Organic solar cells and organic light emitting diodes are on the forefront of emerging technologies aimed at harnessing light in ways never thought possible. Largear installations of OLED solid state lighting (SSL), as well as organic photovoltaics(OPVs), will become possible as the efficiencies of these devices continue to rise. All organic solar cells and OLEDs require the use of transparent conductive electrodes.Indium oxide (ITO) is currently the transparent conductor of choice for these applications, due to its unique combination of transparency, high conductivity, durability,and favourable surface properties. Indium, however, is a rare and expensive metal; proposed large-area installations of OPV cells and OLEDs will add further strain to global indium supply. Transparent conductive materials that are abundant, inexpensive, and which enable efficient and robust organic devices must therefore be developed. In the present work, suitable ITO anode replacement materials are demonstrated for OLEDS, small-molecule, polymer, and PbS colloidal quantum dot photovoltaics.

Organic solar cells and organic light emitting diodes are on the forefront of emerging technologies aimed at harnessing light in ways never thought possible. Largear installations of OLED solid state lighting (SSL), as well as organic photovoltaics(OPVs), will become possible as the efficiencies of these devices continue to rise. All organic solar cells and OLEDs require the use of transparent conductive electrodes.Indium oxide (ITO) is currently the transparent conductor of choice for these applications, due to its unique combination of transparency, high conductivity, durability,and favourable surface properties. Indium, however, is a rare and expensive metal; proposed large-area installations of OPV cells and OLEDs will add further strain to global indium supply. Transparent conductive materials that are abundant, inexpensive, and which enable efficient and robust organic devices must therefore be developed. In the present work, suitable ITO anode replacement materials are demonstrated for OLEDS, small-molecule, polymer, and PbS colloidal quantum dot photovoltaics.

The use of gold-based nanoparticles and thin films is very promising when it comes to improving several green nanotechnologies. Therefore, in order to further their use in applications such as electrochromic devices, photovoltaics, light-emitting diodes and photocatalysis, the aim of this work was to study the growth of gold-based nanoparticles and thin films. All depositions were made using DC magnetron sputtering, and optical, structural, electrochemical, electrical and photocatalytic studies of the films and particles were performed. The various applications yield a variety of substrate properties, and how these substrate properties affect gold coalescence was studied by depositing gold on glass slides and on SnO2:In, ITO and TiO2 base layers. Temperature also affects the gold coalescence. Therefore, gold was deposited on heated and non-heated substrates, where the latter were also post-heated, with a temperature range between 25ºC and 140ºC in both cases. Various temperatures were also used for manufacturing gold nanoparticles, and their effect as photocatalytic improvers was tested on WO3 films. The optical properties of Au films on glass were determined by ellipsometry in the 0.25 – 2 µm range, and then a spectral density analysis was performed of the effective dielectric permittivity. This work showed that thin gold films are excellent replacements for oxide-based transparent conductors in electrochromic devices. It was also shown that thin homogeneous gold films were better conductors when they were deposited on glass, compared to when they were deposited on oxide base layers, regardless of the optical, electrical and structural properties, or the doping concentration of the base layers. The results also showed that thin gold films were durable at 76ºC, and hence hold for a typical window temperature of ~70ºC. For higher temperatures, gold deposition on heated and non-heated substrates resulted in a distinct difference in growth, and there was also a distinct difference between post-heated gold films produced at 25ºC, compared to when the films were deposited on heated substrates. In the latter case, an island structure was obtained at 140ºC. Spectral density analysis gave spectral densities of similar shape for nanoparticles and continuous gold films, which is useful information for further investigations.

In this thesis the properties of graphene and its few-layers are engineered to make them highly conductive. Two different approaches were implemented to achieve this goal. One approach was to increase the concentration of charge carriers by intercalation of acceptor FeCl3 molecules between graphene planes. This resulted in a highly conductive yet transparent material which can be useful for applications. Another approach was to increase the mobility of carriers by means of removing surface contamination in the current annealing process. Optimal annealing parameters were found and a reproducible cleaning method was suggested.

