This work addresses two substantial problems of organic electronic devices: the controllability and adjustability of performance, and the integration using scalable, high resolution patterning techniques for planar thin-film transistors and novel vertical transistor devices. Both problems are of particular importance for the success of transparent and flexible organic electronics in the future. To begin with, the static behavior in molecular doped organic pin-diodes is investigated. This allows to deduce important diode parameters such as the depletion capacitance, the number of active dopant states, and the breakdown field. Applying this knowledge, organic pin-diodes are designed for ultra-high-frequency applications and a cut-off-frequency of up to 1GHz can be achieved using optimized parameters for device geometry, layer thickness, and dopant concentration. The second part of this work is devoted to organic thin-film transistors, high resolution patterning techniques, as well as novel vertical transistor concepts. In particular, fluorine based photo-lithography, a high resolution patterning technique compatible to organic semiconductors, is introduced fielding the integration of organic thin-film transistors under ambient conditions. However, as it will be shown, horizontal organic thin-film transistors are substantially limited in their performance by charge carrier injection. Hence, down-scaling is inappropriate to enlarge the transconductance of such transistors. To overcome this drawback, a novel vertical thin-film transistor concept with a vertical channel length of ∼50nm is realized using fluorine based photo-lithography. These vertical devices can surpass the performance of planar transistors and hence are prospective candidates for future integration in complex electronic circuits.

This work aims at improving the understanding of the fundamental physics behind molecular doping of organic semiconductors, being a requirement for efficient devices like organic light-emitting diodes (OLED) and organic photovoltaic cells (OPV). The underlying physics is studied by electrical conductivity and thermoelectrical Seebeck measurements and the influences of doping concentration and temperature are investigated. Thin doped layers are prepared in vacuum by thermal co-evaporation of host and dopant molecules and measured in-situ. The fullerene C60, known for its high electron mobility, is chosen as host for five different n-dopants. Two strongly ionizing air-sensitive molecules (Cr2(hpp)4 and W2(hpp)4) and three air-stable precursor compounds (AOB, DMBI-POH and o-MeO-DMBI-I) which form the active dopants upon deposition are studied to compare their doping mechanism. High conductivities are achieved, with a maximum of 10.9 S/cm. Investigating the sample degradation by air-exposure, a method for regeneration is proposed, which allows for device processing steps under ambient conditions, greatly enhancing device fabrication possibilities. Various material combinations for p-doping are compared to study the influence of the molecular energy levels of host (MeO-TPD and BF-DPB) and dopant (F6-TCNNQ and C60F36). Corrections for the only estimated literature values for the dopant levels are proposed. Furthermore, the model system of similar-sized host pentacene and dopant F4-TCNQ is studied and compared to theoretical predictions. Finally, a model is developed that allows for estimating charge carrier mobility, density of free charge carriers, doping efficiency, as well as the transport level position from combining conductivity and Seebeck data.:1 Introduction 2 Fundamentals of Organic Semiconductors 2.1 Conventional Semiconductors 2.2 Organic Semiconductors 2.3 Seebeck Effect 2.4 Correlation of Seebeck Coefficient and Charge Carrier Density 3 Experimental 3.1 Seebeck Setup 3.2 Materials 4 Air-Sensitive n-Dopants in C60 4.1 Conductivity 4.2 Thermoelectric Measurements 4.3 Morphology 4.4 Degradation 4.5 Conclusion 5 Air-Stable n-Dopants in C60 5.1 Conductivity 5.2 Thermoelectric Measurements 5.3 Morphology 5.4 Conclusion for AOB and DMBI-POH 5.5 o-MeO-DMBI-I 6 p-Dopants in Amorphous Hosts 6.1 Conductivity 6.2 Thermoelectric Measurements 6.3 Degradation 6.4 Conclusion 7 Pentacene p-Doped by F4-TCNQ 7.1 Conductivity Changes after Preparation 7.2 Relation of Conductivity to Doping Concentration 7.3 Comparison of Seebeck Energy and Activation Energy 7.4 Conclusion 8 Estimating the Doping Efficiency and the Mobility 8.1 Lower Limit of the Mobility 8.2 Lower Limit of the Doping Efficiency 8.3 Conclusions from Seebeck Measurements 8.4 Assuming a Constant Transport Level 8.5 Applying the Models to p-Doped Data 8.6 Conclusion 9 Summary and Outlook 9.1 Summary 9.2 Outlook / Diese Arbeit untersucht organische Halbleiter und den Einfluss von molekularer Dotierung auf deren elektrische Eigenschaften, mit dem Ziel effizientere Bauelemente wie organische Leuchtdioden oder Solarzellen zu ermöglichen. Mittels Leitfähigkeitsuntersuchungen sowie thermoelektrischen Seebeck-Messungen werden die Einflüsse