This master thesis work is performed at ABB Corporate Research Center inVästerås. The aim of this study is to investigate Ag:graphene composites as slidingelectrical contacts, suitable for use in e.g. tap-changers. Three different graphenematerials, all produced by a low-cost exfoliation process, are evaluated in this study. The results are compred to an ongoing work on Ag:GO (graphene oxide) composites. This material has shown very good tribological properties, however it hasbeen difficult to handle during sintering processing. The goal of this study is to geteven better tribological, electrical and mechanical properties than Ag:GO, and also todevelop a new powder-metallurgical method to produce the Ag:graphene composites.The study also investigates the influence of graphene flake size and concentration aswell as microstructure of the Ag:graphene composites. This report focuses on aninvestigation of the graphene raw material quality from the suppliers, and friction,wear and resistance analysis of the composites. This is done by using Ramanspectroscopy, SEM with EDS, LOM, tribometer tests and resistivity analysis. Raman and SEM analyses show that none of the supplied LEG materials are ofhigh-quality G (single or bilayer), but rather multi-layer graphene or even graphite.Small amounts of graphene added to Ag gave extremly low friction (μ<0.2 vs. pureAg μ~1.3, 5 N load and 5 cm/s speed). The composite manufacturing process hadcritical steps, which have to be optimized, to obtain low values of friction. Severedegassing of the composites was observed for some sampes, but the samples stillmaintained good friction values. SEM and EDS analyses of 2dfab’s wear track show abuild-up thin carbon-containing tribofilm on the Ag surface. Indicating that G ispresent, and works as a lubricant, creating good tribological properties. The resultsfrom this project may for sure be of importance for future ABB products in specificindustrial applications.

Dans cette thèse, des films à base de graphène ont été étudiés comme alternatives viables dans la fabrication d'électrodes transparentes (TCE). Elle met l'accent sur des couches fines de graphène (FLG), sur l'oxyde de graphène réduit (RGO) et leurs hybrides avec des nanotubes de carbone (NTCs) pour être utilisé comme TCE dans les cellule solaires organiques (OSC). Les FLGs et RGO ont été préparés par des méthodes d'exfoliation mécanique ou en phase liquide assistée par micro-ondes. Ces nanomatériaux dilués dans un solvant liquide ont été déposé en couche mince par aérographe. Des caractérisations de transport de charge ont été obtenues grâce à la méthode des 4 pointes. Ces échantillons ont été caractérisés: leur transparence(UV-Visible), leur morphologie et leur topographique (MEB, MET, AFM) ainsi que le travail de sortie (UPS). Pour obtenir des informations sur la qualité structurelle des échantillons, nous avons utilisés les méthodes de spectroscopie XPS, Raman et la photoluminescence. / Graphene mate rials have been researched as viable alternatives of transparent conductors electrodes (TCEs) in this thesis. Current study focuses on few layer graphene (FLG), reduced graphene oxide (rGO) and their hybrids with carbon nanotubes (CNTs) for TCE applications inorganic solar cells (OSCs). FLGs and rGOs have been prepared by mechanical and microwave-assisted exfoliation methods. This films of these materials have been produced by hot-spray method. Results of charge transport characterizations by four-point probes, transparency (UV-Vis), measurements, along with morphological (SEM, TEM) and topgraphic (AFM) studies of films have been presented. UPS studies were performed to determine for a work-function. XPS,Raman and Photoluminescence studies have been employed to obtain the information about the structural quality of the samples.

