung in Graphit-Nano-Fasern in keiner Weise realisierbar sind. Es wurde jedoch im Rahmen dieser Arbeit eine ungewöhnliche Sorptionscharakteristik der Graphit-Nano-Fasern gefunden. Des weiteren wurde im Rahmen dieser Arbeit festgestellt, dass die von Chen et. al. publizierten Ergebnisse zur Wasserstoffspeicherung an Lithium dotiertem Graphit zum großen Teil auf eine Reaktion mit Feuchtigkeit zurückzuführen sind. Jedoch konnte weiterhin eine deutliche Massenzunahme mit gereinigtem Wasserstoff nachgewiesen werden. Es ist anzunehmen, dass dieses Verhalten mit den insitu gefundenen neuen Phasen der Proben zusammen hängt.

Organic solar cell (OSC) has been an active research field over the past decades, due to their intrinsic advantages, such as low consumption of materials and energy, the applicability on flexible substrates and the degradability of the organic components. Compared with the solution processing technology using polymers as electron donor materials, small molecule vacuum deposition is regarded as a promising fabrication method, avoiding the use of toxic aromatic solvents and guaranteeing constant batch-to-batch performance. Moreover, it is much easier to realize multi-junction tandem solar cells (TSCs) by thermal deposition, and the leading power conversion efficiency (PCE) of 13.2% was achieved using three different absorbers by vacuum deposition (“Heliatek sets new organic photovoltaic world record efficiency of 13.2%” 2016). In this dissertation, novel electron donor materials are synthesized based on the molecular skeleton of a famous chromophore, boron dipyrromethene (BODIPY), and chemical modifications are carried out to tune the intense absorption bands of these dyes to near infrared (NIR, λ>750,nm) region. Efficient small molecule NIR absorbers are highly required for TSCs, because they can construct a complementary absorption over the visible and NIR spectral region in cooperation with a wide bandgap material. Three β-fused aza-BODIPY molecules with heterocyclic substituents on α-positions are prepared using organolithium reagents and phthalonitrile as the starting materials. The organolithium reagents, namely N-methylpyrrole, N-methylindole and 2-trimethylsilylthiophene, are used instead of commonly used Grignard reagents. Moreover, three corresponding aza-BODIPY derivatives are obtained by replacing one fluorine atom in the BF_{2} moiety by a cyano group. UV-vis absorption spectra reveal that all these materials are strong NIR absorbers, and their abortion in solid state cover a wide range from 600 to 1000,nm. OSCs with these aza-BODIPY donors give a best PCE of 3.0%, which is a reasonable value for the NIR devices with the maximum and the onset of the EQE spectrum around 850 and 950,nm respectively. A series of furan-fused BODIPYs with a electron withdrawing CF_{3} group on the meso-C are synthesized, and the photophysical/electrochemical properties can be tuned easily by the electronic properties of the substituents on the peripheral aromatic rings. The most promising candidate gives a high PCE of 6.1% in a single junction OSC with a J_{sc} of 13.3,mA/cm^{2}, a V_{oc} of 0.73,V, and a FF of 62.7%. A serial connected TSC is fabricated using this BODIPY as the low bandgap donor and a “green” donor, and its EQE spectrum covers a wide range from 400 to 900,nm. The PCE reaches 9.9% with a J_{sc} of 9.9,mA/cm^{2}, a V_{oc} of 1.70,V, and a FF of 59.0%. Based on the general structure of furan-fused BODIPY, alkyl or fluorinated alkyl substituents with larger volume is introduced on either peripheral aromatic rings or the meso-C. The variations that caused by these substituents on the photophysical and electrochemical properties are negligible. The investigations on the OSCs demonstrate that the introduction of these alkyl chain substituents have positive influence on the PCE values, which benefit mainly from the increased photocurrent. However, there is no positive relationship between the device performance and the volume of the alkyl chain substituents. BODIPY molecules have been demonstrated as efficient and promising NIR electron donor materials for vacuum-deposited OSCs. Taking advantages of facile molecular modification, oustanding photophysical behaviors and tunable electrochemical properties, this series of dyes are also intereting for other semiconductor devices.

