Ce travail de thèse décrit l’alignement par pulvérisation de nanofils d'argent (AgNWs) aux interfaces solides sous la forme de films mono- et multicouches. Cette technique permet de contrôler la densité de nanofils dans le plan sur des zones macroscopiques avec des paramètres d'ordre nématique atteignant des valeurs > 0,90 dans les films monocouches. La répétition des cycles de dépôt en utilisant l’assemblage couche-par-couche produit des films multicouches dans lesquels par exemple des superstructures uniaxiales ou hélicoïdales peuvent être préparées en choisissant les directions de pulvérisation appropriées pour chaque monocouche individuelle. Les systèmes uniaxiaux sont des polariseurs fortement dépendant de la longueur d'onde (en raison de l'orthogonalité des plasmons transversaux et longitudinaux des AgNWs) et montrent une conductivité anisotrope dans le plan. Les systèmes hélicoïdaux montrent un dichroïsme circulaire très élevé qui peut être ajusté par exemple par le biais de la densité des AgNWs dans le plan ou de la distance entre les monocouches individuelles. Les mesures de la matrice Müller confirment que le dichroïsme circulaire observé découle de la superstructure hélicoïdale des multicouches à base d’AgNWs. / This thesis work describes the spray-alignment of silver nanowires (AgNWs) at solid interfaces in the form of mono- and multilayer films. The technique allows to control the in-plane density of nanowires over macroscopic areas with the best nematic order parameters reaching > 0.90 in monolayer films. Repeated deposition cycles using layer-by-layer assembly yield multilayer films in which for example uniaxial or helically twisted superstructures can be prepared by choosing appropriate spraying directions for each individual monolayer. Uniaxial systems are strong wavelength dependent polarizers (due to the orthogonality of the transversal and longitudinal plasmons of the AgNWs) and they show anisotropic in-plane conductivitiy. Helically twisted systems show very high circular dichroism which can be tuned for example through the in-plane density of AgNWs or through the distance between individual monolayers. Müller Matrix measurements confirm that the observed circular dichroism arises from the helically twisted superstructure of the AgNW multilayers.

The aim of this work was to investigate silver nanowire as well as carbon nanotube networks as transparent conducting electrodes for small molecule organic solar cells. In the framework of the nanowire investigations, a low-temperature method at less than 80 °C is developed to obtain highly conductive networks directly after the deposition and without post-processing. In detail, specific non-conductive organic materials act as a matrix where the nanowires are embedded in such that a mutual attraction based on capillary forces and hydrophobic interaction is created. This process is mediated by the ethanol contained in the nanowire dispersion and works only for sublayer materials which exhibit hydrophobic and hydrophilic groups at the same time. In contrast to high-temperature processed reference electrodes (210 °C for 90 min) without matrix, a slightly lower sheet resistance of 10.8 Ohm/sq at a transparency of 80.4 % (including substrate) is obtained by using polyvinylpyrrolidone as the sublayer material. In comparison to annealed silver nanowire networks, the novel approach yields a performance enhancement in corresponding organic solar cells which can compete with ITO-based devices. Furthermore, a novel approach for scalable, highly conductive, and transparent silver nanowire top-electrodes for organic optoelectronic devices is introduced. By utilizing a perfluorinated methacrylate as stabilizer, silver nanowires with high aspect ratio can be transferred into inert solvents which do not dissolve most organic compounds making this modified dispersion compatible with small molecule and polymer-based organic optoelectronic devices. The inert silver nanowire dispersion yields highly performing top-electrodes with a sheet resistance of 10.0 Ohm/sq at 80.0 % transparency (including substrate) directly after low-temperature deposition at 30 °C and without further post-processing. In comparison to similarly prepared reference devices comprising a thin-metal film as transparent top-electrode, reasonable power conversion efficiencies are demonstrated by spray-coating this dispersion directly on simple, air-exposed small molecule-based organic solar cells. Moreover, a deeper understanding of the percolation behavior of silver nanowire networks has been achieved. Herein, direct measurements of the basic network parameters, including the wire-to-wire junction resistance and the resistance of a single nanowire of pristine and annealed networks have been carried out for the first time. By putting the values into a simulation routine, a good accordance between measurement and simulation is achieved. Thus, an examination of the electrical limit of the nanowire system used in this work can be realized by extrapolating the junction resistance down to zero. The annealed silver nanowires are fairly close to the limit with a theoretical enhancement range of only 20 % (common absolute sheet resistance of approximately 10 Ohm/sq) such that a significant performance improvement is only expected by an enlargement of the nanowire length or by the implementation of new network geometries. In addition, carbon nanotube networks are investigated as alternative network-type, transparent bottom-electrode for organic small molecule solar cells. For that purpose, cleaning and structuring as well as planarization procedures are developed and optimized which maintain the optoelectronic performance of the carbon nanotube electrodes. Furthermore, a hybrid electrode consisting of silver nanowires covered with carbon nanotubes is fabricated yielding organic solar cells with only 0.47 % power conversion efficiency. In contrast, optimized electrodes comprising only carbon nanotubes show significantly higher efficiency. In comparison to identically prepared ITO devices, comparable or lower power conversion efficiencies of 3.96 % (in p-i-n stack), 4.83 % (in cascade cell) as well as 4.81 % (in p-n-i-p architecture) are demonstrated. For an inverted n-i-p stack design, the highest power conversion efficiency of 5.42 % is achieved.

