Im Mittelpunkt der vorliegenden Dissertation stand die Herstellung von organischen Leuchtdioden und Passiv-Matrix-Displays an einer neuartigen Durchlauf-Depositionsanlage. Die Abscheidung von "small molecule" Materialien im Hochvakuum wurde dabei mittels organischer Molekularstrahldeposition (OMBD) durchgeführt. Um effiziente Leuchtdioden zu erzielen, sind die Bauelemente als Mehrschichtsystem aufgebracht worden. Als Grundstruktur kam eine Schichtenfolge zur Anwendung, die als Löchertransporter aus dem Starburst-Derivat 2-TNATA, daran anschließend einem tertiären Arylamin, dem elektronenblockierenden a-NPB sowie dem Oxinat-Komplex Alq3 besteht. Dabei diente das Aluminium-Oxinat als Elektronenleiter und Emissionsmaterial. Mit dem Quinacridon-Derivat QAD als Dotierstoff wurde außerdem eine OLED-Struktur mit Gast-Wirtsystem realisiert Eine kontrollierte und reproduzierbare Deposition der organischen Materialien ist eine unabdingbare Voraussetzung, um organische Leuchtdioden kommerziell als Mehrschichtbauelemente herstellen zu können. Dazu wurde ein Hochvakuumsystem der Firma Applied Films installiert und in Betrieb genommen. Die VES 400/13-Entwicklungsanlage ist als Vertical Evaporation and Sputtering Durchlaufsystem für bis zu 400 mm hohe Substrate mit 11 individuellen Prozesskammern sowie zwei daran anschließenden Stickstoffboxen konzipiert. Diese Technologie ermöglicht das Aufdampfen einer oder nacheinander mehrerer Schichten auf beliebiges Substratmaterial. Entsprechend den Erfordernissen sind wichtige Prozessparameter wie Depositionsrate, Transportgeschwindigkeit des Substrates sowie Filmdicke der funktionellen Schichten in einem weiten Bereich frei einstellbar. Neben einer ausgeglichenen Löcher- und Elektroneninjektion werden die Eigenschaften der hergestellten Leuchtdioden durch die Dicken der einzelnen Schichten, der Beweglichkeit der Ladungsträger in den verwendeten organischen Materialien sowie der energetischen Lage der höchsten besetzten und niedrigsten unbesetzten Molekülorbitale der Halbleiter bestimmt. Als undotierte OLED-Struktur wurde eine Schichtenfolge aus ITO / 2-TNATA / NPB / Alq3 / Mg verwendet. Die Stärke der elektrischen Kontakte betrug jeweils etwa 150 nm für ITO bzw. Magnesium. Die organischen Halbleiterfilme verfügten über Lagendicken von 60 / 10 / 60 nm. Eine derart aufgebaute Leuchtdiode zeigte ein grünes Emissionsspektrum, dessen Mittenwellenlänge bei etwa 537 nm lag und eine Halbwertsbreite von circa 112 nm aufwies. Für die Betriebsspannung, die Leuchtdichte, die Strom- sowie die Leistungseffizienz ergaben sich für die beiden Stromdichten von 3 mA/cm² und 30 mA/cm² optimierte Werte zu 5,3 V bzw. 9,4 V, 100 cd/m² bzw. 1317 cd/m², 3,3 cd/A bzw. 4,4 cd/A sowie 2 lm/W bzw. 1,5 lm/W. Das Sperr- oder Gleichrichtungsverhältnis Gv wurde für die beiden gemessenen Maximal-spannungen von ±10 Volt zu <5 x 107 bestimmt. Durch die Dotierung der Alq3-Emissionsschicht mit etwa 1 mol% des Quinacridon-Derivats QAD und Hinzufügen einer separaten Elektronentransportschicht konnte eine Steigerung der Elektrolumines-zenz erreicht werden. Der OLED-Aufbau des Gast-Wirt-Systems verfügt über einen Schichtenstapel mit den Lagen ITO / 2-TNATA / NPB / Alq3 + QAD / Alq3 / Mg. Die Filmdicken der organischen Schichten der OLED mit den besten Eigenschaften betragen 60 / 10 / 35 / 25 nm. Die anorganischen elektrischen Kontakte waren jeweils etwa 150 nm dick. Die dotierten Bauelemente zeigen ein bei einer Mittenwellenlänge von 527 nm emittierendes, grünes Spektrum. Mit einer geringen Halbwertsbreite von 28 nm ist die Bedingung einer schmalen Emissionsbreite für die Anwendung in OLED-Displays erfüllt. Die Betriebsspannung, die Leuchtdichte, die Strom- und die Leistungseffizienz ergeben für die beiden Stromdichten von 6,2 mA/cm² und 45,6 mA/cm² optimierte Werte zu 10,8 V bzw. 17,0 V, 445,4 cd/m² bzw. 3816,7 cd/m², 7,2 cd/A bzw. 8,4 cd/A sowie 2,1 lm/W bzw. 1,6 lm/W.