The aim of this work was to investigate silver nanowire as well as carbon nanotube networks as transparent conducting electrodes for small molecule organic solar cells. In the framework of the nanowire investigations, a low-temperature method at less than 80 °C is developed to obtain highly conductive networks directly after the deposition and without post-processing. In detail, specific non-conductive organic materials act as a matrix where the nanowires are embedded in such that a mutual attraction based on capillary forces and hydrophobic interaction is created. This process is mediated by the ethanol contained in the nanowire dispersion and works only for sublayer materials which exhibit hydrophobic and hydrophilic groups at the same time. In contrast to high-temperature processed reference electrodes (210 °C for 90 min) without matrix, a slightly lower sheet resistance of 10.8 Ohm/sq at a transparency of 80.4 % (including substrate) is obtained by using polyvinylpyrrolidone as the sublayer material. In comparison to annealed silver nanowire networks, the novel approach yields a performance enhancement in corresponding organic solar cells which can compete with ITO-based devices. Furthermore, a novel approach for scalable, highly conductive, and transparent silver nanowire top-electrodes for organic optoelectronic devices is introduced. By utilizing a perfluorinated methacrylate as stabilizer, silver nanowires with high aspect ratio can be transferred into inert solvents which do not dissolve most organic compounds making this modified dispersion compatible with small molecule and polymer-based organic optoelectronic devices. The inert silver nanowire dispersion yields highly performing top-electrodes with a sheet resistance of 10.0 Ohm/sq at 80.0 % transparency (including substrate) directly after low-temperature deposition at 30 °C and without further post-processing. In comparison to similarly prepared reference devices comprising a thin-metal film as transparent top-electrode, reasonable power conversion efficiencies are demonstrated by spray-coating this dispersion directly on simple, air-exposed small molecule-based organic solar cells. Moreover, a deeper understanding of the percolation behavior of silver nanowire networks has been achieved. Herein, direct measurements of the basic network parameters, including the wire-to-wire junction resistance and the resistance of a single nanowire of pristine and annealed networks have been carried out for the first time. By putting the values into a simulation routine, a good accordance between measurement and simulation is achieved. Thus, an examination of the electrical limit of the nanowire system used in this work can be realized by extrapolating the junction resistance down to zero. The annealed silver nanowires are fairly close to the limit with a theoretical enhancement range of only 20 % (common absolute sheet resistance of approximately 10 Ohm/sq) such that a significant performance improvement is only expected by an enlargement of the nanowire length or by the implementation of new network geometries. In addition, carbon nanotube networks are investigated as alternative network-type, transparent bottom-electrode for organic small molecule solar cells. For that purpose, cleaning and structuring as well as planarization procedures are developed and optimized which maintain the optoelectronic performance of the carbon nanotube electrodes. Furthermore, a hybrid electrode consisting of silver nanowires covered with carbon nanotubes is fabricated yielding organic solar cells with only 0.47 % power conversion efficiency. In contrast, optimized electrodes comprising only carbon nanotubes show significantly higher efficiency. In comparison to identically prepared ITO devices, comparable or lower power conversion efficiencies of 3.96 % (in p-i-n stack), 4.83 % (in cascade cell) as well as 4.81 % (in p-n-i-p architecture) are demonstrated. For an inverted n-i-p stack design, the highest power conversion efficiency of 5.42 % is achieved.

