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Cette thèse a exploré comment, en mélangeant des matériaux avec des propriétés électriques différentes, il est possible de fabriquer des transistors avec des performances accrues. Des transistors organiques à effet de champ basés sur un oligothiophène (DH4T) ont été fabriqués et optimisés jusqu’à ce que les mobilités mesurées fussent supérieures à celles observées dans des films évaporés. Ces résultats ont été obtenus par le contrôle précis des interfaces et de la vitesse d’évaporation. Des polymères de type p ont été mélangés à des polymères de type n. Chaque solution obtenue a été utilisée pour la fabrication de transistors ambipolaires. Les transistors ont été caractérisés et il a été possible de fabriquer des transistors avec des mobilités équilibrées pour chaque paire de polymères. Des transistors à effet de champ basés sur un mélange de P3HT et d’une molécule photochromique (DAE-Me) ont été fabriqués. Le courant a été mesuré pendant et entre les irradiations et il a été démontré qu’une mémoire non-volatile à multiple niveaux peut être fabriquée / This thesis explored how, by blending of materials with different electrical characteristics, it is possible to fabricate transistors with new or improved performances. First, organic field-effect transistors based on a single oligothiophene, DH4T, were fabricated and optimized until the measured mobility was superior to that observed in vacuum deposited films. This was achieved through careful tuning of the interfaces using self-assembled monolayers and by strong control of the solvent- evaporation rate. P-type polymers were blended with an n-type polymer. Each resulting solution was used for the fabrication of ambipolar field-effect transistors. These devices were characterized and it was found that for each pair of p- and n-type polymers, a transistor with balanced mobilities and high Ion/Ioff could be fabricated. Finally field-effect transistors based on a blend of P3HT and a photoswitchable diarylethene (DAE-Me) were fabricated. The current was measured during and between irradiations and it was demonstrated that a non-volatile multilevel memory could be fabricated.

To better understand the physical and electronic properties of donor and acceptor-based structures used in organic electronic applications, a variety of oligothiophene and naphthalene diimide-based small conjugated molecules were designed, synthesized, and characterized. The materials were initially synthesized using oxidative copper-chloride coupling reactions, palladium-catalyzed amination reactions, Friedal-Crafts acylations, Negishi coupling reactions, and Stille coupling reactions. Once isolated, the physical properties of the compounds were characterized through a combination of X-ray crystal structure, thermogravimetric analysis, differential scanning calorimetry, UV-vis. absorption spectroscopy, cyclic voltammetry, and differential pulse voltammetry, along with comparison to quantum-chemical calculations. In some cases, the radical cations or radical anions were generated by chemical oxidation and analyzed by vis-NIR spectroscopy. Furthermore, the electronic properties of the materials were investigated through incorporation as solution-processed active layers in organic field-effect transistors. Multiple examples exhibited hole- and / or electron-transport properties with electron mobility values of up to 1.5 cm²V⁻¹s⁻¹, which is among the highest yet reported for an n-channel OFET based on a solution-processed small molecule.

