Le présent travail a porté sur l’élaboration d’électrodes à base de polymère conducteur et d’un tapis de nanotubes de carbone alignés pour les applications de supercondensateur.Dans la première partie de ce travail, nous avons porté notre attention sur le choix de nos matériaux et nous avons pu déterminer leur comportement électrochimique en milieu liquide ionique. Les deux polymères choisis : le poly(3-méthylthiophène) et le poly(3,4-diméthylthiophène) possèdent des propriétés très différentes en terme de capacitance, de potentiel d’oxydation, de résistance ou de cyclabilité. Afin d’allier ces propriétés entre elles, nous avons réalisé la synthèse de copolymères obtenus par voie électrochimique en milieu liquide ionique aprotique. Cette électro-co-polymérisation nous a permis d’obtenir une large gamme de matériaux aux propriétés variables selon la composition du polymère.Dans la deuxième partie de ce travail, nous avons optimisé la synthèse électrochimique d’un nanocomposite poly(3-méthylthiophène)/nanotubes de carbone alignés en milieu liquide ionique. Les matériaux obtenus offrent la propriété d’être « auto-supportés » et permettent ainsi de s’affranchir de collecteur de courant. La nanostructuration grâce aux nanotubes et l’absence de collecteur de courant nous ont permis d’améliorer d’un facteur 3 la capacitance spécifique de nos électrodes. Une optimisation des conditions d’élaboration des nanocomposites permettent d’atteindre une capacitance de 180F.g-1 dans EMITFSI à 30°C. / The present work concerned the elaboration of electrodes containing electronic conducting polymer and a carpet of aligned carbon nanotubes for supercapacitor applications. In the first part of this work, we put our attention on the choice of our materials and we were able to determine their electrochemical behavior in ionic liquid. Both chosen polymers : poly(3-méthylthiopène) and poly(3.4-diméthylthiophène) possess very diffrent properties in term of capacitance, oxidation potential, resistance or cyclability. In the second part of this work, we optimized the electrochemical synthesis of a nanocomposite poly(3-méthyltiophène)/aligned carbon nanotubes in ionic liquid. The obtained materials offer the property to be "self-supported" and allow using themselves without current collector. And optimization of the conditions of nanocomposites elaboration allows reaching a capacitance of 180 F.g-1 in EMITFSI in 30°C.

Understanding the fundamentals of Organic semiconductors is crucial aspect towards the technological applications. Conjugated polymers have shown many interesting physical properties. Especially the electronic and optical properties of these materials have great impact on the daily life. Much work has been devoted to gain the knowledge on the electrical and photo physical properties of these materials. Despite the large number of studies in fabrication and characterisation on these devices some of the fundamental properties like charge transport, carrier generation and its control by doping are not well accomplished. The Thesis consists of 6 chapters. First chapter is a brief introduction on various properties of semiconducting polymers. Different charge transport models and their basic mechanisms are discussed. Chapter 2 discusses the synthesis, device making and experimental methods used to characterise the polymer devices. Chapter 3 is focused on transport properties in polypyrrole devices and its variation with different experimental conditions. Chapter 4 is aimed to understand the anomalies in the current-voltage characteristics appearing in some of the thiophene based devices. In Chapter 5, the impedance measurement technique is used to characterise the poly (3-hexylthiophene) devices and the outcomes are presented and chapter 6 summarises all the experimental results obtained in this thesis work and presents some future aspects and directions. Chapter 1: Some of the basic properties and recent advancements in the field of organic semiconductors are discussed in this chapter. Organic semiconductor devices based on conjugated polymers are now becoming alternatives to inorganic semiconductors in many fields. Mobility of these conjugated polymers can be increased by adding dopants and also by choosing appropriate metal contacts for charge injection and extraction. The complexity of the metal-polymer interfaces can be better understood by varying the carrier density and studying their transport properties with various experimental tools. Chapter 2: The polymer films prepared in this study are electrochemically deposited on to various conducting substrates. The doping and de-doping of the carriers is done by passing a current and reversing its polarity for different time intervals. Device structures for the measurements are obtained by making a top contact on top of the polymer layer. The current-voltage (I-V) and impedance measurements are carried out in metal-polymer-metal geometry. Temperature dependent studies down to 10 K were performed in a continuous flow cryostat to understand the role of temperature in transport studies. Impedance and light measurements are also carried out in the same geometry. Chapter 3: Transport measurements on polypyrrole devices have shown a space-charge limited (SCLC) conduction, which is also known as bulk property of the materials. I-V curves displayed non-ohmic behaviour at higher voltages and by varying the carrier density the devices show a transition from trap controlled SCLC to trap free/trap filled SCLC. Traps distribution and energies are estimated from the temperature dependent I-V measurements. Poole-Frenkel behaviour, i.e. field dependent mobility is observed in all the polypyrrole samples. The zero field mobility follows Arrhenius behaviour at higher temperatures. Also the temperature variation of mobility displays field dependent and field independent regimes in fully doped and lightly de-doped polypyrrole films. A zero-bias anomaly is observed as the field goes to zero value below 50 K, due to coulomb-blockade