Inorganic alternating current electroluminescent devices (AC-ELs) are known for their ruggedness and extreme long-term reliability, which is why they can often been found in industrial and medical equipment as well as in applications in the military sector. In contrast to the inorganic phosphors used in AC-ELs, organic materials offer a number of advantages, in particular a significantly higher efficiency, easier processibility, and a wide selection of emitter materials spanning the entire visible spectrum. Several efforts towards alternating current driven organic light-emitting devices have recently been made, however, important operating mechanism are still not well understood. In the first part of this theses, alternating current driven, capacitively coupled, pin-based organic light-emitting devices are investigated with respect to the influence of the thickness of the insulating layer and the intrinsic organic layer on the driving voltage. A three-capacitor model is employed to predict the basic behavior of the devices and good agreement with the experimental values is found. The proposed charge regeneration mechanism based on Zener tunneling is studied in terms of field strength across the intrinsic organic layers. A remarkable consistency between the measured field strength at the onset point of light emission (3–3.1 MV/cm) and the theoretically predicted breakdown field strength of around 3 MV/cm is obtained. The latter value represents the field required for Zener tunneling in wide band gap organic materials according to Fowler-Nordheim theory. In a second step, asymmetric driving of capacitively coupled OLEDs is investigated. It is found that different voltages and/or pulse lengths for positive and negative half-cycle lead to significant improvements in terms of brightness and device efficiency. Part two of this work demonstrates a device concept for highly efficient organic light-emitting devices whose emission color can be easily adjusted from, e.g., deep-blue through cold-white and warm-white to saturated yellow. The presented approach exploits the different polarities of the positive and negative half-cycles of an alternating current driving signal to independently address a fluorescent blue emission unit and a phosphorescent yellow emission unit vertically stacked on top of each other. The electrode design is optimized for simple fabrication and driving and allows for two-terminal operation by a single source. The presented approach for color-tunable OLEDs is versatile in terms of emitter combinations and meets application requirements by providing a high device efficiency of 36.2 lm/W, a color rendering index of 82 at application relevant brightness levels of 1000 cd/m², and warm-white emission color coordinates. The final part demonstrates an approach for full-color OLED pixels that are fabricated by vertical stacking of a red-, green-, and blue-emitting unit. Each unit can be addressed separately which allows to efficiently generate every color that is a superposition of spectra of the individual emission units. The device is built in a top-emission geometrywhich is highly desirable for display fabrication as the pixel can be directly deposited onto the back-plane electronics. Furthermore, the presented device design requires only three independently addressable electrodes which simplifies fabrication and electrical driving. The electrical performance of each individual unit is on par with standard pin single emission unit OLEDs, showing very low leakage currents and achieving high brightness levels at moderate voltages of around 3–4 V.

Elektrochemische Doppelschichtkondensatoren (engl. Electrochemical Double-Layer Capacitors, EDLCs) stellen eine zunehmend wichtige Technologie auf dem Markt der elektrischen Energiespeicher dar. Sie zeichnen sich durch die Aufnahmefähigkeit großer Energiemengen, eine hohe Langzeitstabilität und ein schnelles Ansprechverhalten aus. Diese Eigenschaften sind Gründe, weshalb EDLCs als Speicherbausteine für Energierück-gewinnungssysteme oder zur Stabilisierung der Stromversorgung in diversen elektronischen Bauelementen eingesetzt werden. Die Aufnahme der Energie erfolgt über Ladungsseparation von Elektrolytionen an der Elektrodenoberfläche. Die Kapazität