Les matériaux conjugués ont fait l’objet de beaucoup de recherches durant les dernières années. Les nouveaux matériaux présentent des propriétés intéressantes que ce soit au niveau optique, électrique, mécanique ou même les trois en même temps. La synthèse reste la difficulté principale dans la fabrication de dispositifs électroniques. Les méthodes utilisées pour y parvenir sont l’électropolymérisation, le couplage de Suzuki ou de Wittig. Ces techniques comportent encore de nombreuses contraintes et s’avèrent difficilement réalisables à grande échelle. Les thiophènes, les pyrroles et les furanes ont démontré une bonne conductibilité et une bande de conduction basse due à une conjugaison accrue. L’objectif ici est de synthétiser des oligomères principalement composés de thiophènes dans le but d’en caractériser les propriétés spectroscopiques, électrochimiques et de conduction. La synthèse est souvent l’étape délicate de la fabrication de matériaux conjugués. Nous présentons ici une méthode de synthèse simple par modules avec des unités hétérocycliques. Les modules complémentaires sont attachés par condensation entre un aldéhyde et une amine menant à la formation d’un lien robuste, l’azomethine. Les résultats des propriétés photophysiques et électrochimiques de ces matériaux conjugués seront présentés. En ayant recours à différents groupes électrodonneurs et électroaccepteurs, en variant le degré de conjugaison ou en utilisant différents hétérocycles, les propriétés spectroscopiques, électrochimiques et de bande de conduction peuvent être adaptées à volonté, ce qui en fait des matériaux aux propriétés modelables. Ces nouvelles molécules seront analysées pour en déceler les propriétés recherchées dans la fabrication d’OLED. Nous explorerons les domaines de l’oxidation electrochimique réversible et de la polymérisation menant à la fabrication de quelques prototypes simples. / Conjugated materials have received much attention recently as they show promise for industrial applications. These materials are interesting because of the many new possibilities for devices combining unique optical, electrical and mechanical properties. The synthesis is the major difficulty in the fabrication of electronic devices. Usual methods to do so are electropolymerisation, Suzuki or Wittig coupling. Those techniques are full of constraints and are difficult to scale-up. Thiophenes, pyrroles and furans demonstrated good conductibility and low band-gap due to increased conjugation. Our main goal is to synthesize oligomers made principally of thiophene to characterize their spectroscopic, electrochemical and conduction properties. Synthesis is the most important step in the making of conjugated material. A synthetically simple and modular route to novel conjugated material consisting of heterocyclic units is presented. These complementary modules are linked by condensing aldehydes and amines leading to robust azomethine bonds. The resulting photophysical and electrochemical properties of these conjugated materials will be presented. Through the use of different electron donor and acceptor groups, degree of conjugation or by using different heterocycles, the spectroscopic, electrochemical and band-gap properties can be tailored leading to materials with tunable properties. Those new molecules will be analysed to detect properties suitable for OLED fabrication. This presentation will also address the electrochemical reversible oxidation and polymerization of these compounds leading to the making of simple devices.