Im Mittelpunkt der vorliegenden Dissertation stand die Herstellung von organischen Leuchtdioden und Passiv-Matrix-Displays an einer neuartigen Durchlauf-Depositionsanlage. Die Abscheidung von "small molecule" Materialien im Hochvakuum wurde dabei mittels organischer Molekularstrahldeposition (OMBD) durchgeführt. Um effiziente Leuchtdioden zu erzielen, sind die Bauelemente als Mehrschichtsystem aufgebracht worden. Als Grundstruktur kam eine Schichtenfolge zur Anwendung, die als Löchertransporter aus dem Starburst-Derivat 2-TNATA, daran anschließend einem tertiären Arylamin, dem elektronenblockierenden a-NPB sowie dem Oxinat-Komplex Alq3 besteht. Dabei diente das Aluminium-Oxinat als Elektronenleiter und Emissionsmaterial. Mit dem Quinacridon-Derivat QAD als Dotierstoff wurde außerdem eine OLED-Struktur mit Gast-Wirtsystem realisiert Eine kontrollierte und reproduzierbare Deposition der organischen Materialien ist eine unabdingbare Voraussetzung, um organische Leuchtdioden kommerziell als Mehrschichtbauelemente herstellen zu können. Dazu wurde ein Hochvakuumsystem der Firma Applied Films installiert und in Betrieb genommen. Die VES 400/13-Entwicklungsanlage ist als Vertical Evaporation and Sputtering Durchlaufsystem für bis zu 400 mm hohe Substrate mit 11 individuellen Prozesskammern sowie zwei daran anschließenden Stickstoffboxen konzipiert. Diese Technologie ermöglicht das Aufdampfen einer oder nacheinander mehrerer Schichten auf beliebiges Substratmaterial. Entsprechend den Erfordernissen sind wichtige Prozessparameter wie Depositionsrate, Transportgeschwindigkeit des Substrates sowie Filmdicke der funktionellen Schichten in einem weiten Bereich frei einstellbar. Neben einer ausgeglichenen Löcher- und Elektroneninjektion werden die Eigenschaften der hergestellten Leuchtdioden durch die Dicken der einzelnen Schichten, der Beweglichkeit der Ladungsträger in den verwendeten organischen Materialien sowie der energetischen Lage der höchsten besetzten und niedrigsten unbesetzten Molekülorbitale der Halbleiter bestimmt. Als undotierte OLED-Struktur wurde eine Schichtenfolge aus ITO / 2-TNATA / NPB / Alq3 / Mg verwendet. Die Stärke der elektrischen Kontakte betrug jeweils etwa 150 nm für ITO bzw. Magnesium. Die organischen Halbleiterfilme verfügten über Lagendicken von 60 / 10 / 60 nm. Eine derart aufgebaute Leuchtdiode zeigte ein grünes Emissionsspektrum, dessen Mittenwellenlänge bei etwa 537 nm lag und eine Halbwertsbreite von circa 112 nm aufwies. Für die Betriebsspannung, die Leuchtdichte, die Strom- sowie die Leistungseffizienz ergaben sich für die beiden Stromdichten von 3 mA/cm² und 30 mA/cm² optimierte Werte zu 5,3 V bzw. 9,4 V, 100 cd/m² bzw. 1317 cd/m², 3,3 cd/A bzw. 4,4 cd/A sowie 2 lm/W bzw. 1,5 lm/W. Das Sperr- oder Gleichrichtungsverhältnis Gv wurde für die beiden gemessenen Maximal-spannungen von ±10 Volt zu <5 x 107 bestimmt. Durch die Dotierung der Alq3-Emissionsschicht mit etwa 1 mol% des Quinacridon-Derivats QAD und Hinzufügen einer separaten Elektronentransportschicht konnte eine Steigerung der Elektrolumines-zenz erreicht werden. Der OLED-Aufbau des Gast-Wirt-Systems verfügt über einen Schichtenstapel mit den Lagen ITO / 2-TNATA / NPB / Alq3 + QAD / Alq3 / Mg. Die Filmdicken der organischen Schichten der OLED mit den besten Eigenschaften betragen 60 / 10 / 35 / 25 nm. Die anorganischen elektrischen Kontakte waren jeweils etwa 150 nm dick. Die dotierten Bauelemente zeigen ein bei einer Mittenwellenlänge von 527 nm emittierendes, grünes Spektrum. Mit einer geringen Halbwertsbreite von 28 nm ist die Bedingung einer schmalen Emissionsbreite für die Anwendung in OLED-Displays erfüllt. Die Betriebsspannung, die Leuchtdichte, die Strom- und die Leistungseffizienz ergeben für die beiden Stromdichten von 6,2 mA/cm² und 45,6 mA/cm² optimierte Werte zu 10,8 V bzw. 17,0 V, 445,4 cd/m² bzw. 3816,7 cd/m², 7,2 cd/A bzw. 8,4 cd/A sowie 2,1 lm/W bzw. 1,6 lm/W.

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.

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.