One of the aim of this study is to prepare conductive polymer nanocomposites of polypropylene to obtain better mechanical and electrical properties. Composite materials based on conductive fillers dispersed within insulating thermoplastic matrices have wide range of application. For this purpose, conductive polymer nanocomposites of polypropylene with nano dimentional conductive fillers like carbon black, carbon nanotube and fullerene were prepared. Their mechanical, electrical and thermal properties were investigated. Polypropylene (PP)/carbon black (CB) composites at different compositions were prepared via melt blending of PP with CB. The effect of CB content on mechanical and electrical properties was studied. Test samples were prepared by injection molding and compression molding techniques. Also, the effect of processing type on mechanical and electrical properties was investigated. Composites become semiconductive with the addition of 2 wt% CB. Polypropylene (PP) / Carbon Nanotube (CNT) and Polypropylene / Fullerene composites were prepared by melt mixing. CNT&rsquo / s and fullerenes were surface functionalized with HNO3 : H2SO4 before composite preparation. The CNT and fullerene content in the composites were varied as 0.5, 1.0, 2.0 and 3.0 % by weight. For the composites which contain surface modified CNT and fullerene four different compatibilizers were used. These were selected as TritonX-100, Poly(ethylene-block-polyethylene glycol), Maleic anhydride grafted Polypropylene and Cetramium Bromide. The effect of surface functionalization and different compatibilizer on mechanical, thermal and electrical properties were investigated. Best value of these properties were observed for the composites which were prepared with maleic anhydride grafted polypropylene and cetramium bromide. Another aim of this study is to built and characterize transistors which have polyethylene as dielectric layers. While doing this, polyethylene layer was deposited on gate electrode using vacuum evaporation system. Fullerene , Pentacene ve Indigo were used as semiconductor layer. Transistors work with low voltage and high on/off ratio were built with Aluminum oxide - PE and PE dielectrics.

Conjugated polymers comprise some of the most promising materials for new technologies such as organic field effect transistors, solar light harvesting technology and sensing devices. In spite of tremendous research initiatives in materials chemistry, the potential to optimize device performance and develop new technologies is remarkable. Understanding relationships between the structure of conjugated polymers and their electronic properties is critical to improving device performance. The design and synthesis of new materials which self-organize into ordered nanostructures creates opportunities to establish relationships between electronic properties and morphology or molecular packing. This thesis details our progress in the development of synthetic routes which provide access to new classes of conjugated polymers that contain dissimilar side chains that segregate or dissimilar conjugated blocks which phase separate, and summarizes our initial attempts to characterize these materials. Poly(1,4-phenylene ethynylene)s (PPEs) have been used in a variety of organic electronic applications, most notably as fluorescent sensors. Using traditional synthetic methods, asymmetrically disubstituted PPEs have irregular placement of side chains on the conjugated backbone. Herein, we establish the first synthetic route to an asymmetrically substituted regioregular PPEs. The initial PPEs in this study have different lengths of alkoxy side chains, and both regioregular and regiorandom analogs are synthesized and characterized for comparison. The design of amphiphilic structures provides additional opportunities for side chains to influence the molecular packing and electronic properties of conjugated polymers. A new class of regioregular, amphiphilic PPEs has been prepared bearing alkoxy and semifluoroalkoxy side chains, which have a tendency to phase separate. Fully conjugated block copolymers can provide access to interesting new morphologies as a result of phase separation of the conjugated blocks. In particular, donor-acceptor block copolymers that phase separate into electron rich and electron poor domains may be advantageous in organic electronic devices such as bulk heterojunction solar cells, of which the performance relies on precise control of the interface between electron donating and accepting materials. The availability of donor-acceptor block copolymers is limited, largely due to the challenges associated with synthesizing these materials. In this thesis, two new synthetic routes to donor-acceptor block copolymers are established. These methods both utilize the catalyst transfer condensation polymerization, which proceeds by a chain growth mechanism. The first example entails the synthesis of a monofunctionalized, telechelic poly(3-alkylthiophene) which can be coupled to electron accepting polymers in a subsequent reaction. The other method describes the first example of a one-pot synthesis of a donor-acceptor diblock copolymer. The methods of synthesis are described, and characterization of the block copolymers is reported.