Organic light-emitting diodes (OLEDs) have drawn much attention in the last two decades. In recent years, the power efficiency of OLEDs has been increased to exceed the efficiency of fluorescent light bulbs. However, such high-efficiency devices are typically based on small molecules that have to be evaporated in vacuum. A much higher fabrication throughput and therefore lowered costs are expected if high-efficiency OLEDs were processed from solution. This thesis shows how solution-processed electrophosphorescent multilayer OLEDs can be achieved by starting with an evaporated three-layer device structure and replacing layer by layer with a solution-processed layer. First, the hole-transport layer was replaced by a polymer and high efficiencies were observed when using a hole-transport polymer with a high ionization potential and a low hole mobility. Then, the emissive layer was replaced by a copolymer consisting of hole-transport groups and emissive complexes in its side-chains. OLEDs with four different colors are shown where the orange devices showed the highest efficiency. The orange copolymer was further optimized by making changes to the chemical nature of the polymer, such as different molecular weight, different concentrations of the emissive complex and different linkers between the side-chains and the polymer backbone. Finally, a three-layer solution-processed OLED was fabricated by crosslinking the hole-transport and the emissive layer, and by spin-coating an electron-transport polymer on top. Moreover, using the photocrosslinking properties of the emissive layer, solution-processed multilayer OLEDs of two different colors were patterned using photolithography to fabricate a white-light source with a tunable emission spectrum. Furthermore, with more and more organic semiconductors being integrated into the circuitry of commercial products, good electrical models are needed for a circuit design with predictive capabilities. Therefore, a model for the example of an organic single-layer diode is introduced in the last chapter of this thesis. The model has been implemented into SPICE and consists of an equivalent circuit that is mostly based on intrinsic material properties, which can be measured in independent experiments. The model has been tested on four different organic materials, and good agreement between model and experimental results is shown.

Ce travail porte sur l'amélioration des performances en vieillissement de micro-écrans vidéo à matrice active en technologie OLED sur Silicium. La perte d'efficacité lumineuse et la dérive en tension induites par le vieillissement des OLED restent depuis plusieurs années un point faible inhérent à cette technologie et représente toujours un verrou dans la commercialisation des micro-écrans sur un marché encore jeune. Nous proposons ici une étude d'optimisation d'un empilement OLED blanc bi-émetteurs à émission vers le haut basée sur l'amélioration systématique des modes de défaillances reconnus des OLED et adaptée aux spécificités de réalisation de micro-écrans à très forte résolution. Des outils originaux tels que des structures simplifiées de types monocouche ou monoporteur seront utilisés pour comprendre et réduire ces différents mécanismes de dégradation. Du fait de la complexité des structures OLED actuelles, des structures simplifiées seront notamment développées et analysées dans le but d'accéder à la compréhension des phénomènes intrinsèques de dégradation opérant au sein des couches organiques, à leurs interfaces ou encore aux interfaces avec les électrodes. Une méthode de caractérisation électrique encore peu utilisée dans le cas des LED organiques, la spectroscopie d'impédance, sera également développée. Cette technique de caractérisation électrique très prometteuse et surtout non destructive permet à travers l'étude des comportements capacitifs des dispositifs l'accès à de nombreuses informations relatives à la dynamique des charges liées ou mobiles dans les zones de bulk ou interfaciales des matériaux. / The present study deals with active-matrix OLED microdisplays, based on a white top-emitting bi-emitters structure. The optimization of these devices lifetime is the main point of this manuscript. The luminous efficiency loss and the voltage drift induced while ageing of the device under constant current driving conditions are indeed key parameters. A first part consists in understanding the main degradation mechanisms known to operate in OLED devices. A focus on intrinsic mechanisms is here chosen to improve devices lifetime. Extrinsic mechanisms like encapsulation issues or other process optimization are not developed in this work. We propose here a systematic study on the influence of OLED structure parameters on initial but especially on aging performances. The optimization of anode electrical contact through plasma treatments and a thin oxide interlayer show very interesting results for reducing operating bias and voltage drift induced while aging under constant current. The enhancement of doping percentage in doped injection layers also show significant improvement on devices performances, with the great advantage of being a useful tool for controlling devices efficiency. We also find that an optimization of the emission layers thicknesses could lead to great lifetime improvement. Those results are also combined and confirmed by a Design Of Experiments meant to determine the influence of the main process parameters on devices performances. Finally, we initiate the characterization of our OLED devices using impedance spectroscopy measurements. From the modeling of single-layer structures to the understanding of simple bipolar devices through analysis of capacitive evolution of full-stack devices with time, we here show that this technic appears very useful for the understanding of charge carrier dynamic and could help reducing charge accumulation.