By using phosphorescent and thermally activated delayed fluorescence emitters, the internal quantum efficiency of organic light-emitting diodes (OLEDs) can now reach 100%. However, a major fraction of generated photons is trapped inside the device, because of the intrinsic multi-layer device structure and the mismatch of refractive indices. This thesis comprises different approaches for the efficiency enhancement of planar OLEDs. In particular, outcoupling strategies to extract trapped photons to obtain highly efficient OLEDs are investigated.

Over the last decades organic light-emitting diodes (OLEDs) and organic solar cells (OSCs) have gained considerable attention as efficient, flexible, lightweight, and potentially low-cost technology for lighting and display applications or as a renewable energy source, respectively. However, achieving long-term stability remains challenging. Revealing and understanding aging processes is therefore of great interest. This work presents fundamental investigations to understand and circumvent organic device degradation. In the first part, single materials used in organic devices were investigated. By tailoring an attenuated total reflection infrared (ATR-IR) spectrometer to the specific needs and subsequent measurements, it is shown that the tris(8-hydroxyquinoline)aluminum (Alq3) molecule, a well known fluorescent green emitter, degrades during air exposure by the formation of carbonyl groups. By using a laser desorption/ionization time of flight mass spectrometer (LDI-TOF-MS) it was shown that a,w-bis-(dicyanovinylen)-sexithiophen (DCV6T-Bu4), a well known small-molecule material which is used as part of the active layer, reacts with oxygen during ultraviolet (UV) irradiation. By using climate boxes and a sun simulator the impact of dry and humid air as well as sunlight on C60, a widely-used acceptor molecule in organic solar cells, was investigated. The breaking of the C60 cage to C58 and C56 and the further reaction of these components with oxygen as well as the dimerization of C58 and C56 molecules were found. The degradation products such as C58O increase with air exposure time but they are independent of the humidity level of the ambient air as well as sunlight irradiation. Subsequent annealing leads to a decrease of the C58O concentration. Many efficient n-dopants are prone to degradation in air, due to the low ionization potentials, thereby limiting the processing conditions. It was found that the air exposure of the highly efficient n-dopant tetrakis(1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidinato)ditungsten(II) (W2(hpp)4) leads to oxidation reactions of the molecule to [W(hpp)2 + O] and other degradation products. The decay constant of W2(hpp)4 and the matching mean growth time of the [W(hpp)2 + O] degradation as well as a second very quick degradation of the dopant could be determined. The two decay constants can be explained by the assumption that W2(hpp)4 molecules, which are involved in the charge transfer, do degrade slower due to the fact that the charge transfer leads to a downshift of the energy levels of the W2(hpp)4 molecule. Apart from the properties of the organic materials, other effects such as the impact of different purification systems on the material purity as well as the dependence of material purity on the OLED lifetime has been investigated. No correlations between the purification grade and the amount of impurities were found. OLEDs which contain N,N\'-di(naphthalen-1-yl)-N,N\'-diphenyl-benzidine (alpha-NPD) purified in a vertically interlaced stainless steel sublimation systems shows slightly higher external quantum efficiencies compared to tube-based vacuum sublimation systems. The devices which contain alpha-NPD purified by a sublimation system have an extended lifetime. Finally, the impact of residual gases during device fabrication on OLED lifetime and electrical characteristics was investigated. It was found that water vapor introduces an additional series resistance to the OLED, while the other gases do not influence the electric characteristics. The presence of nitrogen or oxygen impacts the lifetime of the OLEDs by the same amount. Nitrogen is non-reactive, this leads to the conclusion that the influence of nitrogen and oxygen on the OLED lifetime is of non-chemical nature, such as changes in the morphology of the organic layers. Water vapor introduces an additional, even faster degradation process within the first hours of OLED operation. As major sources of device degradation, the dimerization of 4,7-diphenyl-1,10-phenanthroline (BPhen) as well as the complexation reaction of alpha-NPD with a bis(1-phenylisoquinoline)iridium(III) (Ir(piq)2) fragment was identified.

We demonstrate a new approach for fabricating alternating current driven organic electroluminescent devices using the concept of doping in organic semiconductors. Doped charge transport layers are used for generation of charge carriers within the device, hence eliminating the need for injecting charge carriers from external electrodes. The device is an organic-inorganic hybrid: We exploit the mechanical strength and chemical stability of inorganic semiconductors and combine it with better optical properties of organic materials whose emission color can be chemically tuned so that it covers the entire visible spectrum. The device consists of an organic electroluminescence (EL) layer composed of unipolar/ambipolar charge transport materials doped with organic dyes (10 wt% ) as well as molecularly doped charge generation layers enclosed between a pair of transparent insulating metal oxide layers. A transparent indium doped tin oxide (ITO) layer acts as bottom electrode for light outcoupling and Aluminium (Al) as top reflective electrode. The electrodes are for applying field across the device and to charge the device, instead of injection of charge carriers in case of direct current (DC) devices. Bright luminance of up to 5000 cd m-2 is observed when the device is driven with an alternating current (AC) bias. The luminance observed is attributed to charge carrier generation and recombination, leading to formation of excitons within the device, without injection of charge carriers through external electrodes.

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.