In this thesis, we investigate spin-dependent transport through ferromagnet-contacted single-walled carbon nanotubes (SWCNTs), in which charge transport shows the Fabry-Perot (FP) interference effect, the Kondo effect and the Coulomb blockade effect at low temperatures. Hysteric magnetoresistance (MR) is observed in all three transport regimes, which can be controlled by both the external magnetic field and the gate voltage. The MR in the FP interference regime can be well understood by a model considering the intrinsic electronic structure of SWCNTs and the quantum interference effect. In the strongly interacting Kondo regime, the Kondo effect is not suppressed by the presence of nearby ferromagnetism. Several observed MR features including the non-splitted zero-bias Kondo peak and positive MR switching can be explained by the strong Kondo effect and weak ferromagnetism in the leads. In the Coulomb blockade regime, several effects that can be associated with the magneto-Coulomb effect have been observed, and isolated spin accumulation and transport through the SWCNT quantum dot have been realized by a four-probe non-local measurements. We also studied charge transport behavior through organic semiconductor pentacene thin film transistors (OTFTs) in the limit of single- or a few molecular layers of pentacene films. The charge transport in these devices can be well explained by the multiple trapping and release model. The structural disorders induced by the physical and chemical causes, such as grain boundaries, interactions with gate insulator, metal contacts and ambient conditions can be responsible for the localized trap states in the ultrathin layer OTFTs, which are further confirmed by the electric force microscopy (EFM) measurements. / text

Les transistors organiques attirent actuellement beaucoup d'attention en raison des avantages uniques par rapport à leur homologue inorganique. En revanche, la compréhension physique du fonctionnement et du transport des porteurs de charge est très limitée. L'objectif de cette thèse est de contribuer à apporter une meilleure compréhension des transistors organiques. Le Chapitre 1 présente les semi-conducteurs organiques : le mécanisme de conduction, les paramètres essentiels, les matériaux typiques etc. Le Chapitre 2 discute des transistors organi-ques en termes de structures, de mécanismes de fonctionnement, de paramètres principaux et des procédés de fabrication. Le Chapitre 3 étudie la caractérisation statique. Après les méthodes classiques, la méthode de la fonc-tion Y est introduite. Subséquemment, des techniques pour extraire les paramètres principaux sont présentées sé-parément. Enfin, les résultats expérimentaux sur nos échantillons sont exposés. Sur la base des données mesurées, les travaux de modélisation sont présentés dans le chapitre 4. Premièrement, une solution de l'équation Poisson est introduite qui donne la distribution de potentiel et donc la distribution de porteurs dans le film organique. Avec la prise en compte des pièges, les résultats obtenus par simulation sont en bon accord avec les données expérimen-tales. A partir de mesures des caractéristiques de courant –tension effectuées à basse température, on propose une procédure d'analyse de la mobilité en utilisant l'intégrale de Kubo-Greenwood. Ensuite, prenant en compte la dis-tribution de porteurs dans le film organique, une solution de l'équation de Poisson est donnée et la mobilité effec-tive est calculée en fonction de la tension de grille et de la température. Le Chapitre 5 est consacré à l'analyse du bruit à basse fréquence. On étudie d'abord le bruit du canal où une domination du bruit provenant des contacts est observée. En conséquence, une méthode TLM pour l'extraction du bruit des contacts est présentée. Ensuite, un procédure d'analyse des sources de bruit dû au contact est aussi proposée. Les résultats de bruit obtenus sur des transistors organiques de différentes origines sont également discutés à la fin. / Organic transistors recently attract much attention because of their unique advantages over the conventional inorganic counterparts. However, the understanding of their operating mechanism and the carrier transport process are still very limited, this thesis is devoted to such a subject. Chapter 1 presents the organic semiconductors regarding carrier transport, parameters, typically applied materials. Chapter 2 describes the issues related to organic transistors: structure, operating mechanism, principal parameters and fabrication technologies. Chapter 3 deals with the static properties characterization. The commonly used methods are firstly presented and then the Y function method is introduced. Afterwards, the characterization methods for principles parameters are separately discussed. The experimental results on our organic transistors are finally described. Chapter 4 focuses on the mod-eling on the basis of the experimental data, regarding DC characteristics modeling with a solution for Poisson's equation, carrier mobility modeling with using Kubo-Greenwood integral as well as a theoretical analysis of OFETs' carrier mobility involving a solution of Poisson's equation. Chapter 5 analyzes the low-frequency noise in organic transistors. One firstly addresses the channel noise sources and then concentrates on the contact noise extraction and contact noise sources diagnosis. The noise measurements on other samples are also presented.

