In the first wave of commercialization of organic electronics, about ten years ago, active-matrix organic light-emitting diode (AMOLED) displays became the first large-scale industrial application of organic electronic devices. The victory continues and AMOLED displays attain an ever-increasing market share in the global display industry. In the second wave, organic solar cells are about to enter the mass-production stage, and the possibility for low-cost production on flexible substrates will revolutionize the solar in-dustry. The third wave will be the implementation of organic thin-film transistors for truly flexible, printed, large-area circuits. However, there is a multitude of challenges with regard to device physics, material, and process engineering which need to be overcome to make organic thin-film transistors fit for the step into industrial fabrication. The focus of this thesis is at organic thin-film transistors, covering the whole spectrum of device physics, design principles, and the exploration of new applications. In particular, charge carrier transport and injection in vertical organic transistors with ultra-short channel length are investigated in order to derive device architectures suitable for high and ultra-high frequency operation. Self-heating and a strongly thermally activated charge carrier transport at high current densities are identified as the limiting factors for high-frequency operation on low thermal conductivity, flexible substrates. Besides fundamental questions on charge carrier transport, this thesis also addresses questions related to the device fabrication. In particular, new fabrication methods for vertical organic transistors are proposed enabling reliable and stable device operation and integration of ultra-short channel length devices without using costly high-resolution patterning techniques. Beyond conventional organic thin-film transistors, this thesis explores possible paths for the fourth wave of organic electronics. In this context, mixed ionic-electronic conductors and organic electro-chemical transistors (OECTs) are identified as highly promising approaches for electronic bio-interfaces enabling ultra-sensitive detection of biological signals. Furthermore, these systems show fundamental properties of biological synapses, namely the synaptic plasticity, which renders the possibility to build brain-inspired, neuromorphic networks enabling highly efficient computing. In particular, the combination of OECTs acting as sensor units and self-learning neural networks at once enables the development of intelligent tags for medical applications. Overall, this thesis adds substantially new insight into the field of organic electronics and draws a vision towards further research and applications. The advancements in the field of vertical organic transistors open new perspectives for the implementation of organic transistors in high-resolution AMOLED displays or radio-frequency identification tags. Furthermore, the exploration of OECTs for neuromorphic computing will create a whole new research field across the disciplines of physics, material, and computer science.

Geschichtete bzw. 2D Materialien bieten interessante Eigenschaften für Halbleiteranwendungen, wie Photonik durch direkte Bandlücken und Miniaturisierung durch atomar dünne Schichten. Diese Arbeit behandelt die Isolierung von 2D-Materialien und die Kontrolle über ionische Modulation in den resultierenden Bauteilen. Im ersten Kapitel wird eine silbervermittelte Exfoliation für MoS₂ eingeführt, die Monolagen mit großer Fläche liefert. Diese Technik ist ebenso leistungsfähig wie goldvermittelte Prozesse und erfordert nur einen einfachen Heizschritt, was zukünftige Exfoliationen erleichtern könnte. Die folgenden Kapitel befassen sich mit Funktionen, die durch kontrolliertes ionisches Gating ermöglicht werden. Im zweiten Kapitel wird die kontrollierte Li-Interkalation in LixZrNCl genutzt, um Supraleitung bei niedriger Ladungsträgerdichte zu untersuchen (BCS-BEC-Übergang). Durch Steuerung der Li-Menge wurden Veränderungen in der Vortex-Dynamik aufgedeckt, z.B. ein Vorzeichenwechsel im Vortex-Hall-Effekt, was auf eine Veränderung der Vortex-Flussdynamik in BEC-ähnlicher Supraleitung zurückgeführt wurde. Diese Erkenntnisse sind relevant für die Entwicklung von Supraleitern. Das dritte Kapitel wechselt zu Bauteilen auf Basis der elektrochemischen Doppelschicht (EDL). Ein 2D MoS₂-synaptischer Transistor wurde demonstriert, wobei gezeigt wurde, dass die Hysterese auf Ionenretention an der EDL zurückzuführen ist. Diese Kombination eines 2D-Materials mit einem Polymerelektrolyten emuliert synaptische Lernprozesse wie gepaarte Puls-Fazilitation und arbeitet energieeffizient. Das letzte Kapitel verlagert das ionische Gating auf das Substrat mittels Li-Ionen-leitender Keramiken für operando-Messungen an 2D-Materialien. Zusammenfassend demonstriert diese Arbeit neben der Exfoliation die vielfältigen Funktionen, die durch kontrolliertes ionisches Gating verfügbar sind, einschließlich Supraleitung bei niedriger Ladungsträgerdichte, neuromorphe Bauteile und operando-Plattformen. / Layered materials and their 2D single-layer forms offer interesting properties for semiconductor applications, such as photonics due to direct band gaps and miniaturization through atomically thin layers. This work addresses the isolation of 2D materials and the control via ionic modulation in the resulting devices. In the first chapter, a silver-mediated exfoliation for MoS₂ is introduced, yielding large-area monolayers. This technique is as effective as gold-mediated processes and requires only a simple heating step, potentially simplifying future exfoliations. The following chapters explore functions enabled by controlled ionic gating. The second chapter utilizes controlled Li intercalation in LixZrNCl to investigate superconductivity at low charge carrier densities to investigate superconductivity within the BCS-BEC crossover. By adjusting the Li content, changes in vortex dynamics were revealed, such as a sign reversal in the vortex Hall effect, attributed to altered vortex flow in increasingly BEC-like superconductivity. These findings are relevant for the development of future superconductors. The third chapter shifts to devices based on the electric double layer (EDL). A 2D MoS₂ synaptic transistor was demonstrated, showing that hysteresis and hence the short-term memory effect stems from ion retention in the EDL formed at the 2D material electrolyte interface. This combination of a 2D material with a polymer electrolyte emulates synaptic learning processes like paired-pulse facilitation and operates in an energy-efficient manner. The final chapter translates the ionic gating to the substrate using Li-ion-conducting ceramics for operando measurements on 2D materials in “open-hood” devices. In summary, besides exfoliation, this work demonstrates the diverse functions achievable through controlled ionic gating applied to 2D and layered materials, including superconductivity at low charge carrier densities, neuromorphic devices, and operando platforms.