der Speicherfähigkeit wird dabei maßgeblich vom Betrag der Elektrodenoberfläche und dem Abstand der Elektrolytionen zur Oberfläche der Elektrode bestimmt (bei gleichbleibendem Elektrolyten). In der gegenwärtigen Forschung werden neue Elektrodenmaterialien entwickelt, um über deren Systemeigenschaften, wie Leitfähigkeit und Porosität, die Leistungsfähigkeit der Doppelschichtkondensatoren weiter zu optimieren. Gängige Komponenten für Elektroden in diesen Bauelementen stellen Kohlenstoffmaterialien dar, da diese chemisch inert und zumeist kostengünstig in der Produktion sind. In der vorliegenden Arbeit sollte die Eignung der Materialklasse der Siliziumoxykarbid-abgeleiteten Kohlenstoffe (engl. Silicon Oxycarbide-Derived Carbons, SiOCDCs) für die Anwendung in elektrochemischen Doppelschichtkondensatoren untersucht werden. Die SiOCDCs wurden über die Pyrolyse (700 – 1500 °C) und Chlorierung (700 – 1000 °C) eines kohlenstoffreichen Polysilsesquioxans mit der theoretischen Zusammensetzung C6H5SiO3/2 erzeugt. Dabei zeigte sich, dass sowohl die porösen Eigenschaften als auch die Leitfähigkeit innerhalb der erhaltenen Kohlenstoffmaterialien stark von der Synthesetemperatur abhängen. Somit konnten reine Kohlenstoffe mit spezifischen Oberflächen bis zu 2400 m2 g-1 und Porenvolumina von 1,9 cm3 g-1 synthetisiert werden. Im Verlauf der Arbeit wurde eine geeignete Methode zur Verarbeitung der erzeugten Oxykarbid-abgeleiteten Kohlenstoffe zu Elektroden evaluiert, um eine elektrochemische Charakterisierung vorzunehmen. Ein vielversprechender Ansatz stellt die vollkommen trockene Umsetzung der SiOCDCs zu freistehenden Elektrodenschichten dar. Dieses Verfahren nutzt die Verreibung der Aktivkomponente mit einem geringen Anteil (5 Gew.-%) eines Bindemittels (Polytetrafluorethylen, PTFE) aus, um flexible und selbsttragende Elektrodenfolien zu erzeugen. Die Vorteile dieses Prozesses gegenüber anderen Verarbeitungsarten liegen darin, dass aufwendige Trocknungsverfahren während der Elektrodenherstellung entfallen und die Schichtdicken der resultierenden Folien unmittelbar eingestellt werden können. Während der Untersuchung der unterschiedlichen Elektrodensysteme im organischen Elektrolyten (1 M Tetraethylammoniumtetrafluoroborat-Lösung in Acetonitril) konnten spezifische Kapazitäten von bis zu 120 F g-1 gemessen werden. Des Weiteren zeigte sich der Einfluss der Kohlenstoffstruktur innerhalb der Aktivmaterialien auf die elektrochemischen Resultate. So konnte festgestellt werden, dass eine zunehmende Graphitisierung im Kohlenstoff, welche mit einer steigenden Mesoporosität im SiOCDC einherging, zu einer verbesserten Leitfähigkeit innerhalb der EDLC-Elektroden führte, aber auch eine Verringerung der spezifischen Kapazität bedeutete. Die Verringerung der Widerstände im System weitete erheblich den Bereich der nutzbaren Arbeitsfrequenzen und die Strombelastbarkeit des Elektrodenmaterials aus. So bestand die Möglichkeit ein mesoporöses Kohlenstoffmaterial zu synthetisieren, welches mit einer maximalen Arbeitsfrequenz von 8 Hz einen Wert zeigte, der zwei Größenordnungen über der Arbeitsfrequenz eines kommerziell erhältlichen Standards (Aktivkohle YP-50F) lag. Dieses exzellente Ansprechverhalten bildet die Grundlage für den Einsatz in Hochleistungsspeichersystemen. Des Weiteren offenbarte sich, dass die trocken prozessierten Elektroden das Potential für eine hohe Langzeitstabilität besitzen, da je nach Elektrodensystem ein Erhalt von 94% der Ursprungskapazität über 10.000 Lade-/Entladezyklen beobachtet werden konnte. Die Modifikation der Elektrodenmaterialien mittels CO2-Aktivierung und eine damit verbundene Erhöhung der spezifischen Oberfläche führten zu einer Verbesserung der spezifischen Kapazität der Aktivkomponenten um bis zu 33%. Zusammenfassend bleibt zu erwähnen, dass poröse Oxykarbid-abgeleitete Kohlenstoffe erfolgreich über die Chlorierung von keramischen Vorläuferverbindungen synthetisiert werden konnten. Die Kohlenstoffmaterialien zeigten nach der Prozessierung zu freistehenden und flexiblen Elektrodenfilmen vielversprechende Eigenschaften bei der Nutzung in elektrochemischen Doppelschichtkondensatoren, wie hohe spezifische Kapazitäten, gute Langzeitstabilitäten und hohe Arbeitsfrequenzen bei Lade- und Entladevorgängen.