This master´s thesis deals with new perspective organic molecular materials. A theoretical part contains search themed on organic materials for optical and electronic devices with emphasis on diketopyrrolopyrrole derivatives. The aim of the experimental part was preparation of solutions, thin layers and prototypical planar electronic components from chosen diketopyrrolopyrrole derivatives and their optical and electric characterization. Obtained results are interpreted with perspective on application in organic electronic.

Organic field-effect transistors (OFETs) have attracted tremendous attention due to their flexibility, transparency, easy processiblity and low cost of fabrication. High-performance OFETs are required for their potential applications in the organic electronic devices such as flexible display, integrated circuit, and radiofrequency identification tags. One of the major limiting factors in fabricating high-performance OFET is the large interfacial barrier between metal electrodes and OSC which results in low charge injection from the metal electrodes to OSC. In order to overcome the challenge of low charge injection, carbon nanotubes (CNTs) have been suggested as a promising electrode material for organic electronic devices. In this dissertation, we study the effect of carbon nanotube (CNT) density in CNT electrodes on the performance of organic field effect transistor (OFETs). The devices were fabricated by thermal evaporation of pentacene on the Pd/single walled CNT (SWCNT) electrodes where SWCNTs of different density (0-30/um) were aligned on Pd using dielectrophoresis (DEP) and cut via oxygen plasma etching to keep the length of nanotube short compared to the channel length. From the electronic transport measurements of 40 devices, we show that the average saturation mobility of the devices increased from 0.02 for zero SWCNT to 0.06, 0.13 and 0.19 cm2/Vs for low (1-5 /µm), medium (10-15 /µm) and high (25-30 /µm) SWCNT density in the electrodes, respectively. The increase is three, six and nine times for low, medium and high density SWCNTs in the electrode compared to the devices that did not contain any SWCNT. In addition, the current on-off ratio and on-current of the devices are increased up v to 40 times and 20 times with increasing SWCNT density in the electrodes. Our study shows that although a few nanotubes in the electrode can improve the OFET device performance, significant improvement can be achieved by maximizing SWCNT/OSC interfacial area. The improved OFET performance can be explained due to a reduced barrier height of SWCNT/pentacene interface compared to metal/pentacene interface which provides more efficient charge injection pathways with increased SWCNT/pentacene interfacial area.

Organic electronics based on π-conjugated semi-conductor raises new technology, such as organic film transistors, e-paper, and organic photovoltaic cells that can be implemented cost-effectively on large-area applications. Currently, the device performance is limited by low charge carrier mobility. Poly(3-hexylthiophene) (P3HT) and organic field effect transistors (OFET) is used as a model to investigate morphology of the organic film and corresponding electronic properties. In this thesis, processing parameters such as boiling points and solubility are controlled to impact the micro- and macro-morphology of the film to enhance the charge transport of the device. Alternative approach to improve ordering of polymer chains and increase in charge transport without post-treatment of P3HT solution is studied. The addition of high boiling good solvent to the relatively low boiling main solvent forms ordered packing of π-conjugated polymers during the deposition process. We show that addition of 1% of dichlorobenzene (DCB) to the chloroform based P3HT solution was sufficient to improve wetting and molecular structures of the film to increase carrier mobility. Systematic study of solvent-assisted re-annealing technique, which has potential application in OFET encapsulation and fabrication of top-contact OFET, is conducted to improve mobility of OFET, and, to suggest a cost-effective processing condition suitable for industrial application. Three process parameters: boiling point, polarity, and solubility are investigated to further understand the trend of film response to the solvent-assisted technique. We report the high boiling non-polar solvents with relatively high RED values promote highest improvement in molecular packing and formulate crystalline structure of the thin film, which increases the device performance.