La motivation de cette thèse est la production innovante de germes ultra-minces de silicium cristallin. L’utilisation de tels germes dans un procédé de fabrication de cellules solaires permettrait une réduction importante de la consommation de silicium, qui compte déjà pour 60% du coût de production des panneaux solaires de première génération. Dans le cadre de cette thèse, une méthode pionnière de détachement de germes minces a été mise en oeuvre. Dans cette méthode, une contrainte induite mécaniquement est guidée par des défauts étendus induits par l’implantation d’hydrogène. Par cette méthode, le détachement de germes minces d’environ 710nm d’épaisseurs a été obtenu. Le but est ensuite d’utiliser ces germes pour faire croitre du silicium cristallin avec des épaisseurs variables à souhait, soit une technique kerf-free : sans pertes. Cette étude présente ainsi les étapes menant à la mise en oeuvre de ce procédé : en premier lieu, un état de l’art des méthodes de détachement de films ultra-minces existants est réalisé. Celui-ci nous a ainsi guidés vers l’implantation d’hydrogène en tant que méthode viable du guidage de la fracture. Par la suite, différents tentatives de détachement de germes ultra-minces ont été réalisés puis caractérisés, notamment par MEB, MET, AFM et DRX. Dans de bonnes conditions de collage et de croissance de défauts, le détachement de germes ultra-minces de silicium cristallin a été réalisé. Par la suite, la croissance et la cristallisation de couches de silicium amorphe a été réalisée sur les germes détachés. Pour finir, certaines couches détachées ont été utilisées pour la production de cellules solaires prototypes. / The goal of this thesis is to find an innovative way to produce ultra-thin crystalline silicon seeds. The use of such seeds in a solar cell production process could lead to a significant reduction of the silicon consumption, which cost alone is worth 60% of the total cost of a first generation solar panel. Within the context of this PhD thesis, a pioneer seed exfoliation method was implemented. This method use the defects induced by hydrogen implantation to guide a stress-induced spalling process. This method has allowed the exfoliation of 710nm-thick crystalline silicon seeds. These seeds will then be used for the growth of crystalline silicon layers of any desired thickness, hence a totally kerf-free method. This thesis work presents the steps leading to the implementation of this process: firstly, the state of the art of ultra-thin films exfoliation methods is reviewed, which guided us towards the use of hydrogen implantation as a crack guide. Then, different ultra-thin seeds exfoliation processes were tried and characterized, specifically by SEM, TEM, AFM and XRD. In the right conditions of bonding and defects growth, ultra-thin silicon seeds were successfully exfoliated. The growth and crystallization of amorphous silicon layers on these seeds were then studied. Finally, several exfoliated layers were used for the production of prototype solar cells.

Ce travail concerne l'étude des modifications de nanocharges lamellaires synthétiques (α-ZrP) et de leur influence sur les propriétés mécaniques et barrière aux gaz de nanocomposites à matrice élastomère (SBR). Cette étude s'inscrit dans le cadre de l'amélioration de l'étanchéité des pneumatiques. L'une des originalités de ce travail a résidé dans l'introduction des nanocharges hydrophiles par le biais d'une dispersion aqueuse (slurry), dans la matrice SBR hydrophobe. La première phase de ce travail a consisté à entreprendre plusieurs types de modification des nanocharges afin d'étudier les mécanismes d'intercalation et/ou d'exfoliation des ces dernières dans le slurry. Ces différentes familles de charges modifiées ont été utilisées pour réaliser des nanocomposites selon différentes voies de mise en oeuvre : principalement solvant et latex. Nous avons ensuite étudié l'influence, (i) de la nature des intercalants, (ii) des distances interfoliaires initiales des nanocharges et (iii) des procédés de mise en oeuvre des nanocomposites, sur la morphologie et les propriétés finales des matériaux. Cette étude a montré la synergie de ces trois paramètres et mis en évidence l'importance du contrôle des interactions charges modifiées/matrice sur les propriétés de transport de gaz. Parmi l'ensemble des matériaux synthétisés, nous avons pu mettre en avant une formulation, permettant d'atteindre des propriétés mécaniques et barrière intéressantes. Cette formulation, en voie latex, est basée sur l'utilisation de la charge modifiée aminosilane et de l'agent de couplage Si69 / This work concerns the study of the modification of synthetic lamellar nanofillers (α-ZrP) and their influence on mechanical and gas barrier properties of elastomeric nanocomposites (SBR). This study is part of improving the tire tightness. One of the originalities of this work is the introduction of hydrophilic nanofillers through an aqueous dispersion (slurry) in the hydrophobic SBR matrix. The first step of this work was to undertake several types of nanofiller modifications state in order to study their intercalation/exfoliation mechanisms in a slurry. These different families of modified fillers were then used to make nanocomposites with different ways of implementations: mainly solvent and latex ones. The influence of, (i) the nature of the intercalating agent, (ii) the initial nanofiller interlayer distance and (iii) the nanocomposite implementation processes, on the morphology and final properties of materials were studied. The synergy of these three parameters was demonstrated and the importance of controlling the modified filler/matrix interactions on the gas transport and mechanical properties was also proved. Among all the synthesized materials, a formulation was put forward which allowed to achieve interesting mechanical and barrier properties. This formulation, processed by the latex route, is based on the use of aminosilane modified nanofillers and the Si69 coupling agent

This thesis investigates the chemistry of graphene from its basic synthesis to further modulation of its structure, geometry and surface chemical functional groups. A series of wet chemistry and dry chemistry experiments were performed. The wet chemistry includes the diazonium salt functionalization, graphene oxidation and reduction, nanotube unzipping chemistry, graphite intercalation and exfoliation. The dry chemistry includes chemical vapor deposition and solid carbon source synthesis of graphene, the control of domain size and stacking order, graphene hydrogenation and lithographically patterned graphene superlattices. With all these chemical approaches, graphene's electrical and optical properties, solubility in organic solvents, crystallography, and chemical reactivity were carefully investigated and discussed. In addition to the fundamental chemistry of graphene, the bio- and environmental impact of this new material was also taken into consideration and investigated.