Organische, lichtemittierende Dioden (OLEDs) bezeichnen neuartige Lichtquellen, welche zur Beleuchtung oder für Displayanwendungen nutzbar sind. Im Allgemeinen ist die Lichtausbeute durch den hohen Brechungsindex und die Dünnschichtgeometrie der OLED begrenzt. Der hohe Brechungsindex sorgt dafür, dass ein signifikanter Anteil des emittierten Lichts in der OLED durch Totalreflexion (TIR) gefangen ist. Durch den Dünnschichtaufbau der OLED wird außerdem die Lichterzeugung für resonante Moden der kohärenten optischen Mikrokavität erhöht. Dies gilt im Besonderen für die nichtstrahlenden Moden. In dieser Arbeit wurden zwei Methoden untersucht, um die Lichtausbeute aus OLEDs zu erhöhen. Zuerst wurde die Implementierung von Materialien mit niedrigem Brechungsindex angrenzend zum undurchsichtigen metallischen Rückkontakt untersucht. Die Modifizierung des Brechungindexes verändert die Dispersionsrelation der an der Grenzfläche zwischen Metall und Dielektrikum angeregten nicht-strahlenden Oberflächenplasmonpolariton-Resonanz (SPP). Dadurch wird der Phasenraum verkleinert, in welchen effizient Strahlung abgegeben werden kann. Da die SPP-Resonanz eine nichtstrahlende Verlustquelle der Mikrokavität darstellt, wird so die Auskopplungseffizienz der OLED erhöht. In experimentellen Umsetzungen konnte die externe Quanteneffizienz (EQE) sowohl für einen Emitter gesteigert werden, welcher eine isotrope Verteilung der Strahlungsquellen besitzt (Ir(ppy)3 , +19 %), als auch für eine vorzugsweise horizontale Ausrichtung (Ir(ppy)2 (acac), +18 %). Die Steigerung der EQE korrespondiert sehr gut mit der berechneten Steigerung der Auskopplungseffizienz für die jeweiligen Mikrokavitäten (+23 %, bzw. +19 %). Weitere optische Simulationen legen den Schluss nahe, dass dieser Ansatz ebenso für perfekt horizontale Ausrichtung der Quellen sowie für weiße OLEDs anwendbar ist. Als zweiter Ansatz wurde die erhöhte Lichtausbeute durch Bragg-Streuung an periodische Linienstrukturen untersucht. In dieser Arbeit wurden Methoden untersucht, bei denen die Oberflächen strukturiert wurde, auf welche die organischen Halbleiterschichten der OLEDs aufgebracht wurden. Für bottom-OLEDs (durch ein Substrat emittierende OLEDs), wurde direkt die transparente Elektrode durch ein Laserinterferenzablationsverfahren (DLIP) modifiziert. Zusätzlich wurden top-OLEDs untersucht (direkt aus der Mikrokavität Licht emittierende OLEDs), für welche alle Schichten auf eine periodisch strukturierte Photolackschicht aufgedampft wurden. Für die bottom-OLEDs konnte für eine Gitterkonstante von 0.71 μm eine Steigerung der EQE um 27 %, verglichen zu einer optimierten unstrukturierten Referenz, ermittelt werden. Eine Vergrößerung der Gitterkonstante führt zu einer Abnahme der EQE. Die erhöhte EQE wird auf die Überlagerung des planaren Emissionsspektrums mit Beiträgen von Bragg-gestreuten, ursprünglich nicht-strahlenden Moden zurückgeführt, wobei die Intensitäten der Anteile von der Gitterkonstante und der Strukturhöhe abhängen. Für die top-OLEDs konnte eine Steigerung der EQE um 13 % für eine Gitterkonstante von 1.0 μm festgestellt werden. Im Gegensatz zu den bottom-OLEDs wird für kleinere Gitterkonstanten (0.6 μm) hier die EQE nicht erhöht. Vielmehr kommt es durch die starke Veränderung des Emissionsspektrums zu einer Erhöhung der photometrischen Lichtausbeute um 13.5 %. Die starke Veränderung des Emissionspektrums wird auf eine kohärente Kopplung zwischen den Bragg-gestreuten Moden zurückgeführt, bedingt durch die starke optische Mikrokavität dieses OLED-Typs. Um diese Effekte quantitativ zu beschreiben, wurde ein entsprechendes Modell entwickelt und implementiert. Die Qualität der Simulationsergebnisse wird anhand von Literaturreferenzen überprüft, wobei eine gute Übereinstimmung zu experimentell gemessenen Spektren erzeugt wird. Mit dem Simulationsmodell werden Vorhersagen über das Emissionspektrum und die resultierenden Effizienzen möglich. Für bottom-OLEDs wurde festgestellt, dass eine starke Veränderung des Emissionspektrums für Gitterkonstanten unterhalb von 0.5 μm erzeugt werden kann. Hingegen sind für top-OLEDs sehr schwache Strukturen oder große Gitterkonstanten notwendig, um eine nur schwache Veränderung des Emissionsspektrums und damit einen allgemeinen Effizienzgewinn zu erzeugen. Bezüglich der Gitterkonstante, ist diese Erkenntnis ist im Gegensatz zur üblichen Herangehensweise zur Implementierung periodischer Streuschichten in OLEDs. Mit der implementierten Simulationsmethode werden