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Orientadora: Profa. Dra. Karina Passalacqua Morelli Frin / Tese (doutorado) - Universidade Federal do ABC, Programa de Pós-Graduação em Ciência e Tecnologia/Química, Santo André, 2018. / Neste trabalho foram estudadas as propriedades fotofisicas e eletroquimicas dos compostos polipiridinicos fosforescentes de Re(I), fac-[ReCl(CO)3(N^N)] e fac-[Re(PPh3)(CO)3(N^N)]+, em que N^N = 1,10-fenantrolina (phen), 4,7-dimetil-1,10-fenantrolina (Me2phen) ou 4,7-dimetoxi-1,10-fenantrolina ((MeO)2phen) e PPh3 = trifenilfosfina e dos compostos fosforescentes ciclometalados de Ir(III), mer-[Ir(ppy)2(L^X)], em que L^X= 4,4fff'-(1,4-fenileno-bis-(2,2f,6f,2ff-terpiridina)) (tpy), carboxilato de 3-iodopiridinilmetila (Ipic) e ppy = 2-fenilpiridina. Ademais, o desempenho de dispositivos eletroluminescentes emissores de luz com esses compostos foi investigado por meio da capacidade de injecao e transporte de carga e transferencia de energia entre matriz e dopante. Os compostos foram sintetizados, purificados, caracterizados por meio de espectroscopias UV-visivel, na regiao do infravermelho, IV, e ressonancia magnetica nuclear de hidrogenio, 1H RMN. Os compostos de Re(I) e Ir(III) se encontram nas conformacoes facial e meridional, respectivamente.Nos espectros de absorcao dos compostos fac-[ReL(CO)3(N^N)], L = Cl e PPh3, e mer-[Ir(ppy)2(L^X)] foram observadas duas regioes: uma de mais alta energia, atribuida as transicoes intraligantes (IL) e, uma de menor energia, atribuida as transicoes de transferencia de carga do metal para o ligante (MLCT). Foi investigada a emissao desses compostos em solucao e em meio rigido, que pode ser atribuida ao estado excitado triplete de energia mais baixa. Para os compostos de Re(I), a temperatura ambiente, essa emissao pode ser atribuida principalmente ao estado excitado triplete de transferencia de carga do metal para o ligante polipiridinico (3MLCTRe¨N^N*) e que, em meio rigido, apresenta um maior carater do estado excitado triplete centrado no ligante (3IL), observando-se a inversao entre esses estados para os compostos com os ligantes polipiridinicos Me2phen e ((MeO)2phen. Para os compostos de Ir(III), a temperatura ambiente, a emissao pode ser atribuida ao estado excitado triplete de transferencia de carga do metal para o ligante auxiliar 3MLCTIr+ppy¨L^N, e que, em meio rigido, para o composto mer-[Ir(ppy)2(Ipic)], ocorre a inversao entre os estados 3MLCT e 3IL e, portanto, a emissao e atribuida a este ultimo estado excitado. Os tempos de vida obtidos para os compostos de Re(I), 0,18-2,52 ¿Ês, e de Ir(III), 60 ns - 0,43 ¿Ês, sao consistentes com estados emissores tripletes. Os rendimentos quanticos, constantes de decaimento radiativas e nao radiativas, potenciais de oxidacao e reducao tambem foram avaliados. Os calculos dos niveis de energia HOMO (highest occupied molecular orbital) e do LUMO (lowest unoccupied molecular orbital) foram realizados e comparados aos do polimero poli(vinil)carbazol (PVK). / In this work, both photophysical and electrochemical properties of phosphorescent polypyridyl Re(I) compounds, fac-[ReCl(CO)3(N^N)] and fac-[Re(PPh3)(CO)3(N^N)]+, N^N = 1,10-phenanthroline (phen), 4,7-dimethyl-1,10- phenanthroline (Me2phen) and 4,7-dimethoxi-1,10-phenanthroline ((MeO)2phen) and PPh3 = triphenylphosphine and phosphorescent cyclometalated Ir(III) complexes, mer-[Ir(ppy)2(L^X)], where L^X= 4¿,4¿¿¿¿-(1,4-Phenylene)bis(2,2¿:6¿,2¿¿-terpyridine) (tpy), 3-iodopyridine-2-carboxylate (Ipic) e ppy = 2-phenylpyridine, were