Electronic devices define our everyday lives. They are often large, rigid, and brittle. Modern medical science has come so far as to start using miniature electronic devices to monitor many types of diseases. Especially, neurological disorders pose obstacles hard to overcome when treating them but it also motivates finding methods that allow for continuous monitoring. Implementing a small electronic device inside the human body adds requirements on the device to be stretchable, biocompatible, and more. Not only is the device limited by these factors, but also, current fabrication methods are not efficient for creating nanoscale versions for these types of devices. patterninglaser ablation is a growing field for cutting out and pattern nano-materialistic devices with high precision and good repeatability. This project is focused on using a laser engraving tool from metaquip on different substrates. This project is focused on the development of methods for laser fabrication of soft neural electrodes. The requiered steps are the alignment of samples to assure good precision when engraving it with the laser engraving tool, that also will be called “laserpatterner”, finding good parameters for cutting out devices and pattern conductors for said devices. On top of that, a linear force stretching will be used to characterize samples that were cut, in the form of strips, using the laserpatterner. The stretching behavior of strips consisting of the elastomer polydimethylsiloxane, which in turn will be the insulator for silver nanowires, is examined in the stretching setup. Parameter optimization is relevant in all experiments done in this project and lay the foundations for cutting and patterning silver nanowires devices. All factors included will eventually lead to a good method for fabricating soft neural electrode devices and this project is stepping stone towards that goal. / <p>Examensarbetet är utfört vid Institutionen för teknik och naturvetenskap (ITN) vid Tekniska fakulteten, Linköpings universitet</p>

Ce travail de thèse est principalement dédié à la mise en forme et à l’utilisation de nano-objets unidimensionnels comme matériaux d’électrodes transparentes. Les nanofils d’argent font partie des candidats les plus prometteurs pour le remplacement de l’oxyde d’indium-étain, actuellement le plus répandu dans les dispositifs commerciaux. La forte instabilité des nanofils d’argent à l’oxydation est néanmoins un problème critique puisque les électrodes deviennent moins performantes en peu de temps. En premier lieu, la triphénylphosphine a été utilisée comme agent inhibant l’oxydation. Contrairement aux électrodes non modifiées, celles-ci sont stables pendant plus de trois mois. Une deuxième partie est consacrée à l’utilisation de l’électrofilage pour élaborer des électrodes transparentes à base de nanofibres de matériaux conducteurs (nanofibres de cuivre, nanotubes de carbone, oxyde de graphène réduit). Enfin, une dernière partie concerne l’étude des propriétés mécaniques de nanofibres d’alcool polyvinylique par l’écoulement d’un fluide porteur dans une constriction réalisée en impression 3D. Cette méthode permet une analyse et une évaluation simple et rapide de la contrainte à la rupture des nanofibres, propriété difficilement accessible par des mesures mécaniques traditionnelles. / This PhD work deals mainly with the high scale organization and use of unidimensional nano-objects for making transparent electrodes. Among the candidates of choice for the replacement of indium tinoxide, the main material used in commercial devices, silver nanowires (Ag NW) are among the most promising. However, the tendency of silver nanowires to be quickly oxidized can severely affect their performances. Firstly, this drawback is circumvented through the use of triphenylphosphine (PPh3)as a protective agent. Unlike bare Ag NW electrodes, the PPh3 modified Ag NW electrodes are stable over three months. A second part is dedicated to the production of transparent electrodes via the electrospinning technique. Materials such as copper nanofibers, carbon nanotubes and reduced graphene oxide are investigated. The last part of the manuscript deals with the measurement of the mechanical properties of poly(vinyl alcohol) (PVA) nanofibers. To do so, the flowing of a fluid in a3D-printed constriction is used. Usually determined with difficulty, the fracture strength of the nanofibers can be evaluated quickly at ease.