transport. Capacitance measurements have shown pseudo inductive behaviour at higher bias, which is also connected with trap-filling regime of PPy devices. Chapter 4: Current-Voltage anomalies are observed in polythiophene (PTh) and poly (3-methylthiophene) [P3MeT] based devices. The origin of this anomaly is not straight forward in polymer devices, so we investigated it in detail. We propose this is a property specific to the above two materials from various experimental studies. The anomalous behaviour appears when the bias is swept from negative to positive keeping the substrate deposited with polymer as anode. The magnitude of peak to valley current ratio (PVCR) which characterises the merit of device can be varied more than two orders of magnitude by varying the carrier density and as well as by varying scan rate. Since the trap states are also one of the reasons for the origin of this anomaly the rate of filling of these states can be helpful in tuning the magnitude of PVCR. Photo generated carriers in the above devices also help in tuning and controlling the magnitude of anomaly, which can make this device as a suitable candidate for opto-electronic studies. Different conductive substrates such as indium tin oxide, platinum, gold and stainless steel are used for deposition of the above polymers. Top contacts (gold, silver and aluminium) have been also varied to understand the origin of this anomaly. Anomalies are observed with all these different substrates and different top contacts. Finally impedance measurements have shown an elongated tail in the Cole-Cole plot in the region of NDR. Chapter 5: Impedance measurements on poly (3-hexylthiophene) devices have shown different relaxation mechanism by varying the doping concentration. For moderately doped devices the relaxation mechanism is classical Debye-type, whereas for highly de-doped samples the relaxation time of the carriers is distributed. Charge transport parameters such as contact resistance, mobility and conduction mechanism details can be obtained by identifying and fitting the data to the equivalent circuit model. The relaxation time of the carriers can give rough estimation of mobility and capacitance. The capacitance variation with applied bias gives the nature of conduction mechanism in the devices. If the capacitance variation is unaffected by the applied bias the transport is bulk limited, if it changes significantly the transport can be considered as either contact limited or depletion layer controlled. Current-Voltage measurements also show that Schottky behaviour is present in all the devices. The rectification ratio varies with doping concentration; at one optimum doping concentration the rectification is very high. I-V measurements on P3MeT devices with varying carrier density have shown a transition in the conduction mechanism from SCLC to contact limited. In the devices with less carrier density the contact limited mechanism is dominating at lower bias voltage and as the bias increases the bulk limited transport takes over. This highlights the role of carrier density in the transport mechanism. Chapter 6: The conclusions from all the works presented in the thesis are summarised in this chapter. Some of the future directions works are presented.

Nesta dissertação realizamos a síntese eletroquímica e a caracterização eletroquímica e óptica de polímeros conjugados eletroluminescentes no azul, como o poli(p-fenileno) (PPP) e alguns copolímeros. Filmes de PPP, poli(pirrol) (PPI), poli(3-metiltiofeno) (P3MET) e os copolímeros, copoli(p-fenileno-pirrol) (CPPI) e copoli(p-fenileno-3-metiltiofeno) (CP3MET), foram preparados por voltametria cíciica (VC) e cronoamperometria (CR) em eletrodos de óxido de estanho dopado com índio sobre vidro (ITO) em uma solução não-aquosa de acetonitrila e perclorato de tetrabutilamônio contendo os monômeros a diferentes concentrações. Durante a síntese eletroquímica dos filmes de PPP, PPI, P3MET, CPPI e CP3MET, foi usado CaC12 como agente secante em uma caixa-seca para reduzir a umidade do ar. Um tratamento de secagem permitiu um melhor controle sobre o crescimento dos filmes e a presença de umidade na síntese eletroquímica foi correlacionada as diferentes respostas eletroquímicas dos filmes. Os valores de potencial de ionização (PI) e de afinidade eletrônica (AE) foram calculados através da medida dos potenciais no início das curvas voltamétricas direta e inversa, quando foram obtidos os potenciais de oxidação e redução (Eoxd\' e Ered\'). Os valores de energia de gap eletrônico (EgapE) ara esses filmes foram também obtidos por medidas eletroquímicas. Através dos espectros de absorção no UVVIS, foi possível se calcular a energia de gap óptico (EgapO) para os diferentes filmes poliméricos. / In this work we describe the electrochemical and optical aspects of a series of electrochemically synthesized blue-electroluminescent conjugated polymers. The materials employed here comprised poly(p-phenylene) (PPP), poly(pyrro1e) (PPI), poly(3-methylthiophene) (P3MET), poly(p-pheny1ene-pyrrole) (CPPI) copolymer and poly(p-phenylene3methyIthiophene) (CP3MET) copolymer. The films were electrochemically synthesized and deposited onto indium-tin-oxide covered glass (ITO) electrodes. The latter was carried out using either cyclic voltammetry (VC) or cronoamperometry (CR) in a acetonitrile nonaqueous medium containing tetrabutilammonium perclorate and different concentration of the respective monomers. As a further film quality control, the synthesis was carried out within a glove box containing a CaCI2 salt, which acted as drying agent. The latter procedure allowed us to correlate the amount of moisture present within the glove box with the electrochemical properties of the films. The ionization potential (PI) and the electronic affinity (AE) were calculated using the oxidation and reduction on-set potentials of the films (Eoxd\' e Ered\'). The electronic gap (EgapE)d the optical gap energies were calculated using electrochemical and UV-VIS. spectroscopy respectively.