jedoch Aussagen bzgl. Emissionspektrum und Effizienz für eine breite Spanne an OLED-Strukturen vor der experimentellen Umsetzung möglich. / Organic light-emitting diodes (OLEDs) are an attractive new light source for display and lighting applications. In general, the light extraction from OLEDs is limited due to the high refractive index of the active emitter material and the thin film geometry. The high refractive index causes the trapping of a significant portion of the emitted light due to total internal reflection (TIR). Due to the thin film layout, the light emission is enhanced for resonant modes of the coherent optical microcavity, in particular for light affected by TIR. In this work two approaches are investigated in detail in order to increase the light extraction efficiency of OLEDs. In a first approach, the implementation of a low refractive index material next to the opaque metallic back-reflector is discussed. This modifies the dispersion relation of the non-radiative surface plasmon polariton (SPP) mode at the metal / dielectric interface, causing a shift of the SPPs dispersion relation. Thereby, the phase space into which power can be efficiently dissipated by the emitter is reduced. For the SPP this power would have been lost to the cavity, such that in total the outcoupling efficiency is increased. In experiment, an increased external quantum efficiency (EQE) is observed for an emitter exhibiting isotropic orientation of the sources (Ir(ppy)3 ,+19 %), as well as for an emitter which shows preferential horizontal orientation (Ir(ppy)2 (acac), +18 %), compared to an optimized device which uses standard material. This corresponds very well to the enhancement of the outcoupling efficiencies of the corresponding microcavities (+23 %, resp. +19 %) reducing the refractive index of the hole transport layer by 15 %. Optical simulations indicate that the approach is generally applicable to a wide range of device architectures. These in particular include OLEDs with emitters showing a perfectly horizontal alignment of their transition dipole moments. Furthermore, the approach is suitable for white OLEDs. Bragg scattering was investigated as second option to increase the light extraction from OLEDs. The method requires a periodically structured surface. For the bottom-emitting OLEDs, this is achieved by a direct laser interference patterning (DLIP) of the transparent electrode. Additionally, top-emitting devices were fabricated onto periodically corrugated photoresist layers. Using a periodic line pattern with a lattice constant of 0.71 μm, the EQE of the bottom-emitting devices was enhanced by 27 % compared to an optimized planar reference. For the bottom-emitting layout, increasing the lattice constant leads to lower EQEs. The increased EQE is attributed to the superposition of the radiative cavity resonances by Bragg scattered intensities of trapped modes. The intensities depend on the lattice constants as well as the height of the periodic surface perturbation. For top-emitting OLEDs comprising a lattice constant of 1.0 μm the EQE was increased by 13 %. Reducing the lattice constant (0.6 μm) decreases the EQE, albeit the luminous efficacy is increased by 13.5 % due to a heavily perturbed emission spectrum. The perturbation is attributed to a coherent interaction of the Bragg scattered modes due to the strong optical microcavity for the top-emitting OLEDs. Thus, for strong perturbation specific emission patterns can be achieved, but an overall enhanced efficiency is difficult to obtain. To investigate the observed results theoretically, a detailed simulation approach is outlined. The simulation method is carefully evaluated using reference data from literature. Using the simulation approach, the emission patterns as well as the efficiencies of the devices can be estimated. The emission spectra reproduced from simulation are in good agreement with the experiment. Furthermore, for the bottom-emitting layout, a strong interaction can be found from simulations for lattice constants below 0.5 μm. For top-emitting OLEDs, the weak interaction regime seems to be more likely to result in an overall enhanced emission. This requires, in contrast to conventional opinion, very shallow perturbations or lattice constants which exceed the peak wavelength of the emission spectrum. However, with the established simulation approach a-priori propositions on the emission spectrum or particular beneficial device layouts become feasible.

