This work investigates fabrication methods of nickel oxide thin films and their use in organic electronics. Two fabrication techniques were studied: UV-ozone oxidation of pure nickel films and reactive RF magnetron sputtering. The former was used to produce Ni/Ni2O3 bi-layer anodes to use as a substitute for the de facto standard ITO anode. OLEDs fabricated using Ni/Ni2O3 bi-layer anodes exhibited comparable device performance to standard ITO devices. UV-ozone oxidation was also used to fabricate Ni2O3 buffer layers for OPVs. Solar cells fabricated using Ni2O3 coated ITO exhibited an enhanced power conversion efficiency of up to 90%. RF magnetron sputtering was used to produce NiOx buffer layers with tunable conductivity and optical transparency for OPVs. Solar cells fabricated using NiOx coated ITO exhibited an enhanced power conversion efficiency of up to 60%. Nickel oxide films have been characterized with various techniques: sheet resistance measurements, optical transmission, XPS, UPS, AFM, and TEM.

Organic electronic devices are receiving growing interest because of their potential to employ lightweight, low-cost materials in a flexible architecture. Typically, indium tin oxide (ITO) is utilized as the transparent positive electrode in these devices due to its combination of high transmission in the visible spectrum and high electrical conductivity. However, ITO may ultimately hinder the full market integration of organic electronics due to its increasing cost, the limited availability of indium, lack of mechanical flexibility, and sustainability with regards to the environment and material utilization. Therefore, alternatives for ITO in organic electronics are currently being pursued. Transparent electrodes comprised of single wall carbon nanotubes (SWNTs) are an appealing choice as a surrogate because of the extraordinary electrical and mechanical properties these 1-D structures posses. As such, the research presented in this dissertation has been conducted to advance the goal of manufacturing SWNT networks with transparent electrode properties that meet or exceed those of ITO. To this end, SWNT films were characterized with regard to the collective and individual optoelectronic properties of the SWNTs that comprise the network. Specifically, corroborative theoretical and experimental observations were employed to expand the understanding of how the optoelectronic properties of polydisperse and monodisperse SWNT networks are enhanced and sustained through chemical treatment and subsequent processing. In addition, the impact of interfacial electrical contact resistance between SWNT electrodes and metallic fingers often used in photovoltaic system applications was elucidated. In summary, the research presented in this dissertation can be leveraged with present state of the art in SWNT films to facilitate future SWNT electrode development.

Nous étudions l'utilisation de l'électronique organique à l'interface du tissu nerveux pour des applications in vitro et in vivo. Le principal objectif est la fabrication d’interfaces neuronales flexibles pour enregistrer l'activité électrophysiologique de cellules neuronales sur de longues durées. À cette fin, nous utilisons du parylène-C comme substrat et le polymère conducteur poly(3,4-éthylène dioxythiophène):poly(styrène sulfonate) pour réduire l'impédance de l'interface cellule/électrode. En utilisant nos matrices de microélectrodes, nous montrons comment améliorer le rendement d'enregistrement avec un modèle 3D in vitro. La formation de clusters cellulaires 3D augmente considérablement le nombre d’enregistrements de potentiels d’action unitaires. In vivo, nous démontrons la fabrication de sondes de support en polymères biodégradables sur nos capteurs flexibles en utilisant une combinaison de polymères alcool polyvinylique et poly(lactique-co-glycolique). Alors que notre support d’insertion en PVA fournit la rigidité nécessaire à la pénétration, le revêtement PLGA retarde la dissolution du support afin de placer précisément les capteurs à l'intérieur du cerveau. Cela nous permet d’enregistrer en profondeur et, dans les conditions idéales, de minimiser les lésions cérébrales par rapport à les sondes traditionnelles rigides. Dans l'ensemble, nous avons réussi à effectuer des enregistrements électrophysiologiques avec nos propres microélectrodes et sondes invasives, améliorant le rendement d'enregistrements in vitro et démontrant que nos support d’insertion biodégradables pénètrent le cerveau. Ces résultats annoncent de prometteuses applications médicales futures. / Neural interfaces are designed to unravel the mysteries of the brain and to restore the functions of paralyzed patients. Despite the success of traditional neural interfaces, these rigid devices are prone to failure within months after surgery. Mechanical mismatch with the soft neural tissue is believed to be one of the main causes. In this thesis, we studied the use of soft organic electronics to interface with neural tissue for both in vitro and in vivo applications. Parylene-based microelectrode arrays (MEAs) and depth probes were made, employing the conducting polymer poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) to reduce the impedance at the cell-electrode interface. In vitro, we thereby showed how to enhance the recording yield of MEAs by creating a three-dimensional model of neurospheres. We further report on the fabrication of a new biodegradable polymer shuttle for flexible depth probes based on the combination of poly(vinyl alcohol) (PVA) and poly(lactic-co-glycolic) (PLGA). In vivo, the PVA/PLGA- shuttled probes were acutely tested in mice and revealed promising electrophysiological results. More research remains necessary to evaluate its long-term function in vivo. In conclusion, our results demonstrate that bioresorbable polymers are capable of providing the required stiffness to penetrate the brain, which shows much promise for future neural applications. This work thereby shows that a long-term functional neural interface is not far from being developed.