It is of great interest to develop and utilize a high surface area material with optimized hydrogen sorption properties. The need for a renewable energy source to replace automobile gasoline has become more critical in the past decade. Hydrogen is a viable fuel source for automobile usage; however, the question of how hydrogen will be safely and efficiently stored still remains. Critical factors for optimum hydrogen storage include ambient conditions and low activation temperature for adsorption and desorption phenomena. In order for optimum hydrogen adsorption to be achieved, the properties of (1) high surface area, (2) optimum hydrogen adsorption energy, and (3) Kubas interactions between metals and hydrogen molecules need to be considered. Fullerenes have recently become more popular with the discovery and mass production of graphene sheets derived from graphite. Graphene is a modified form of graphite that takes the form of sheets with less agglomeration than its respective graphitic form. This form has the potential for high surface area and storage capabilities. Storage of hydrogen at room temperature must be optimized by increasing the surface area and having an adsorption enthalpy between 15 - 20 KJ/mol. Graphene (G) sheets and graphene oxide (GO) sheets have been utilized as a matrix for hydrogen storage. These materials can also be cross-linked with organic spacers in order to form a porous framework of higher surface area. Metal decorating by calcium and platinum of the G/GO matrix has been used to enhance Kubas interactions, adsorption enthalpies, and spillover phenomenon. The use of a polymer matrix has also been implemented. Polyaniline is a novel superconducting polymer with unique electronic properties. Complexes of Polyaniline with graphene and graphene oxide have been investigated for hydrogen storage properties. Graphene and graphene oxide surface modification via metal decoration have been investigated in order to determine the most efficient synthesis and particle size on the G/GO matrix. Characterization by XRD, BET, adsorption enthalpy, PCT, TGA, FT-IR, and TEM/SEM (when applicable) were employed to optimize and compare the materials in the effort to develop a suitable storage material.

In the crystalline Si solar cell industry, there is a push to reduce module cost through a combination of thinner substrates and increased cell efficiency. Achieving solar cells with sub-100 µm substrates cost-effectively is a formidable task because such thin substrates impose stringent handling requirements and thermal budget due to their flexibility, ease of breakage, and low yield. Moreover, as the substrate thickness decreases the surface passivation quality dictates the performance of the cells. Crystalline Si heterojunction (HJ) solar cells based on hydrogenated amorphous silicon (a-Si:H) have attracted significant interest in recent years due to their excellent surface passivation properties, potential for high efficiency, low thermal budget and low cost. HJ cells with ultra-passivated surfaces showing > 700 mV open-circuit voltages (Voc) and > 20% conversion efficiency have been demonstrated. In these cells, it has been identified that high-quality a-Si:H films deposited by a low-damage plasma process is key to achieving such high cell performance. However, the options for low-damage plasma deposition process are limited. The main objectives of this work are to develop a low-plasma damage a-Si:H thin film deposition process based on remote plasma chemical vapor deposition (RPCVD) and to demonstrate high efficiency HJ solar cells on bulk substrates as well as on ultra-thin silicon and germanium substrates obtained by a novel, low-cost semiconductor-on-metal (SOM) technology. This manuscript presents a detailed description of the RPCVD system and the process leading to the realization of high quality a-Si:H thin films and high efficiency HJ solar cells. First, p-type a-Si:H thin films are developed and optimized, then HJ solar cells are subsequently fabricated on bulk and ultra-thin Si and Ge SOM substrates without intrinsic a-Si:H passivation. Single HJ cells on ~ 500 µm bulk Si and ~25 µm ultra-thin substrates exhibited conversion efficiencies of η = 16% (Voc = 615 mV, Jsc = 34 mA/cm2, and FF = 77%) and η = 11.2% (Voc = 605 mV, Jsc = 29.6 mA/cm2, and FF = 62.8%), respectively. The performance of the ~25 µm cell was further improved to η = 13.4% (Voc = 645 mV, Jsc = 31.4 mA/cm2, and FF = 66.2%) by implementing the dual HJ architecture without front side i-layer passivation. For single HJ cells based on Ge substrates, the results were η = 1.78 % (Voc = 148 mV, Jsc = 35.1 mA/cm2, and FF = 1.78%) on ~500 µm bulk Ge, compared to η =5.3% (Voc = 203 mV, Jsc = 44.7 mA/cm2, and FF = 5.28%) on ~ 50 µm Ge SOM substrates. Respectively, the results obtained on ultra-thin SOM substrates are among the highest reported in literature for based on comparable architecture and substrate thickness. In order to achieve improved cell performance, dual HJ cells with i-layer passivation of both surfaces were fabricated. First, optimized RPCVD-based i-layer films were developed by varying the deposition temperature and H2 dilution ratio (R). It was found that excellent surface passivation on planar substrates with as-deposited minority carrier lifetimes > 1 ms is achievable by using deposition temperature of 200 ºC and moderate dilution ratio 0.5 ≤ R ≤ 1, even without the more rigorous RCA pre-cleaning process typically used in literature for achieving comparable results. Subsequently, dual HJ solar cells with i-layer films were demonstrated on planar and textured bulk Si substrates showing improved conversion efficiencies of η = 17.3% (Voc = 664 mV, Jsc = 34.34 mA/cm2 and FF = 76%) and η = 19.4% (Voc = 643 mV, Jsc = 38.99 mA/cm2, and FF = 77.5%), respectively. / text