Ce travail propose une optimisation de la conductivité électrique transverse des composites structuraux matrice/fibres de carbone. L'influence de la fonctionnalisation électrique de l'ensimage sur la conductivité des composites est particulièrement étudiée. Des feuillets submicroniques d'argent (AgNpts) ont été élaborés en présence de citrate de sodium (TSC). Leur morphologie plane est particulièrement adaptée à une dispersion dans un ensimage. Les feuillets ont été dispersés dans une matrice modèle. Le seuil de percolation électrique des feuillets est déterminé à 5,9 %. Cette valeur est cohérente avec un facteur de forme modéré, compris entre 12 et 28. L'ensimage fonctionnalisé a ensuite été déposé sur une mèche de fibres de carbone, elle-même imprégnée par une matrice PAEK hautes performances. Avant imprégnation des fibres de carbone, des fils submicroniques d'argent ont été introduits dans la matrice PAEK. Des composites matrice-fils submicroniques d'argent/fibres de carbone avec ensimage conducteur ont été mis en œuvre. Leur conductivité électrique est élevée (7 S.m-1), alors que la fraction volumique en particules d'argent (fils et feuillets) est inférieure à 1 % en volume. / This PhD thesis deals with the optimization of transverse electrical conductivity of Thermoplastic Carbon Fiber Reinforced Polymer. The influence of an electrically conductive sizing has been investigated. Silver nanoplates (AgNpts) have been successfully synthesized by a soft chemical reduction, with trisodiumcitrate (TSC) as surfactant. Silver nanoplates have been dispersed into a model matrix, percolation threshold has been determined near 5.9 % in volume fraction. This value is consistent with their moderate aspect ratio (between 12 and 28). Size and morphology of silver nanoplates are suitable for their dispersion in the sizing. Carbon fiber has been coated with conductive sizing. Carbon fiber will be further impregnated by a PAEK thermoplastic matrix. A higher conductivity level has been achieved by introducing silver nanowires in the PAEK matrix. Structural composites consisting of matrix-silver nanowires / continuous carbon fiber sized with conductive sizing have been elaborated. Their electrical conductivity reached 7 S.m-1 for a total silver volume fraction of 1 %.vol.

The main focus of this thesis work has been the study of domain wall (DW) dynamics in disordered cylindrical nanomagnets. The study attempts to accurately quantify the stochasticity associated with driven (temperature/magnetic field/spin-torque) DW kinetics. Our results as summarized below, are particularly relevant with regard to the technological advancement of DW based magnetoelectronic devices. 1. Temperature dependent noise measurements showed an exponential increase in noise mag-nitude, which was explained in terms of thermally activated DW depinning within the Neel-Brown framework. The frequency-dependence of noise also indicated a crossover from nondiffusive kinetics to long-range diffusion of DWs at higher temperatures. We also observed strong collective depinning, which must be considered when implementing these nanowires in magnetoelectronic devices. 2. Our noise measurements were sensitive enough to detect not only the stochasticity in DW propagation (diffusive random walk) but also their nucleation in the presence of magnetic field down to a single DW unit inside an isolated single Ni nanowire. Controlled injection and detection of individual DWs is critical in designing DW based memory devices. 