Neste trabalho foram estudadas as propriedades optoeletrônicas de dispositivos orgânicos emissores de luz (OLEDs) à base de polímeros conjugados possuindo catodos metálicos depositados por meio da técnica de deposição assistida por feixe de íons (IBAD). O principal objetivo do trabalho é produzir uma interface híbrida metal/polímero não abrupta e estudar os seus efeitos na injeção de elétrons. O uso da técnica IBAD em eletrônica orgânica é incipiente, sendo este o primeiro trabalho no Brasil aplicando-a em eletrônica orgânica. Diversos experimentos exploratórios foram feitos para adequar o uso da técnica a esta nova aplicação. Os dispositivos OLEDs possuem estrutura vertical que consiste de um anodo transparente de óxido de estanho índio (ITO) depositado sobre substrato de vidro; de uma camada transportadora de buracos de Poli (3,4-etilenodioxitiofeno): Poli (estirenosulfonato) (PEDOT:PSS) e de uma camada ativa de polifluoreno (PFO). O catodo de alumínio foi depositado sobre o PFO, utilizando a técnica IBAD, utilizando íons de argônio com energia variando de 0 a 1000eV. Simulações utilizando o código TRIM (Transport of Ions in Matter) foram feitas para avaliar a penetração do Al na camada polimérica, bem como o deslocamento atômico durante o processo IBAD. Medidas de microscopia de fluorescência, fotoluminescência (PL) e espectroscopia Raman foram utilizadas para caracterizar os efeitos dos íons sobre a camada polimérica. As propriedades da interface híbrida foram estudadas variando-se a espessura da camada ativa emissora de luz e introduzindo camadas espaçadoras de polieletrólitos inertes entre o catodo metálico e o PFO. Íons com energia maior que 400 eV produzem a diminuição das propriedades luminescentes do polímero. Por fim, as propriedades de injeção eletrônica do catodo foram estudadas através de medidas de corrente e eletroluminescência em função da voltagem. Os resultados mostraram que houve um expressivo deslocamento da voltagem de injeção (Von) para íons de argônio com energias variando entre 0 e 400 eV. As curvas de corrente versus voltagem são descritas pelo modelo Fowler- Nordheim e possuem características alteradas pelo processo IBAD. Medidas de luminescência e de corrente versus voltagem sugerem a formação de uma interface contendo nanopartículas metálicas isoladas espalhadoras de luz para energias dos íons de argônio entre 0 e 80 eV. Estas nanopartículas favorecem a injeção para campos elétricos menores. A melhora no contato entre o polímero e o catodo é observada e é consistente com a redução de caminhos preferenciais durante a injeção de elétrons, o que minimiza problemas relacionados à eficiência e durabilidade dos OLEDs. / In this work, optoelectronic properties from organic light emitting devices (OLEDs), based on conjugated polymers with metallic cathode, which were deposited by ion beam assisted deposition technique (IBAD) were studied. The main objective of this work is to produce a hybrid non abrupt metal/polymer interface and to study its effects on electron injection. The use of this technique in organic electronics is incipient, being used in Brazil for the first time. Several exploratory experiments were made, to suit this technology to this new application. The OLEDs devices have a typical vertical-architecture, using Indium Tin Oxide (ITO) covered glass substrate as transparent anode; Poly [ethylene-dioxythiophene]: Poly [styrene sulfonic acid] (PEDOT:PSS) as hole transport layer and polifluorene (PFO) as emitting layer. The cathode layer were deposited over the PFO using IBAD with aluminum and Ar ions, with energies in the range from 0 to 1000 eV. Computer simulations using TRIM code (Transport of Ions in Matter) were done to evaluate the Al penetration into the polymer and the atomic displacement during IBAD process. Fluorescence microscopy, photoluminescence (PL) and Raman spectroscopy were used to study the effects of ions on the polymer layer. The hybrid interface properties were studied with the variation of the active layer thickness and introducing spacing layers of inert polyelectrolyte between the metallic cathode and the PFO. Ions with energy above 400eV decrease polymer electroluminescent properties. Finally, electron injection properties of the cathode were studied using Current Voltage and Electroluminescent measurements. The results show that lower Ar+ ion energies (between 0 and 400 eV) cause a significant shift on the injection voltage. The Current Voltage curves, whose characteristics are modified by IBAD, are described by Fowler Nordheim model. These measurements suggests that Ar+ ion energies between 0 and 80 eV promote the formation of an interface that contains isolated metallic nanoparticles, which may scatter the light. These nanoparticles ease the injection for lower electric fields. The enhancement of the contact between polymer and cathode is observed and is consistent with the reduction of preferred paths during electron injection, which minimizes the problems related to OLEDs efficiency and durability.