investigated. Furthemore, the performance of electroluminescent devices by means of the charge injection ability was investigated as well as transport and energy transfer between the host and guest. These compounds were synthesized, purified and characterized by Uv-visible, infrared and proton nuclear magnetic resonance, 1H NMR, spectroscopies. Re(I) and Ir(III) compounds are in facial and meridional geometries, respectively. In the absorption spectra of the fac-[ReL(CO)3(N^N)], L = Cl and PPh3, and mer-[Ir(ppy)2(L^X)] are observed two bands: the higher energy one, assigned to intraligand transitions (IL), and the lower energy one, assigned to metal to ligand charge transfer (MLCT) transition. The emission of the compounds was investigated in fluid and rigid media, which could be ascribed to the low-lying triplet excited state. For the Re(I) compounds, at room temperature, the emission is characteristic of the triplet metal-to-ligand charge transfer (3MLCTRe¨N^N*) and, in rigid media, shows some degree of the triplet ligand-centered (3IL) emission, observing the inversion between these states for the compounds with the polypyridine ligands Me2phen and (MeO)2phen. For the Ir(III) compounds, at room temperature, the emission could be assigned to the triplet low-lying metal-to-ligand charge transfer 3MLCTIr+ppy¨L^N, and, in rigid media, for the mer-[Ir(ppy)2(Ipic)] compound occurs the inversion between the 3MLCT and 3IL excited states, therefore, the emission is ascribed from the latter excited state. The lifetime obtained for the the Re(I) compounds, 0.18-2.52 ¿Ês, and for the Ir(III) compounds, 60 ns - 0.43 ¿Ês, are consistent with triplet excited states. The emission quantum yields, radiative and non-radiative rates, oxidation and reduction potentials were also evaluated. The calculations of the HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) energy levels were performed and the values compared to the poly(vinyl)carbazol polymer (PVK).

In this dissertation, we study the optical property of 2D graded photonic super-crystals (GPSCs) for photon management. We focused primarily on manipulation and control of light by using the newly discovered GPSCs which present great opportunity for electromagnetic wave control in photonic devices. The GPSC has been used to explore the superior capability of improving the light extraction efficiency of OLEDs. The enhancement of extraction efficiency has been explained in term of destructive interference of surface plasmon resonance and out-coupling of surface plasmon through phase matching provided by GPSC and verified by e-field intensity distributions. A large light extraction efficiency up to 75% into glass substrate has been predicted through simulation. We also study the light trapping enhancement in GPSCs. Broadband, wide incident angle, and polarization independent light trapping enhancement is achieved in silicon solar cells patterned with the GPSCs. In addition, novel 2D GPSCs were fabricated using holographic lithography through the interference lithography by two sets of multiple beams arranged in a cone geometry using a spatial light modulator (SLM). Finally, we also report a fabrication of GPSCs with a super-cell size of 12a×12a by using e-beam lithography. Diffraction pattern from GPSCs reveals unique diffraction properties. In an application aspect, light emitting diode arrays can be replaced by a single light emitting diode shinning onto the diffraction pattern for a uniform fluorescence.

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.