Conducting and semiconducting polymers, consisting of delocalized π-electrons, have been studied for the past three decades. These materials have shown novel physical properties with interesting applications in batteries, detectors, light emitting diodes, field effect transistors, solar cells, biosensors etc. Nevertheless the charge transport properties are yet to be understood in detail due to the complexity of the system, especially due to the interplay of quasi-one dimensionality (q-1D), disorder, localization and electron-electron interactions(EEI). A combined investigation of both conductivity and spin lattice relaxation time, especially at very low temperatures and high magnetic fields, is really lacking in conducting polymers. In this thesis a set of experiments – dc conductivity, magnetoresistance (MR), Nuclear Magnetic Resonance (NMR) spin lattice relaxation time (T1) measurements, magnetic susceptibility amd ac conductivity have been carried out in conducting polymers. NMR being a local probe it is possible to get the nanoscopic scale charge transport mechanism. Further, this helps to develop a consistent understanding among a wide range of the physical properties in conducting polymers. In this thesis author has reported the results of experiments at ultra low temperature (mk) and ultra high magnetic field which give more insight about the roles of electron-electron interaction(EEI) and disorderin charge transport properties. This thesis describes a detailed study of charge transport and NMR relaxation in three representative conducting polymers namely polypyrrole(PPy)., poly-3-methylthiophene(P3MT) and poly3-hexylthiophene(P3HT). The emphasis is to understand the charge transport phenomena and NMR relaxation, especially at ultra low temperatures (down to 20 mk) and high magnetic field (up to 23.4 T). The NMR T1 relaxation mechanisms are discussed in terms of (i) Korringa relaxation, (ii) relaxation due to spin diffusion to paramagnetic centers (SDPC) amd (iii) reorientation of symmetric groups, depending upon the temperature range.

Nesta dissertação realizamos a síntese eletroquímica e a caracterização eletroquímica e óptica de polímeros conjugados eletroluminescentes no azul, como o poli(p-fenileno) (PPP) e alguns copolímeros. Filmes de PPP, poli(pirrol) (PPI), poli(3-metiltiofeno) (P3MET) e os copolímeros, copoli(p-fenileno-pirrol) (CPPI) e copoli(p-fenileno-3-metiltiofeno) (CP3MET), foram preparados por voltametria cíciica (VC) e cronoamperometria (CR) em eletrodos de óxido de estanho dopado com índio sobre vidro (ITO) em uma solução não-aquosa de acetonitrila e perclorato de tetrabutilamônio contendo os monômeros a diferentes concentrações. Durante a síntese eletroquímica dos filmes de PPP, PPI, P3MET, CPPI e CP3MET, foi usado CaC12 como agente secante em uma caixa-seca para reduzir a umidade do ar. Um tratamento de secagem permitiu um melhor controle sobre o crescimento dos filmes e a presença de umidade na síntese eletroquímica foi correlacionada as diferentes respostas eletroquímicas dos filmes. Os valores de potencial de ionização (PI) e de afinidade eletrônica (AE) foram calculados através da medida dos potenciais no início das curvas voltamétricas direta e inversa, quando foram obtidos os potenciais de oxidação e redução (Eoxd\' e Ered\'). Os valores de energia de gap eletrônico (EgapE) ara esses filmes foram também obtidos por medidas eletroquímicas. Através dos espectros de absorção no UVVIS, foi possível se calcular a energia de gap óptico (EgapO) para os diferentes filmes poliméricos. / In this work we describe the electrochemical and optical aspects of a series of electrochemically synthesized blue-electroluminescent conjugated polymers. The materials employed here comprised poly(p-phenylene) (PPP), poly(pyrro1e) (PPI), poly(3-methylthiophene) (P3MET), poly(p-pheny1ene-pyrrole) (CPPI) copolymer and poly(p-phenylene3methyIthiophene) (CP3MET) copolymer. The films were electrochemically synthesized and deposited onto indium-tin-oxide covered glass (ITO) electrodes. The latter was carried out using either cyclic voltammetry (VC) or cronoamperometry (CR) in a acetonitrile nonaqueous medium containing tetrabutilammonium perclorate and different concentration of the respective monomers. As a further film quality control, the synthesis was carried out within a glove box containing a CaCI2 salt, which acted as drying agent. The latter procedure allowed us to correlate the amount of moisture present within the glove box with the electrochemical properties of the films. The ionization potential (PI) and the electronic affinity (AE) were calculated using the oxidation and reduction on-set potentials of the films (Eoxd\' e Ered\'). The electronic gap (EgapE)d the optical gap energies were calculated using electrochemical and UV-VIS. spectroscopy respectively.