L'utilisation de matériaux conducteurs transparents (TCM) a rapidement augmenté au cours des deux dernières décennies en raison de la demande croissante liée à l'usage d'appareils électroniques personnels ainsi qu'au développement de cellules solaires à base de couches minces. Jusqu'à présent, le TCM le plus couramment utilisé a été l'oxyde d'indium et d'étain (ITO), mais l'indium est une terre rare dont l'environnement géopolitique lié à son approvisionnement et à sa production est complexe. En outre, la famille des oxydes transparents conducteurs possèdent de médiocres propriétés mécaniques (associée à une fragilité mécanique) et exige souvent pour leur dépôt soit une synthèse à haute température (> 400 ° C) soit des procédés sous vide. Pour ces raisons, la recherche au cours des dernières années a mis l'accent sur la recherche de TCM alternatifs afin de remplacer l'ITO. Cette thèse s'ancre sur une double approche combinant simulations numériques et des expériences pour explorer le dépôt et l'optimisation des réseaux de nanofils d'argent pour une utilisation comme électrode transparente d'une part et d'améliorer la compréhension de leurs propriétés physiques d'autre part. L'approche par simulation concerne la modélisation de la percolation de réseaux de nanofils 2D tandis que la composante expérimentale explore les propriétés électriques et optiques des réseaux de nanofils d'argent et notamment le comportement de la résistance électrique lors de recuits thermiques. Nous présentons dans ce travail la modélisation 2D de la percolation de systèmes initialement composés de bâtonnets parfaits au sein d'un réseau idéal, puis l'étude de l'influence de paramètres tels que: la distribution des longueurs de bâtonnets, des distributions angulaires ou de la courbure de ces bâtonnets. Nous nous sommes aussi intéressés à la divergence de la densité critique nécessaire pour observer la percolation au sein de systèmes de petite taille (vis-à-vis de la longueur des bâtonnets). Par ailleurs un travail préliminaire sur la simulation de l'efficacité de collecte (ou d'injection) de charges par un réseau de nanofils est présenté. Le volet expérimental fournit une analyse de l'influence de la longueur des fils, de leur diamètre, de la densité du réseau et enfin de la méthode de dépôt sur les propriétés optiques et électriques des réseaux de nanofils d'argent. Une étude approfondie de l'effet de recuit thermique sur les propriétés des réseaux a été réalisée qui a révélé plusieurs mécanismes qui sont à l'origine de la diminution initiale de la résistance électrique à relativement basse température puis la divergence de la résistance électrique observée à haute température. Une observation originale a permis de révéler un phénomène de percolation géométrique quantifiée pour les réseaux peu denses qui a été associé à la présence de chemins efficaces de percolation indépendants. Ce travail permet de conclure que les réseaux de nanofils d'argent constituent une solution intéressante pour une utilisation comme électrode transparente en remplacement de l'ITO ; notamment car ils ont des propriétés mécaniques supérieures et peuvent atteindre des propriétés électro-optiques comparables voire même supérieures. / The use of transparent conductive materials (TCMs) has rapidly increased in the last two decades as a result of increasing demand for personal electronic devices and the development of thin film based solar cells. To date the most commonly used TCM is indium tin oxide (ITO), however indium is a rare earth metal with a complex geopolitical environment surrounding its supply and production. Furthermore the oxide family suffers from poor mechanical properties such as brittleness and generally requires either high temperature synthesis (>400°C) or vacuum processes for their deposition. For these reasons, research in recent years has focused on searching for a TCM to replace ITO. This thesis uses a dual approach combining simulations and experiments to explore the fabrication and optimisation of silver nanowire networks for use as a TCM and to improve the understanding of their physical properties. The simulation component focuses on the application of percolation modelling to 2D nanowire networks while the experimental component explores the electrical and optical properties of silver nanowire networks and their electrical behaviour under thermal annealing. We present in this work the modelling of 2D stick percolation systems initially composed of perfect idealised sticks, and then investigate the influence of parameters such as: length distributions, angular distributions or curved nanowires. We address the divergence of the critical density for the onset of percolation observed for small system sizes and introduce some preliminary work on simulating the collection (or injection) efficiency of charges by a nanowire network. The experimental component provides a discussion of the impact of wire length, wire diameter, network density and fabrication technique on the optical and electrical properties of silver nanowire networks. An in-depth study of the effect of thermal annealing on the networks properties was undertaken which revealed several mechanisms that were responsible for the initial reduction of resistance and final loss of conductivity observed. An original observation enables the revelation of geometrical quantized percolation for rather sparse networks. Finally we conclude that silver nanowire networks are an excellent prospect for a TCM to replace ITO, they have superior mechanical properties and can achieve comparable and even superior electro optical properties.