The literature surrounding organic small-molecule donor-acceptor systems is summarised for a range of optoelectronic applications (OLEDs, OPVs, OFETs etc.). There is a focus on the key building blocks: 1,3,4-oxadiazole (OXD), diphenylamine (DPA), carbazole (Cbz) and fluorene (F). The incorporation of such moieties into various donor-acceptor systems is discussed with further reference to selected alternative organic donor and acceptor systems. The syntheses of novel bipolar molecules based on a donor-spacer-acceptor (DPA/Cbz-F-OXD) structure and the incorporation of these molecules into single-layer OLEDs is presented. It is demonstrated how the emission colour can be tuned from green to deep blue by systematic manipulation of the structure. A significant result is that high efficiency accompanied with pure, deep blue emission in single-layer OLEDs can be achieved with this structural motif. The incorporation of these materials as part of a simple two-component blend to produce white OLEDs is presented and the modification of the materials to improve electron-transport properties is discussed. The synthesis of DPA-bridge-OXD wire systems is presented with the use of oligo-p-phenyleneethynylene units as a bridge of varying length to investigate the effect on charge transfer between the donor and acceptor. Photophysical studies demonstrate the change in absorption, emission and fluorescence lifetimes as the length scale of the molecules is altered. The synthesis of a series of planarised and twisted DPA-bridge-OXD systems based upon phenylene linkers is discussed. Finally, a series of DPA-F-OXD-anchor molecules is presented for incorporation into DSSC devices. The synthesis of these materials is described and the suitability of various anchoring groups for DSSCs is analysed through photophysical and device studies.

Cette thèse est porté sur l'étude du transport électronique dans différents matériaux organiques semi-conducteurs, considérés comme candidats potentiels pour des applications en Electronique de Spin Organique. Pour rendre possible la diffusion d'un courant polarisée en spin à l'intérieur d'un semi-conducteur (injection-transport-détection), le mécanisme de transport et la mobilité des porteurs de charge, ainsi que la nature et la valeur de la résistance de contact de l'interface séparant matériau organique et électrodes métalliques ferromagnétiques, doivent répondre à des critères très stricts. Tous les dispositifs sont en géométrie latérale. Nous étudions trois matériaux organiques différents: des fibres supramoléculaires auto-assemblées, une encre de nana-flocons de graphene exfolié en phase liquide et un polymère semi-conducteur fortement dopé en forme de couche mince. Nos résultats montrent que les conditions sont partiellement respectées, mais que des défis demeurent. / In this thesis, we study the electronic charge transport properties in different high mobility organic semiconductors considered as possible candidates for applications in Organic Spintronics. Stringent conditions are needed to make possible the diffusive transport of a spin-polarized current through an organic spacer (injection-transport-detection): the mechanism of charge transport and the carriers mobility, as well as the interface between the organic semiconductor and the ferromagnetic metallic electrodes, should meet special criteria. Our devices are in lateral geometry. We investigate three organic materials, all compatible with wet processing of organic electronics: supramolecular fibers self-assembled by light irradiation, an ink of liquid-phase exfoliated graphene nano-sheets and a conjugated polymer semiconductor thin film exposed to strong electrochemical doping. We observe that the criteria are partially matched, but some challenges are still present.