3. The spectral slope of noise was observed to be sensitive to DWkinetics that reveals a creep-like behavior of the DWs at the depinning threshold, and diffusive DW motion at higher spin torque drive. Different regimes of DW kinetics were characterized by universal kinetic exponents. Noise measurements also revealed that the critical current density and DW pinning energy can be significantly reduced in a magnetically coupled vertical ensemble of nanowires. This was attributed to strong dipolar interaction between the nanowires. Our results are particularly important in view of recent proposals for low power consumption magnetic storage devices that rely on DW motion. In all our experiments, the critical magnetic field/current density, required to set the DWs in duffusive kinetics, were found to be much smaller than the reported values for nanostrips. This could be attributed to the circular cross section of nanowires, where massless DWs results in the absence of Walker breakdown and hence in zero critical current density. At present the contribution from the non-adiabaticity, which acts as an effective field and can reduce the crit- ical current density, can not be denied. The main di±culty in quantifying the non-adiabatic spin-torque is that not only does it contain contributions due to non-adiabatic transport but also due to spin-relaxation provided by magnetic impurities or the sources for spin-orbit scattering. Fortunately, in cylindrical nanomagnet, non-adiabaticity does not affect the DW motion. There- fore, cylindrical NWs may be promising candidate for future magnetic storage devices. However, a systematic experimental study of DW dynamics in cylindrical nanomagnets is lacking. In chapter 7, silver nanowires (AgNWs) are shown to be stabilized in fcc or hcp crystal structure, depending on the electrochemical growth conditions. The AgNWs stabilized in hcp crystal structure are shown to exhibit exotic structural properties i.e. ultra low noise level, thermally driven unconventional structural phase transformation, and time dependent structural relaxation. Ultra noise level makes hcp AgNWs suitable for application in nanoelectronics and the structural transformation may be exploited for use in smart materials. Though time resolved transmission electron microscopy and noise measurements provide some understanding of the hcp AgNWs formation, the precise growth mechanism is still not clear. Future scope of the work The results in this thesis provide the groundwork for a good understanding of stochastic DW kinetics in isolated as well as ensemble of magnetic nanocylinders. Some extensions to this work that would help expand and strengthen the results, are listed below; 1. In all the nanocylinders used for our experiments the source of stochasticity in DWkinetics were randomly distributed structural defects. For a controlled injection and detection of DWs between the voltage probes, it would be of great importance to fabricate artificial notches (pinning centers) in the NW. These notches can be fabricated either by using nano-indentation or by a focussed ion beam. 2. To investigate whether DWs in different parts of the nanowire exhibit spatio-temporal correlation, a simultaneous detection of DWkinetics (through noise measurement) between different volage probes needs to be done. If the propagation time of DWs scales with the distance between the voltage probes, we can be confident of our velocity measurement. Then, by recording the DWvelocity as function of eld/current for nanowire (or nanostrip) absence (or presence) of the Walker breakdown can be probed. This would be a significant result for future spintronic devices. With an accurate determination of velocity even non- adiabaticity parameter may be calculated and one can see its effect on DW dynamics. 3. A complete understanding of sustained avalanches at finite magnetic fields, characterized by a high spectral exponent (a>¸ 2:5) in an ensemble of nanowires is still lacking. Per- forming a controlled experiment on a single nanowire, by varying the number of nanowires in the alumina matrix, one can study the chaotic dynamics of DWs in the ensemble in very accurate manner. All the experiments on AgNWs were performed on ensembles. The large change in a as well as noise magnitude in hcp AgNWs could arise from stress relaxation due to the presence of an insulating matrix or structural relaxation, determined by the nanowire growth kinetics. To resolve this issue, time and temperature dependent noise measurements should be performed on single nanowire stabilized in both hcp and fcc crystal structure.