der Dotierkonzentration sowie der Temperatur auf die elektrischen Eigenschaften dünner dotierter Schichten analysiert. Das Abscheiden der Schichten durch Koverdampfen im Vakuum ermöglicht eine in-situ Analyse. Das Fulleren C60, bekannt für besonders hohe Elektronenbeweglichkeit, wird als Wirt für fünf verschieden n-Dotanden, zwei extrem stark ionisierende luftreaktive (Cr2(hpp)4 und W2(hpp)4) sowie drei luftstabile (AOB, DMBI-POH und o-MeO-DMBI-I), verwendet. Dies ermöglicht Schlüsse auf die unterschiedlichen zugrunde liegenden Dotiermechanismen und das Erreichen von Leitfähigkeiten von bis zu 10.9 S/cm. Für einen der luftreaktiven Dotanden wird die Probendegradation an Luft untersucht und eine Regenerationsmethode aufgezeigt, die Prozessierungsschritte in Luft erlaubt und somit entscheidend für zukünftige Bauelementfertigung sein könnte. Verschiedene p-dotierte Materialkombinationen werden untersucht, um den Einfluss der molekularen Energieniveaus von Wirt (MeO-TPD und BF-DPB) und Dotand (F6-TCNNQ und C60F36) auf die Dotierung zu studieren. Dies ermöglicht Schlussfolgerungen auf die in der Literatur bisher nur abgeschätzten Energieniveaus dieser Dotanden. Ferner werden die Eigenschaften des bereits theoretisch modellierten Paares Pentacen und F4-TCNQ mit den Vorhersagen verglichen und die Abweichungen diskutiert. Abschießend wird ein Modell entwickelt, das die Abschätzung von Dotiereffizienz, Ladungsträgerkonzentration, Ladungsträgerbeweglichkeit sowie der Position des Transportniveaus aus Leitfähigkeits- und Seebeck-Messungen erlaubt.:1 Introduction 2 Fundamentals of Organic Semiconductors 2.1 Conventional Semiconductors 2.2 Organic Semiconductors 2.3 Seebeck Effect 2.4 Correlation of Seebeck Coefficient and Charge Carrier Density 3 Experimental 3.1 Seebeck Setup 3.2 Materials 4 Air-Sensitive n-Dopants in C60 4.1 Conductivity 4.2 Thermoelectric Measurements 4.3 Morphology 4.4 Degradation 4.5 Conclusion 5 Air-Stable n-Dopants in C60 5.1 Conductivity 5.2 Thermoelectric Measurements 5.3 Morphology 5.4 Conclusion for AOB and DMBI-POH 5.5 o-MeO-DMBI-I 6 p-Dopants in Amorphous Hosts 6.1 Conductivity 6.2 Thermoelectric Measurements 6.3 Degradation 6.4 Conclusion 7 Pentacene p-Doped by F4-TCNQ 7.1 Conductivity Changes after Preparation 7.2 Relation of Conductivity to Doping Concentration 7.3 Comparison of Seebeck Energy and Activation Energy 7.4 Conclusion 8 Estimating the Doping Efficiency and the Mobility 8.1 Lower Limit of the Mobility 8.2 Lower Limit of the Doping Efficiency 8.3 Conclusions from Seebeck Measurements 8.4 Assuming a Constant Transport Level 8.5 Applying the Models to p-Doped Data 8.6 Conclusion 9 Summary and Outlook 9.1 Summary 9.2 Outlook

Im Bereich der organischen Halbleiter wurden bedeutende Fortschritte erzielt, die die Materialwissenschaft und Elektronikentwicklung beeinflussen. Diese Materialien sind flexibel, leicht und kosteneffizient, was ihre Anwendung in Photovoltaik, Leuchtdioden und flexiblen elektronischen Geräten fördert. Verbesserte Herstellungstechniken und ein besseres Verständnis der physikalischen Eigenschaften haben diese Entwicklung unterstützt. Aktuelle Forschung vertieft das Verständnis der Grenzflächen, Ladungstransportmechanismen und Optimierungsmöglichkeiten durch molekulare Dotierung. Das erste Kapitel behandelt die grundlegenden Konzepte der elektronischen Eigenschaften organischer Materialien. Das zweite Kapitel beschreibt die untersuchten Materialien und Charakterisierungstechniken. Das Kapitel über Ergebnisse und Diskussion untersucht die elektronischen Eigenschaften von DN4T und isoDN4T, ihre Reorganisationsenergien und die Auswirkungen von Strukturphasen und Wechselwirkungen. Weitere Abschnitte behandeln die Phänomene an Grenzflächen und die molekulare Dotierung. Ziel dieser Arbeit ist es, Herausforderungen im Bereich organischer Halbleiter anzugehen und ihr Anwendungsspektrum zu erweitern. / The field of organic semiconductors has advanced significantly, transforming material science and electronic engineering. These materials, noted for their flexibility, light weight, and cost-effectiveness, are used in photovoltaics, light-emitting diodes, and flexible electronic devices. Progress is driven by improved fabrication techniques and a deeper understanding of their physical properties at the molecular level. Current research aims to enhance the understanding of interfaces, charge transport mechanisms, and optimization pathways through molecular doping. The first chapter introduces fundamental concepts of the electronic properties of organic materials. The second chapter covers studied materials and characterization techniques, including absorbance spectroscopy, Atomic Force Microscopy, Scanning Tunneling Microscopy, and Near-edge X-ray Absorption Fine Structure, focusing on Photoemission Spectroscopy. The results and discussion chapter explores DN4T and isoDN4T, highlighting their reorganization energies and interface phenomena. The thesis addresses challenges in organic semiconductors and aims to expand their applications.