La combinaison de la spintronique et de I' électronique organique est censée conduire à une nouvelle gamme d'applications en la domaine de spintronique organique. Ce travail se concentre sur la physique des molécules organiques adsorbées sur des surfaces métalliques, en mettant I' accent sur les changements de leurs structures électroniques en raison de I' effet important du substrat métallique. Nous avons étudié le complexe Ni2 adsorbé sur le Cu qui montre un effet Kondo à basses températures. Nous avons ensuite étudié des chaînes d'oligoacènes (anneaux de benzène fusionnè) qui présentent une propriété prédite: une oscillation de la bande interdite d' énergies en fonction de la longueur de la molécule. Cette propriété peut survivre même lorsque la molécule est adsorbée sur une surface, comme I' Au ou le Si02. Pour terminer, nous avons étudié des petites molécules, telles que l'éthane ou I'éthylène, adsorbées sur un subtrat de Cu et de Co. La différence d' énergie entre I' orbitale vide la plus basse (LUMO) et I' orbitale moléculaire occupée la plus élevée (HOMO) est étudiée dans les approximations de la théorie de la fonctionnelle de la densité (DFT) et la méthode GW. / The combination of spintronics and organic electronics, is believed to lead to a new generation of spin based devices, which would likely open a new broad range of applications in the field of organic spintronics. ln this context, this work focuses on organic molecules adsorbed on metallic surfaces and their electronic structure changes due to the important screening of the metallic environment. We have studied different systems, starting with a Ni2 complex adsorbed on Cu (001), where Kondo effect sets in. This study is followed by oligoacene chains (fused benzene rings) where an extraordinary property is seen: an oscillation of the energy band gap with respect to the molecular length. This property is proved to survive under the screening of surfaces such as Au(111) and Si02. We finally focused on small molecules, like ethane and ethylene, adsorbed on Cu and Co. The difference of energy between the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO) is studied using density functional theory (DFT)and GW methodologies.

Diese Arbeit stellt eine eingehende Studie des sogenannten Vertikalen Organischen Feld-Effekt-Transistors (VOFET) dar, einer neuen Transistor-Geometrie, welche dem stetig wachsenden Bereich der organischen Elektronik entspringt. Dieses neuartige Bauteil hat bereits bewiesen, dass es in der Lage ist, eine der fundamentalen Einschränkungen herkömmlicher organischer Feld-Effekt-Transistoren (OFETs) zu überwinden: Die für Schaltfrequenz und An-Strom wichtige Kanallänge des Transistors kann im VOFET stark reduziert werden, ohne dass teure und komplexe Strukturierungsmethoden genutzt werden müssen. Das genaue Funktionsprinzip des VOFET ist bisher jedoch weitgehend unerforscht. Durch den Vergleich von experimentellen Daten mit Simulationsdaten des erwarteten Bauteil-Verhaltens wird hier ein erstes, grundlegendes Verständnis des VOFETs erarbeitet. Die so gewonnenen Erkenntnisse werden im Folgenden genutzt, um bestimmte Parameter des VOFETs kontrolliert zu manipulieren. So wird beispielsweise gezeigt, dass die Morphologie des organischen Halbleiters, und damit seine Abscheidungsparameter, sowohl für die VOFET-Herstellung als auch für den Ladungsträgertransport im fertigen Bauteil eine wichtige Rolle spielen. Weiterhin wird gezeigt, dass der VOFET, genau wie der konventionelle OFET, durch das Einbringen von Kontaktdotierung deutlich verbessert werden kann. Mit Hilfe dieser Ergebnisse kann gezeigt werden, dass das Funktionsprinzip des VOFETs mit dem eines konventionellen OFETs nahezu identisch ist, wenn man von geringen Abweichungen aufgrund der unterschiedlichen Geometrien absieht. Basierend auf dieser Erkenntnis wird schließlich ein VOFET präsentiert, welcher im Inversionsmodus betrieben werden kann und so die Lücke zur konventionellen MOSFET-Technologie schließt. Dieser Inversions-VOFET stellt folglich einen vielversprechenden Ansatz für leistungsfähige organische Transistoren dar, welche als Grundbausteine für komplexe Elektronikanwendungen auf flexiblen Substraten genutzt werden können. / This work represents a comprehensive study of the so-called vertical organic field-effect transistor (VOFET), a novel transistor geometry originating from the fast-growing field of organic electronics. This device has already demonstrated its potential to overcome one of the fundamental limitations met in conventional organic transistor architectures (OFETs): In the VOFET, it is possible to reduce the channel length and thus increase On-state current and switching frequency without using expensive and complex structuring methods. Yet the VOFET's operational principles are presently not understood in full detail. By simulating the expected device behaviour and correlating it with experimental findings, a basic understanding of the charge transport in VOFETs is established and this knowledge is subsequently applied in order to manipulate certain parameters and materials in the VOFET. In particular, it is found that the morphology, and thus the deposition parameters, of the organic semiconductor play an important role, both for a successful VOFET fabrication and for the charge transport in the finished device. Furthermore, it is shown that VOFETs, just like their conventional counterparts, are greatly improved by the application of contact doping. This result, in turn, is used to demonstrate that the VOFET essentially works in almost exactly the same way as a conventional OFET, with only minor changes due to the altered contact arrangement. Working from this realisation, a vertical organic transistor is developed which operates in the inversion regime, thus closing the gap to conventional MOSFET technology and providing a truly promising candidate for high-performance organic transistors as the building blocks for advanced, flexible electronics applications.