Surfactant assisted solution exfoliation of expanded graphite by means of sonication was carried out in an attempt to produce non-covalent charge functionality on the surface of graphene for the directed self assembly of graphene films on patterned substrates via electrostatic interactions. This thesis includes the results of experimental research associated with: 1) quantifying the effectiveness of various di-functionalized dithienothiophene surfactant small molecules, 2) further understanding the surface affinity and interaction mechanism between these surfactant molecules and the surface of expanded graphite and graphene and 3) experimentally testing the feasibility of the directed self-assembly of graphene films by means of charge functionalization of graphene by the surfactant molecules adsorbed onto the surface of exfoliated graphene.

Made available in DSpace on 2016-03-15T19:36:49Z (GMT). No. of bitstreams: 0 Previous issue date: 2015-04-17 / The different methods of obtaining two-dimensional materials are being researched intensively, due to their promising physical and chemical properties. Among the methods of obtaining graphene, the liquid phase exfoliation (LPE) of graphite is proving to be a relatively simple and efficient process for the production of flakes of high quality and large scale. It is primarily based on the separation of the layers of graphite in liquids, such as common organic solvents and aqueous surfactant solutions. In this work the exfoliation of graphite was performed in liquid phase by sonication in aqueous suspension in the presence of an industrial reagent. A comparison with suspensions not using the polymeric surfactant indicates that its presence is necessary, because it prevents the re-agglomeration of the layers after sonication, through the multipolar and electrostatic repulsion mechanism. This result coincides with the reports of most recent works on liquid-phase exfoliation of graphite. / Os diferentes métodos de obtenção de materiais bidimensionais estão sendo pesquisados intensamente, devido a suas promissoras propriedades físicas e químicas. Entre os métodos de obtenção de grafeno, a esfoliação em fase líquida (LPE) de grafite está demonstrando ser um processo relativamente simples e eficaz de produção de flocos de alta qualidade e em larga escala. Ela se baseia principalmente na separação das camadas de grafite em líquidos, tais como solventes orgânicos comuns e soluções surfactantes aquosas. Neste trabalho foi realizada a esfoliação de grafite em fase líquida através da sonificação em suspensão aquosa em presença um reagente industrial. A comparação com resultados usando suspensões sem o agente surfactante polimérico indica que a presença deste é necessária, pois evita a reaglomeração das camadas após a sonificação, através do mecanismo de multipolo e repulsão eletrostática. Este resultado coincide com os reportes dos trabalhos mais recentes realizados sobre esfoliação em fase líquida de grafite.

Nowadays, new approaches to fabricate high-performance electrode materials are of vital importance in the renewable energy field. Here, we present a facile synthesis procedure of 3D Ni(OH)2/graphene hybrids for supercapacitors via synchronous electrochemical-assisted exfoliation and assembly of graphene on 3D Ni(OH)2 networks. With the assistance of an electric field, the electrochemically exfoliated high-quality graphene can be readily, uniformly assembled on the surfaces of 3D Ni(OH)2. When serving as electrode materials for supercapacitors, the resulting 3D Ni(OH)2/graphene composites exhibited excellent specific capacitance (263 mF cm−2 at 2 mA cm−2), remarkable rate capability and super-long cycle life (retention of 94.1% even after 10 000 continuous charge–discharge cycles), which may be attributed to their highly porous, stable 3D architecture as well as uniform, firm anchoring of ultrathin graphene on their surfaces. Therefore, our approach provides a facile strategy for the large-scale synthesis of high-quality graphene based composites towards various applications.