There is a huge demand for low-cost and compact laser devices in particular for point-of-care diagnostic, sensing, or optical communication. Organic solid-state lasers (OSLs) have a great potential to fill that gap due to their specific properties such as high optical gain, low lasing threshold, and spectral tunability. To miniaturize OSLs for micro-optical circuits two aspects are required: The spectrum of the laser should be easily tunable, and the pumping energy should be provided in a simple and compact method, in the best case electrically. In this work, we developed a simple, compact, easy to manufacture, and electrically tunable laser resonator using electroactive polymers. The cavity is formed between a highly reflecting distributed Bragg reflector (DBR) and a highly reflecting silver layer sandwiching a soft elastomer layer. A transparent electrode made by indium tin oxide is placed on the glass substrate below the DBR. If an external voltage between the transparent bottom electrode and the metal layer is applied, the elastomer layer is compressed by the electrostatic pressure, which leads to a blue shift of the optical modes of the microcavity. If an active material with a broad emission spectrum, such as organic molecules, is included inside the cavity layer, it enables the development of an electrically tunable OSL. Hence, we demonstrate a cost-effective approach towards an electrically tunable organic laser source particularly suitable for easily processable lab-on-chip devices. In the second part, a novel organic light emitting diode (OLED) architecture is realized enabling high current densities with low optical losses in the prospect of the realization of an electrically driven OSL. For this purpose, an additional highly conductive lateral transport layer (LTL) is introduced to achieve expansion of the charge recombination to the electrode-free area. Simulations by equivalent circuit approach allow for an analysis of the lateral distribution of the vertical current density to predict the lateral current density distribution in the high excitation regime (current densities ≈ 1 kA/cm² ). Moreover, the Joule heating of the device is reduced by restructuring the OLED layer stack. Thus, high current densities close to the predicted lasing threshold of 1 kA/cm² could be achieved. The results of the thesis presenting a significant step towards the development of an electrical pumped OSL.:1 Introduction 2 Theoretical Background 2.1 Optical Cavities 2.1.1 Fabry-Perot Resonator 2.1.2 Transfer Matrix Algorithm 2.1.3 Distributed Bragg Reflector 2.1.4 Optical Microcavities 2.1.5 Tunable Optical Cavities 2.2 Organic Semiconductors 2.2.1 Properties 2.2.2 Electronic Structure 2.2.3 Absorption and Emission Spectra 2.2.4 Electrical Current 2.2.5 Doping 2.3 Organic Light Emitting Diodes 2.3.1 Basic OLED 2.3.2 Pin-OLED 2.3.3 OLEDs at High Excitation 2.4 Organic Lasers 2.4.1 Fundamentals of a Laser 2.4.2 Organic Molecules as Active Medium 2.4.3 Electrical Pumping of Organic Lasers 2.5 Dielectric Elastomer Actuators 2.5.1 Principle of Operation 2.5.2 Silicone-Based Materials 2.5.3 Compliant Electrodes 3 Experimental Methods 3.1 Sample Fabrication 3.1.1 Dielectric Elastomer Actuators 3.1.2 Organic Light Emitting Diodes 3.2 Characterization Techniques 3.2.1 Optical Characterization 3.2.2 Electrical Characterization 4 Tunable Optical Cavities with Dielectric Elastomer Actuators 4.1 Design of the Tunable Optical Microcavity 4.1.1 Tunable Cavity with Thin Metal Electrode . 