Die Speicherung von Wasserstoff in Form von Hydriden im festen Aggregatzustand hat den Vorteil einer hohen volumetrischen und gravimetrischen Wasserstoffspeicherdichte, die sowohl für die stationäre als auch die mobile Anwendung nötig ist. Um die Anforderungen dieser Anwendungen erfüllen zu können, müssen die Speichereigenschaften dieser Materialien weiter verbessert werden. Als zentrales Konzept dieser Dissertation wird die Nanostrukturierung verfolgt, die eine vielversprechende Strategie zur Modifizierung der thermodynamischen und kinetischen Eigenschaften von Hydriden darstellt. Die Transmissionselektronenmikroskopie (TEM) stellt dabei eine unverzichtbare Untersuchungsmethode solch nanoskopischer Materialien dar. Als problematisch erweist sich dabei die durch Radiolyse hervorgerufene Zersetzung der meisten Hydride bei der Beleuchtung mit dem abbildenden Elektronenstrahl. Im ersten Teil dieser Arbeit wird eine Methodik entwickelt um dieses Phänomen quantitativ mit Hilfe von Valenzelektronenenergieverlustspektroskopie zu untersuchen. Hierzu kommt kugelgemahlenes MgH2 als Modellsystem zum Einsatz. Die Dehydrierung kann quantitativ durch die inelastische Streuung der hochenergetischen Elektronen am MgH2-Plasmon erklärt werden. Eine Lösung dieses grundlegenden Problems wird theoretisch an Hand von Multislice TEM-Kontrastsimulationen untersucht. Hierbei wird ein TEM Experiment unter Wasserstoff bei Umgebungsdruck anstatt unter Vakuum simuliert, was mit Hilfe eines speziellen TEM Halters, in dem das Gas durch elektronentransparente Fenster eingeschlossen ist, realisiert werden kann. Im zweiten Teil wird der Einfluss des Nanoconfinements (Nanoeinschließung), einer speziellen Form der Nanostrukturierung, des komplexen Hydrids LiBH4 auf dessen Wasserstoffspeichereigenschaften untersucht, wofür eine neuartige nanoporöse aerogel-ähnliche Kohlenstoff-Gerüststruktur zum Einsatz kommt. Diese wird durch Salt Templating synthetisiert - einer simplen und nachhaltigen Methode zur Herstellung nanoporöser kohlenstoffbasierter Materialien mit großen Porenvolumina. Es wird gezeigt, dass durch das Nanoconfinement die Wasserstoffdesorptionstemperatur, die für makroskopisches LiBH4 bei über 400 °C liegt, auf 310 °C sinkt und die Desorption bereits bei 200 °C einsetzt. Eine teilweise Rehydrierung ist unter moderaten Bedingungen (100 bar und 300 °C) möglich, wobei die Reversibilität durch eine partielle Oxidation des amorphen Bor gehemmt ist. Im Gegensatz zu Beobachtungen einer aktuellen Veröffentlichung von in hoch geordnetem, nanoporösen Kohlenstoff eingebetteten LiBH4 deuten die in-situ TEM-Heizexperimente der vorliegenden Arbeit darauf hin, dass beide Reaktionsprodukte (B und LiH) in den Poren des aerogel-ähnlichen Kohlenstoffs verbleiben. / Storing hydrogen in solid hydrides has the advantage of high volumetric and gravimetric hydrogen densities, which are needed for both stationary and mobile applications. However, the hydrogen storage properties of these materials must be further improved in order to meet the requirements of these applications. Nanostructuring, which represents one of the central approaches of this thesis, is a promising strategy to tailor the thermodynamic and kinetic properties of hydrides. Transmission electron microscopy (TEM) is an indispensable tool for the structural characterization of such nanosized materials, however, most hydrides degrade fast upon irradiation with the imaging electron beam due to radiolysis. In the first part of this work, a methodology is developed to quantitatively investigate this phenomenon using valence electron energy loss spectroscopy on ball milled MgH2 as a model system. The dehydrogenation can be quantitatively explained by the inelastic scattering of the incident high energy electrons by the MgH2 plasmon. A solution to this fundamental problem is theoretically studied by virtue of multislice TEM contrast simulations of a windowed environmental TEM experiment, which allows for performing the TEM analysis in hydrogen at ambient pressure rather than vacuum. In the second part, the effect of the nanoconfinement of the complex hydride LiBH4 on its hydrogen storage properties is investigated. For this, a novel nanoporous aerogel-like carbon scaffold is used, which is synthesized by salt templating - a facile and sustainable technique for the production of nanoporous carbon-based materials with large pore volumes. It is shown that the hydrogen desorption temperature, which is above 400 °C for bulk LiBH4, is reduced to 310 °C upon this nanoconfinement with an onset temperature as low as 200 °C. Partial rehydrogenation can be achieved under moderate conditions (100 bar and 300 °C), whereby the reversibility is hindered by the partial oxidation of amorphous boron. In contrast to recent reports on LiBH4 nanoconfined in highly ordered nanoporous carbon, in-situ heating in the TEM indicates that both decomposition products (B and LiH) remain within the pores of the aerogel-like carbon.