<p dir="ltr">Conducting polymers have garnered enormous attention due to their unique properties, including tunable chemical structure, high flexibility, solution processability, and biocompatibility. They hold promising applications in flexible electronics, renewable energies, sensing, and healthcare. Despite notable progress in conducting polymers over the past few decades, most of them still suffer from complicated synthesis routes, limited processability, low electrical conductivity, and poor ambient stability compared to their inorganic counterparts. Additionally, the susceptibility of conducting polymers to high temperatures makes them not applicable in real-life electronics. To address the challenges of developing high-performance and stable conducting polymers, we present two key approaches: dopant innovation for polymer-dopant interaction engineering and the discovery of new conjugated polymer hosts. From the perspective of dopant design, we first utilize cross-linkable chlorosilanes (C-Si) to design thermally and chemically stable conductive polymer composites. C-Si can form robust siloxane networks and simultaneously<i> </i>dope the host conjugated polymers. Besides, we have introduced a new class of dopants, namely aromatic ionic dopants (AIDs). The use of AIDs allows for the separation of doping and charge compensation, two processes involved in molecular doping, and therefore leads to highly efficient doping and thermally stable doped systems. We then provide insights into the design of novel conjugated polymer hosts. Remarkably, we have developed the first thermodynamically stable n-type conducting polymer, n-doped Poly (3,7-dihydrobenzo[1,2-b:4,5-b′]difuran-2,6-dione) (n-PBDF). n-PBDF is synthesized from a simple and scalable route, involving oxidative polymerization and reductive doping in one pot in the air. The n-PBDF ink is solution processable with excellent ink stability and the n-PBDF thin film is highly conductive, transparent, patternable, and robust. In addition, precise control over the doping levels of n-PBDF has been achieved through chemical doping and dedoping. By tuning the n-PBDF thin films between highly doped and dedoped states, the system shows controllable conductivity, optical properties, and energetics, thereby offering potential applications in a variety of organic electronics. Overall, this research advances the fundamental understanding of molecular doping and offers insights for the development of high-conductivity, stable conducting polymers with tunable properties for next-generation electronics.</p>

Ziel dieser Arbeit war es, den grundlegenden Mechanismus des Ladungstransfers bei molekularer Dotierung an organisch-organischen Grenzflächen besser zu verstehen. Es wurde eine Vielfalt modernster spektroskopischer Methoden eingesetzt, um die elektronische Struktur und neue dotierungsinduzierte CT-Übergänge zu ergründen. Dazu gehören UPS und XPS für Valenzsignaturen und Kernniveauzustände. Absorptionsspektroskopie im UV-vis-NIR und Röntgenbereich wurde zur Bestimmung der Übergangsenergien eingesetzt. Schwingungsspektroskopie wurde eingesetzt, um den CT-Grad in DA-Systemen für gestapelte und gemischte Heteroübergänge zu quantifizieren. Strom-Spannungs-Messungen wurden zur Bestimmung der elektrischen Leitfähigkeit und Rasterkraftmikroskopie zur Charakterisierung der Oberflächenmorphologie eingesetzt. Die in dieser Arbeit behandelten Themen sind: (1) Planare Heteroübergänge aus DIP und F6TCNNQ wurden hergestellt. Sie wurden im Hinblick auf CT-Komplexbildung, Grenzflächendotierung und Exzitonenbindungsenergien an der D|A-Grenzfläche untersucht. (2) DBTTF wurde mit TCNNQ und F6TCNNQ in Lösung und in dünnen Filmen gemischt. Daraus wurde der Zusammenhang zwischen Dotierungsmechanismen, CTC- und IPA-Bildung, mit dem Aggregatzustand hergeleitet. (3.1) Rubren-Einkristalle wurden mit Mo(tfd)3 und CoCp2 p- und n-dotiert. Nach der Dotierung verschiebt sich die Banddispersion entsprechend, wohingegen die effektive Masse der Löcher konstant bleibt. (3.2) DBTTF-Einkristalle wurden mit TCNNQ, F6TCNNQ und Mo(tfd)3 dotiert. Aus den Änderungen der elektronischen Struktur wurden der CT über die D|A-Grenzfläche sowie die Dichte der Oberflächenzustände quantifiziert. (4) Von drei DA-Systemen mit unterschiedlicher GS-Wechselwirkungsstärke, DIP:C60, DIP:PDIR-CN2 und DIP|F6TCNNQ, wurden die Grenzflächenexzitonen charakterisiert. Ein Vergleich verschiedener Modelle, die die optische CTC Absorption aus dem DA-Energieniveauoffset beschreiben und abschätzen können, rundet die Ergebnisse ab. / The aim of this thesis was to enhance the understanding of the charge transfer mechanism during molecular doping at organic-organic interfaces. A wide range of state-of-the-art spectroscopic methods was employed to unravel the electronic structure and new CT transitions resulting from doping. This includes UPS and XPS for valence signatures and core level states. Absorption spectroscopies in the UV-vis-NIR and X-ray regions were used to determine transition energies. Vibrational spectroscopy was employed to quantify the CT degree in DA systems for stacked and mixed heterojunctions. Current-voltage measurements were used for the determination of electrical conductivities and scanning force microscopy for surface morphology characterization. The topics covered in this thesis are: (1) Planar heterojunctions of DIP and F6TCNNQ were fabricated. They were studied with regard to CT complex formation, interface doping and exciton binding energies at the D|A interface. (2) DBTTF was blended with TCNNQ and F6TCNNQ in solution and in thin films. From this, the connection of the two doping mechanisms, CTC and IPA formation, to the state of matter was derived. (3.1) Rubrene single crystals were p- and n-doped with Mo(tfd)3 and CoCp2. After doping, the band dispersion shifts accordingly, while the hole effective mass stays constant. (3.2) DBTTF single crystals were doped with TCNNQ, F6TCNNQ and Mo(tfd)3. From changes in the electronic structure, the CT across the D|A interface as well as the density of surface states were quantified. (4) From three DA systems with varying GS interaction strength, DIP:C60, DIP:PDIR–CN2 and DIP|F6TCNNQ, the interfacial excitons were characterized. A comparison of different models, which describe and allow to estimate the optical absorption in CTCs from the DA energy level offset, concludes the results.