4.1.2 Compliant Metal Electrodes on Dielectric Elastomer Films 4.1.3 Actuator Performance of Thick Metal Electrode 4.1.4 Electro-mechanical Characteristic 4.2 Tunable Emission of Optical Elastomer Cavities 4.2.1 Incorporation of Organic Laser Dyes in the Elastomer 4.2.2 Tunable Photoluminescence Spectra 4.2.3 Lasing in Elastomer Cavities 5 Novel Architecture for OLEDs at High Excitation 5.1 OLEDs at High Excitations Using Emission from Metal-free Area 5.1.1 Simulation of the Lateral Distribution of the Vertical Current Density 5.1.2 Investigation of the Lateral Emission 5.1.3 Organic Zener Junction 5.1.4 Simulation of High Excitation Behavior 5.2 Reduction of Self-heating for OLEDs at High Excitation 5.2.1 Crossbar-OLED at High Current Densities 5.2.2 Change in Layer Structure 5.3 Fully Transparent Metal-free OLEDs 5.3.1 Highly doped C 60 as a Transparent Electrode 5.3.2 Investigation of the External Quantum Efficiency 6 Conclusion and Outlook / Insbesondere durch die wachsende Nachfrage in Point-of-Care-Diagnostik, Sensorik oder optischer Kommunikationstechnologie wird eine große Anzahl von günstigen und kompakten Laserbauteilen benötigt. Aufgrund ihrer spezifischen Eigenschaften, wie hoher optische Verstärkung, niedriger Laserschwelle und spektrale Durchstimmbarkeit, sind organische Festkörperlaser geeignete Kandidaten, um diese Lücke zu schließen. Für die Anwendung als mikrooptische Systeme werden zwei wesentliche Komponenten benötigt: Die spektrale Durchstimmbarkeit sowie das Pumpen des Lasers sollten mit einem einfachen und kompakten Verfahren realisiert werden, im besten Fall durch Anlegen einer elektrischen Spannung. In der vorliegenden Arbeit wurde ein kompakter, elektrisch durchstimmbarer Laserresonator entwickelt, welcher mittels eines dielektrischen Elastomeraktuators in wenigen Prozessschritten realisiert werden kann. Der Resonator besteht aus zwei hochreflektierenden Spiegeln, einem dielektrischen Bragg-Spiegels und einem Metallspiegel, die eine Resonatorschicht aus einem weichen, verformbaren Elastomer umschließen. Für die elektrische Aktuation wird eine Spannung zwischen einer transparenten Bodenelektrode aus Indiumzinnoxid unterhalb des Bragg-Spiegel und der Metallschicht angelegt. Durch die elektrostatische Anziehung beider Elektroden wird die Elastomerschicht zusammengedrückt, wodurch die optischen Moden des Resonators eine Blauverschiebung der Wellenlänge erfahren. Durch die Integration einens Fluoreszenzfarbstoffes mit einem breiten Emissionsspektrum innerhalb der Resonatorschicht, wird die Umsetzung eines elektrisch durchstimmbaren, organischen Festkörperlasers ermöglicht. Im zweiten Teil der Arbeit wird ein neuartiges Design für organische Leuchtdioden (OLED) vorgestellt, um diese bei hohen Stromdichten zu betreiben und gleichzeitig die optischen Verluste, die beim Einbau in einen optischen Mikroresonator auftreten, zu minimieren. Hierfür wird eine zusätzliche hoch leitfähige, organische Schicht, die laterale Transportschicht, in den Schichtaufbau der OLED integriert. Aufgrund des verstärkten lateralen Ladungsträgertransports wird die Rekombinationszone bis außerhalb der Elektroden bedeckten Fläche ausgeweitet. Mithilfe einer Simulation, welche die organischen Schichten mittels eines Ersatzschaltbildes beschreibt, war es möglich, die laterale Verteilung der vertikalen Stromdichte zu bestimmen und damit Vorhersagen über die Stromdichtenverteilung bei hohen Anregungen (≈ 1 kA/cm² ) zu treffen. Darüber hinaus ermöglicht eine geänderte Schichtreihenfolge der OLED, die Joulesche Erwärmung des Bauteils zu reduzieren. Dadurch ist es möglich, hohe Stromdichten überhalb der vorherge sagten Laserschwelle von 1 kA/cm² zu erreichen. Diese Ergebnisse stellen eine wichtige Voraussetzung für die Entwicklung eines elektrisch gepumpten, organischen Festkörperlasers dar.:1 Introduction 2 Theoretical Background 2.1 Optical Cavities 2.1.1 Fabry-Perot Resonator 2.1.2 Transfer Matrix