Functional heterojunctions in organic electronic devices are interfaces formed either between a conducting electrode and an organic semiconductor or between two different organic semiconductors in blended and multilayered structures. This thesis is primarily concerned with the energy level alignment and the interfacial electronic structures at functional heterojunctions encountered in electronic devices made with solution-processable semiconducting polymers. Investigations on the electronic structures across these heterointerfaces are performed with the combined use of electromodulation and photoemission spectroscopic techniques. Electromodulation and ultraviolet photoemission spectroscopic techniques enable direct determination of the surface work functions of electrodes at the electrode/semiconducting polymer interfaces. We overcame the inherent problems faced by electromodulation spectroscopy, which undermine accurate determination of interfacial electronic structures, by performing electroabsorption (EA) measurements at reduced temperatures. We showed in this thesis that low-temperature EA spectroscopy is a surface sensitive technique that can determine the interface electronic structures in electrode/polymer semiconductor/electrode diodes. Using this technique, we demonstrated that the energy level alignments in these solution-processed organic electronic devices are determined by the surface work functions of passivated metals rather than by those of clean metals encountered in ultrahigh vacuum. This thesis also discloses our studies on the electronic structures in polymeric diodes with type II donor-acceptor heterojunctions using the EA spectroscopy. We showed that minimising meausurement temperature and attenuating EA illumination intensity enable accurate determinations of the electronic structures in these devices. We demonstrated that the electronic structures and the performance characteristics of multilayered polymer light-emitting diodes are also determined by the surface work functions of passivated metals. Our investigations confirm that electronic doping of the organic active layers, rather than minimisation of the Schottky barriers at electrode/polymer contacts, holds the key in realising high-performance organic light-emitting devices.

L’électronique organique connaît depuis ces dernières années un fort développement. Le CEA LITEN dispose d’une technologie d’impression par sérigraphie de transistors de type N et de type P sur une même plaque, permettant de créer des circuits complémentaires. Les performances et les limitations de cette technologie ont été étudiées, l’un des objectifs principaux de cette thèse étant de réaliser une étude concernant la faisabilité d’une étiquette RFID entièrement réalisée en technologie organique imprimée. Une telle étiquette, en plus d’être flexible, possèderait un coût de fabrication extrêmement bas.Des blocs entiers couramment utilisés dans les circuits RFID et comportant jusqu’à 50 transistors sont conçus et testés, montrant des performances supérieures ou au niveau de l’état de l’art dans ce domaine. La technologie organique imprimée n’étant pas aussi mature que celle utilisée dans la filière semi-conductrice classique, une étude est également menée concernant les effets de la dispersion du procédé de fabrication et du vieillissement sur les performances des circuits. Des pistes seront ainsi définies sur les paramètres (fiabilité, mobilité dans les semi-conducteurs organiques, taille des dispositifs…) à améliorer pour permettre à l’électronique organique de venir concurrencer l’industrie du silicium. / During the past few years, the field of organic electronics has known an important development. The CEA LITEN is able to manufacture N-type and P-type screen-printed transistors on a same plastic sheet, enabling the design of complementary circuits. The performances and limitations of this technology are studied since one of this thesis’ main objectives is to determine the feasibility of a fully-printed organic RFID tag. Such a tag would be flexible and could be manufactured at an extremely low-cost. Some circuits commonly used in the RFID tags, and using up to 50 transistors, are designed and tested, showing some performances equivalent or above the reported latest developments. The organic electronics manufacturing process is not as mature as the one used in the classical silicon industry. Therefore, a study is performed concerning the effects of this process scattering, as well as the ageing, on the circuits’ performances. The main improvements (in terms of reliability, organic semi-conductor mobility, size) that can help the organic electronics in order to compete, one day, with the silicon industry, are discussed.