Depuis une vingtaine d’années, le graphène est étudié à travers le monde pour ses propriétés opto-électroniques remarquables. Malgré tous ces efforts et la simplicité apparente de ce feuillet monoatomique de carbone, sa physique subtile continue de surprendre et reste à découvrir. Cette étude exploratoire vise à évaluer l’effet du dopage et de l’hydrogénation sur le spectre Raman du graphène afin de mieux comprendre les propriétés électroniques sous-jacentes. Pour ce faire, on utilise le RIMA, un imageur Raman hyperspectral qui se distingue des montages Raman traditionnels par sa capacité à produire rapidement des cartes Raman d’une centaine de microns de côté, ce qui permet de résoudre spatialement les propriétés de l’échantillon en plus d’avoir un nombre statistique de spectres. Les échantillons sont produits intégralement dans nos laboratoires et chaque procédé est contrôlé et détaillé dans ce mémoire. Le graphène est synthétisé par dépôt chimique en phase vapeur (Chemical Vapor Deposition, CVD) puis exposé à un faisceau d’hydrogène atomique à haute température pour former des liens C-H sur la surface. Le dopage est généré et contrôlé en immergeant simplement l’échantillon dans une solution de pH variable en ayant préalablement déposé des nanoparticules de platine à sa surface. L’équilibre chimique impliquant le couple rédox Pt/PtO permet de fixer son énergie à un pH donné et d’effectuer un transfert de charge efficace avec le graphène. On obtient ainsi un dopage ajustable, allant d’un fort dopage p à un faible dopage n. Nos résultats révèlent la présence d’un mécanisme de dégradation inattendu relié à l’exposition continue au laser qui suggère une migration de l’hydrogène à la surface pour se concentrer dans la région irradiée. L’évolution des propriétés optiques laisse croire qu’on atteint une densité suffisante d’hydrogène pour modifier la structure de bandes du graphène et le rendre significativement semi-conducteur. Les cartes Raman ont aussi révélé que l’hydrogénation ne semble pas homogène à l’échelle de nos mesures. La densité de défauts a été quantifiée avec deux méthodes différentes qui sont généralement en accord. Au niveau du dopage, notre méthode ne semble pas produire un transfert de charges aussi important que prévu par la loi de Nernst, ce qui pourrait être expliqué par un mauvais contact entre le platine et le graphène. Par contre, on observe en général les tendances prévues dans la littérature, mais avec un décalage en énergie qui pourrait être expliqué par une augmentation du travail de sortie du graphène de 100-200 meV après hydrogénation. / For the past twenty years, graphene has been studied worldwide for its remarkable optoelectronic properties. Despite all these efforts and the apparent simplicity of this monoatomic sheet of carbon, its subtle physics continues to surprise and remains to be discovered. The aim of this exploratory study is to assess the effect of doping and hydrogenation on the Raman spectrum of graphene, in order to better understand the underlying electronic properties. To do this, we are using RIMA, a hyperspectral Raman imager that differs from traditional Raman setups in its ability to rapidly produce Raman maps of around 100 microns on a side, enabling us to spatially resolve the properties of the sample in addition to having a statistical number of spectra. The samples are produced entirely in our laboratories, and each process is controlled and detailed in this thesis. Graphene is synthesized by chemical vapor deposition (CVD), then exposed to a high-temperature atomic hydrogen beam to form C-H bonds on the surface. Doping is generated and controlled simply by immersing the sample in a solution of variable pH, having previously deposited platinum nanoparticles on its surface. The chemical equilibrium involving the redox couple Pt/PtO enables its energy to be fixed for a given pH and an efficient charge transfer to take place with the graphene. This results in an adjustable doping, ranging from high p-doping to low n-doping. Our results reveal the presence of an unexpected degradation mechanism linked to continuous laser exposure, suggesting hydrogen migration across the surface to concentrate in the irradiated region. The evolution of optical properties suggests that a sufficient density of hydrogen is reached to modify the band structure of graphene and render it significantly semiconducting. Raman maps also revealed that hydrogenation does not appear to be homogeneous at the scale of our measurements. Defect density was quantified using two different methods which are in general agreement. In terms of doping, our method does not seem to produce as much charge transfer as predicted by Nernst’s law, which could be explained by poor contact between platinum and graphene. On the other hand, we generally observe the trends predicted in the literature, but with an energy shift that could be explained by an increase in graphene work function of 100-200 meV after hydrogenation.

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