Algorithm 2.1.3 Distributed Bragg Reflector 2.1.4 Optical Microcavities 2.1.5 Tunable Optical Cavities 2.2 Organic Semiconductors 2.2.1 Properties 2.2.2 Electronic Structure 2.2.3 Absorption and Emission Spectra 2.2.4 Electrical Current 2.2.5 Doping 2.3 Organic Light Emitting Diodes 2.3.1 Basic OLED 2.3.2 Pin-OLED 2.3.3 OLEDs at High Excitation 2.4 Organic Lasers 2.4.1 Fundamentals of a Laser 2.4.2 Organic Molecules as Active Medium 2.4.3 Electrical Pumping of Organic Lasers 2.5 Dielectric Elastomer Actuators 2.5.1 Principle of Operation 2.5.2 Silicone-Based Materials 2.5.3 Compliant Electrodes 3 Experimental Methods 3.1 Sample Fabrication 3.1.1 Dielectric Elastomer Actuators 3.1.2 Organic Light Emitting Diodes 3.2 Characterization Techniques 3.2.1 Optical Characterization 3.2.2 Electrical Characterization 4 Tunable Optical Cavities with Dielectric Elastomer Actuators 4.1 Design of the Tunable Optical Microcavity 4.1.1 Tunable Cavity with Thin Metal Electrode . 4.1.2 Compliant Metal Electrodes on Dielectric Elastomer Films 4.1.3 Actuator Performance of Thick Metal Electrode 4.1.4 Electro-mechanical Characteristic 4.2 Tunable Emission of Optical Elastomer Cavities 4.2.1 Incorporation of Organic Laser Dyes in the Elastomer 4.2.2 Tunable Photoluminescence Spectra 4.2.3 Lasing in Elastomer Cavities 5 Novel Architecture for OLEDs at High Excitation 5.1 OLEDs at High Excitations Using Emission from Metal-free Area 5.1.1 Simulation of the Lateral Distribution of the Vertical Current Density 5.1.2 Investigation of the Lateral Emission 5.1.3 Organic Zener Junction 5.1.4 Simulation of High Excitation Behavior 5.2 Reduction of Self-heating for OLEDs at High Excitation 5.2.1 Crossbar-OLED at High Current Densities 5.2.2 Change in Layer Structure 5.3 Fully Transparent Metal-free OLEDs 5.3.1 Highly doped C 60 as a Transparent Electrode 5.3.2 Investigation of the External Quantum Efficiency 6 Conclusion and Outlook

This thesis focuses mainly on the techniques to achieve high-performance top-emitting OLEDs, regarding device efficiency and lifetime for both non-inverted and inverted structures. It is thus organized as follows: In Chapter 2, the basic physics of organic semiconductor materials are reviewed, including the electronic properties of organic semiconductor materials, molecular excitations and their electronic transitions etc., which are believed to be critical for understanding of the work. Then, the general device physics of OLEDs are reviewed in detail, which includes almost every important electrical and optical process involved in the device. Finally, techniques and methods used to improve the device performance are summarized, which includes electrical doping of charge carrier transport layers. In Chapter 3, all organic materials, experimental techniques, and characterization methods used in this study are briefly described. In the following Chapter 4, techniques that are used for device optimization of non-inverted top-emitting OLEDs are discussed. Also, the mechanism of light outcoupling enhancement by a capping layer is discussed there. In the last part of Chapter 4, the influence of the optical device structure on the intrinsic quantum yield of the emitters is studied. Chapter 5 is focused on inverted top-emitting OLEDs, which are believed to be better applicable with current mainstream n-type amorphous silicon thin film transistor (TFT) technology. In this Chapter, the organic/metal and metal/organic interfaces are investigated in detail and their influence on device performance is discussed. In Chapter 6, the degradation of top-emitting OLEDs is studied, with a focus on the influence of electrode material and electrode thickness on the lifetime of top-emitting devices.