Organic solar cells (OSCs) is an emerging photovoltaic technology that opens up new application areas where common inorganic techniques are not able to score. Some of those key features are flexibility, light weight, semitransparency, and low cost processing. The current industry-standard for the transparent electrode, indium tin oxide (ITO), cannot provide these properties because it is brittle and expensive. This thesis aims to investigate an alternative type of promising transparent electrode: silver nanowire (AgNW) networks. They exhibit similar or even better optical and electrical performance than ITO down to a sheet resistance of 12 Ohm/sq at 84% transmission (including the glass substrate). Furthermore, AgNWs are more flexible, solution-processable, and more cost-effective than ITO. However, two challenges occur during implementation as bottom electrode in OSCs. First, their inherently high roughness causes devices to shunt. Second, the AgNW network structure exhibits – in contrast to the continuous ITO – µm²-sized voids that have to be bridged electrically by the organic layers. In the first part of this thesis, solution-processed small molecule charge transport layers are investigated. In the case of hole transport layers (HTL), the host BF-DPB and the dopant NDP9 are investigated using tetrahydrofuran as a solvent. It is shown that BF-DPB is already doped by NDP9 in solution via the formation of a hybrid molecule complex. Solution-processed layers exhibit similar conductivities as compared to the reference deposition, which is thermal evaporation in high vacuum. The layers sufficiently smoothen the AgNW electrode such that DCV5T-Me:C60 organic solar cells with an efficiency up to 4.4% are obtained. Moreover, the influence of the square micrometer large network voids is investigated using HTLs of varying conductivity. As a result, a minimum conductivity of 1e−4 S/cm is needed to avoid macroscopic performance losses. Equivalent circuit simulations are performed to confirm these results. As a second planarization method, the AgNWs are buried in an insulating polymer that serves concurrently as flexible and ultrathin substrate. Out of three different polymers tested, the optical adhesive ’NOA63’ gives the best results. The roughness is strongly reduced from 30 nm down to (2 ± 1) nm. Two different OSC types are employed as testing devices with fully-flexible alumina encapsulation against moisture ingress. Maximum power conversion efficiencies of 5.0% and 5.6% are achieved with a fullerene-free cascade layer architecture and a DCV5T-Me:C60 OSC, respectively. To evaluate the applicability of these fully-flexible and encapsulated devices, degradation studies are performed under continuous illumination and a humid climate. Although employing the intrinsically stable DCV5T-Me:C60 stack design, within one day a fast degradation of the fully-flexible solar cells is observed. The degradation is attributed to AgNW electrode failure that results from photo-oxidation and -sulfurization, photo-migration, and electromigration. It is further shown that the cascade organic solar cell lacks intrinsic stability. In summary, efficient, fully-flexible, and encapsulated devices are shown. However, in terms of competitive OSCs, the low stability of AgNW electrodes is a challenge to be taken care of. In current research, this issue needs to be addressed more frequently. / Organische Solarzellen (OSZ) sind ein junges Forschungsgebiet der Photovoltaik, welches neue Anwendungsgebiete erschließt, für die herkömmliche anorganische Solarzellen nicht einsetzbar sind. Einige der Haupteigenschaften sind Flexibilität, niedriges Gewicht, Teiltransparenz und geringe Herstellungskosten. Indiumzinnoxid (ITO), der aktuelle Industriestandard transparenter Elektrodentechnologie, ist nicht in der Lage, diese Eigenschaften zu gewährleisten. Dies liegt vor allem an der Brüchigkeit von ITO und der begrenzten Verfügbarkeit von Indium, welche mit einem hohen Preis einhergeht. Das Ziel dieser Dissertation ist die Integration einer alternativen und vielversprechenden Elektrodentechnologie: Netzwerke aus Silbernanodrähten (AgNWs). Mit einem Schichtwiderstand von 12 Ohm/sq bei einer Transmission von 84% (inklusive Glassubstrat) besitzen sie ähnliche oder sogar bessere optische und elektrische Eigenschaften als ITO. Des Weiteren sind AgNW-Elektroden flexibler und kostengünstiger als ITO und aus flüssiger Phase prozessierbar. Es gibt allerdings zwei Herausforderungen, welche die Integration als Grundelektrode in OSZ erschweren. Zum einen sind AgNW-Netzwerke sehr rauh, sodass organische Bauteile kurzgeschlossen werden. Zum anderen weisen AgNW-Elektroden, im Gegensatz zu einer vollflächigen ITO-Schicht, Lücken zwischen den einzelnen Drähten auf. Diese Lücken müssen von den organischen Schichten der OSZ elektrisch überbrückt werden. Im ersten Teil der Arbeit werden daher flüssigprozessierte Ladungsträgertransportschichten aus kleinen Molekülen untersucht, welche die AgNW-Elektroden glätten und die verhältnismäßig großen Lücken füllen sollen. Im Falle von Lochleitschichten (HTL) wird BF-DPB als Matrix und NDP9 als Dotand in Tetrahydrofuran gelöst und zur Anwendung gebracht. BF-DPB wird dabei schon in Lösung von NDP9 dotiert, wobei sich ein Hybridmolekülkomplex ausbildet. Die Leitfähigkeit der entstehenden Schichten ist ähnlich zu Referenzschichten, die durch thermisches Verdampfen im Hochvakuum hergestellt wurden. Die erhaltenen HTLs glätten die AgNW-Elektroden, sodass DCV5T-Me:C60-Solarzellen mit einer Effizienz von maximal 4.4% hergestellt werden können. Weiterhin wird der Einfluss der quadratmikrometergroßen Löcher auf die makroskopische Effizienz der Solarzelle in Abhängigkeit der HTL Leitfähigkeit untersucht. Um signifikante Effizienzverluste zu verhindern, muss der HTL eine minimale Leitfähigkeit von etwa 1e−4 S/cm aufweisen. Simulationen eines Ersatzschaltkreises bestätigen hierbei die experimentellen Ergebnisse. Im zweiten Teil der Arbeit wird eine Planarisierungsmethode untersucht, in welcher die AgNWs in nichtleitfähigen Polymeren eingebettet werden. Diese Polymere fungieren anschließend als flexibles Substrat. Der optische Kleber ”NOA63” erzielt hierbei die besten Ergebnisse. Die Rauheit der AgNW-Elektroden wird von etwa 30 nm auf 1 bis 3 nm stark reduziert. Anschließend werden diese AgNW-Elektroden in zwei unterschiedlichen OSZ Konfigurationen getestet und mit einer vollflexiblen Schicht aus Aluminiumoxid gegen Wasserdampfpermeation verkapselt. Somit können maximale Effizienzen von 5% mithilfe einer organischen Kaskadenstruktur und 5.6% mit DCV5T-Me:C60 OSZ erreicht werden. Um die Anwendbarkeit dieser vollflexiblen und verkapselten OSZ zu bewerten, werden Alterungsstudien unter konstanter Beleuchtung und feuchtem Klima durchgeführt. Es wird gezeigt, dass die in das Polymer eingebettete AgNW-Elektrode aufgrund von Photooxidation und -schwefelung und Photo- und Elektromigration instabil ist. Dieser Sachverhalt ist für die Anwendung von AgNW-Elektroden in kommerziellen OSZ von großer Bedeutung und wurde in der Forschung bisher nicht ausreichend thematisiert.

We present a novel top-electrode spray-coating process for the solution-based deposition of silver nanowires (AgNWs) onto vacuum-processed small molecule organic electronic solar cells. The process is compatible with organic light emitting diodes (OLEDs) and organic light emitting thin film transistors (OLETs) as well. By modifying commonly synthesized AgNWs with a perfluorinated methacrylate, we are able to disperse these wires in a highly fluorinated solvent. This solvent does not dissolve most organic materials, enabling a top spray-coating process for sensitive small molecule and polymer-based devices. The optimized preparation of the novel AgNW dispersion and spray-coating at only 30 °C leads to high performance electrodes directly after the deposition, exhibiting a sheet resistance of 10.0 Ω □−1 at 87.4% transparency (80.0% with substrate). By spraying our novel AgNW dispersion in air onto the vacuum-processed organic p-i-n type solar cells, we obtain working solar cells with a power conversion efficiency (PCE) of 1.23%, compared to the air exposed reference devices employing thermally evaporated thin metal layers as the top-electrode.