This work demonstrates an approach to develop low-cost, semi-transparent, long-term stable, and efficient organic photovoltaic (OPV) cells and organic light-emitting diodes (OLEDs) using various alternative electrodes such as conductive polymers, doped ZnO, and carbon nanotubes. Such electrodes are regarded as good candidates to replace the conventional indium tin oxide (ITO) electrode, which is expensive, brittle, and limiting the manufacturing of low-cost, flexible organic devices. First, we report long-term stable, efficient ITO-free OPV cells and transparent OLEDs based on poly(3,4-ethylene-dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) electrodes by using a solvent post-treatment or a structure optimization. In addition, a high performance internal light out-coupling system for white OLEDs based on PEDOT:PSS-coated metal oxide nanostructures is developed. Next, we demonstrate highly efficient ITO-free OPV cells and OLEDs with optimized ZnO electrodes doped with alternative non-metallic elements. The organic devices based on the optimized ZnO electrodes show significantly improved efficiencies compared to devices with standard ITO. Finally, we report semi-transparent OPV cells with free-standing carbon nanotube sheets as transparent top electrodes. The resulting OPV cells exhibit very low leakage currents with good long-term stability. In addition, the combination of various kinds of bottom and top electrodes for semi-transparent and ITO-free OPV cells is investigated. These results demonstrate that alternative electrodes-based OPV cells and OLEDs have a promising future for practical applications in efficient, low-cost, flexible and semi-transparent device manufacturing. / Die vorliegende Arbeit demonstriert einen Ansatz zur Verwirklichung von kostengünstigen, semi-transparenten, langzeitstabilen und effizienten Organischen Photovoltaik Zellen (OPV) und Organischen Leuchtdioden (OLEDs) durch die Nutzung innovativer Elektrodensysteme. Dazu werden leitfähige Polymere, dotiertes ZnO und Kohlenstoff-Nanoröhrchen eingesetzt. Diese alternativen Elektrodensysteme sind vielversprechende Kandidaten, um das konventionell genutzte Indium-Zinn-Oxid (ITO), welches aufgrund seines hohen Preises und spröden Materialverhaltens einen stark begrenz Faktor bei der Herstellung von kostengünstigen, flexiblen, organischen Bauelementen darstellt, zu ersetzten. Zunächst werden langzeitstabile, effiziente, ITO-freie Solarzellen und transparente OLEDs auf der Basis von Poly(3,4-ethylene-dioxythiophene):Poly(styrenesulfonate) (PEDOT:PSS) Elektroden beschrieben, welche mit Hilfe einer Lösungsmittel-Nachprozessierung und einer Optimierung der Bauelementstruktur hergestellt wurden. Zusätzlich wurde ein leistungsfähiges, internes Lichtauskopplungs-System für weiße OLEDs, basierend auf PEDOT:PSS-beschichteten Metalloxid-Nanostrukturen, entwickelt. Weiterhin werden hoch effiziente, ITO-freie OPV Zellen und OLEDs vorgestellt, bei denen mit verschiedenen nicht-metallischen Elementen dotierte ZnO Elektroden zur Anwendung kamen. Die optimierten ZnO Elektroden bieten im Vergleich zu unserem Laborstandard ITO eine signifikant verbesserte Effizienz. Abschließend werden semi-transparente OPV Zellen mit freistehenden Kohlenstoff-Nanoröhrchen als transparente Top-Elektrode vorgestellt. Die daraus resultierenden Zellen zeigen sehr niedrige Leckströme und eine zufriedenstellende Stabilität. In diesem Zusammenhang wurde auch verschiedene Kombinationen von Elektrodenmaterialen als Top- und Bottom-Elektrode für semi-transparente, ITO-freie OPV Zellen untersucht. Zusammengefasst bestätigen die Resultate, dass OPV und OLEDs basierend auf alternativen Elektroden vielversprechende Eigenschaften für die praktische Anwendung in der Herstellung von effizienten, kostengünstigen, flexiblen und semi-transparenten Bauelement besitzen.