Inkjet printing has attracted much attention in recent years as a versatile manufacturing tool, suitable for printing functional materials. This facile, low-cost printing technique with high throughput and accuracy is considered promising for a wide range of applications including but not limited to optical and electronic devices, sensors, solar cells, biochips, and displays. The performance of such functional devices is significantly influenced by the deposit morphology and printing resolution. Therefore, fabrication functional devices with precise footprints by inkjet printing requires deep understanding of ink properties, material interactions, and material self-assembly. In conventional inkjet printing process, where sessile droplets are directly printed on substrates, particle depositions are usually associated with the well-known, undesirable coffee-ring effect due to the high solvent evaporation rate at the edges of the printed droplets. Such particle accumulation phenomenon in vicinity of the three-phase contact lines of sessile droplets is considered detrimental to inkjet printing applications. This study investigates the material interactions and self-assembly of colloidal inks in inkjet printing applications at different length scales. The potential of inkjet printing has been exploited through employing the dual-droplet inkjet printing of colloidal particles to investigate the self-assembly of colloidal nanoparticles at the air-liquid interface and at the three-phase contact line of sessile droplets, which provide better understanding of the particle deposition morphologies after solvent evaporation. Different from conventional inkjet printing, the dual-droplet printing involves jetting wetting droplets, containing colloidal nanoparticles dispersed in solvents with high vapor pressure, over supporting droplets composed of water only. By tuning the surface tensions and controlling the jetting parameters of the jetted droplets, monolayers with closely-packed deposition of colloidal nanoparticles are demonstrated. Various solutions are proposed to totally suppress or mitigate the coffee-ring effect in inkjet printing applications through tuning the pH value of the supporting droplets in the dual-droplet inkjet printing to control the multibody interactions (i.e., particle-particle, particle-interface, and particle-substrate interactions) or by applying magnetic field to direct the self-assembly of colloidal particles in conventional inkjet printing. In addition, the influence of various forces such as drag force, van der Waals force, electrotactic force, and capillary force on the particle deposition and assembly in vicinity of the three-phase contact line area were investigated for both the conventional and dual-droplet inkjet printing techniques. Finally, fabrication of functional devices such as stretchable conductors have also been demonstrated by inkjet printing of silver nanowires into elastomer substrate, where the viscous liquid elastomer layer shaped the printed silver wire lines into tens of micrometers in dimeter. The silver nanowires align along the printing direction during solvent evaporation, resulting in wires with good mechanical stability and electrical performance. The printing techniques and the outcomes presented in this study can be harnessed in engineering and manufacturing a wide range of technological applications ranging from high-performance optical and electronic devices to stretchable conductors and sensors.

Les travaux de cette thèse sont en rapport avec la caractérisation de cellules solaires organiques et se déclinent suivant 3 axes :- Dans le cadre du projet IMPCELPHOTOR, nous avons développé un banc de caractérisation LBIC/LBIV permettant de cartographier des dispositifs OPV afin de visualiser et d’identifier les défauts de fonctionnement.- Dans le cadre du projet Européen SPrinTronics, nous avons travaillé sur l’amélioration des électrodes. Pour l’électrode collectrice d’électrons, nous avons sélectionné, testé et validé des encres métalliques à base de nanoparticules d’argent compatibles avec l’impression jet d’encre et permettant de réaliser des dispositifs OPV fonctionnels. Pour l’électrode collectrice de trous, nous avons testé des encres à base de nanofils d’argent et de nanotubes de carbone afin de remplacer l’ITO. Des résultats satisfaisants ont été obtenus avec une encre à base de nanofils d’argent. Cette dernière permet de réaliser des cellules semi-transparentes fonctionnelles sur verre et sur plastique. - Un travail sur l’aspect couleur d’un dispositif OPV a été mené au sein du projet PHASME. Nous avons mis en œuvre différentes techniques afin de modifier la couleur d’un dispositif OPV sans détruire ses performances photovoltaïques, le but étant de réaliser des modules polychromes. Nous avons développé simultanément un logiciel de colorimétrie permettant de contrôler et de prévoir le rendu de couleur dû à l’ajout de filtre coloré sur le dispositif OPV. / The work of this thesis is related to the characterization of organic solar cells and is structured in three independant parts :- Within the IMPCELPHOTOR project, we developed an experimental bench based on LBIC/ LBIV mapping, in order to visualize and identify defects within OPV device and modules.- Within the European SPrinTronics project, we worked on the improvement of OPV electrodes. For the top electrode, we selected, tested, and validated metallic inks based on silver nanoparticles compatible with inkjet printing. For the bottom electrode, we tested silver nanowires and carbon nanotubes inks to replace ITO. Satisfactory results have been obtained with an ink based on silver nanowires, which allowed us to obtain functional semi-transparent cells on glass and plastic.- Within the PHASME project, we worked on the visual aspect of a coloured OPV device. We implemented various strategies to change the color of an OPV device without altering its photovoltaic performance, the aim being to achieve full color modules. Simultaneously, we developed a colorimetric software to control and predict the color rendering on the final device (OPV plus filter).