Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

Organic field-effect transistors (OFET) have attracted considerable interests as a promising technology for the next-generation flexible electronics. Thioacenes have recently emerged as potential semiconducting materials for OFETs. On the other hand, Photovoltaic (PV) technology is regarded as a prospective alternative for green and renewable energy source. Recently, dye sensitized solar cells (DSSCs) have drawn intensive attention and showed great potential for practical application. Herein, the research in this thesis would include the synthesis and characterization of novel thioacene-based semiconductors for OFET and DSSC applications. To begin with, a general review on the current status of organic semiconductors for OFET and DSSC applications was presented in Chapter 1. In chapter 2, a series of novel benzodithieno[3,2-b]thiophene derivatives (BDTT-n) with different lateral alkyloxy groups were designed and synthesized. In addition, alkyloxy-substituted benzo[2,1-b:3,4-b’]bis-[1]benzothiophenes derivatives (BBBT-n) were also synthesized. The performances of OFETs based on BDTT-n and BBBT-n have been fully investigated. Among them, BDTT-4 based OFET exhibited the highest hole mobility of 1.74 cm 2 /(Vs) with a current on/off ratio above 10 7 without annealing. In chapter 3, a novel series of naphthodithiophene-based oligomers with D-A- D-A- D structure motif were designed and synthesized. All these oligomers have 2 been fully characterized by NMR and mass spectrometry. The hole mobility properties of these oligomers were determined in OFETs as fabricated by drop- coating technique. These oligomers exhibited typical p-type semiconducting behavior. A mobility of 1.6x10 -2 cm 2 /(Vs) was demonstrated by ENBT based OFET with a current on/off ratio in the range of 10 5-7 after annealing at 160ºC. Besides, in chapter 4, a novel [pi]-bridge, namely naphthodithienothiophene was developed and employed to explore photosensitizers for DSSC application. In this work, four novel photosensitizers with D-A-[pi]-A or D-[pi]-A structure motif were designed and synthesized in which the carbazole or triphenylamine derivative was used as a donating group and benzothiadiazole was applied as auxiliary accepting group. The performances of DSSCs based on these photosensitizers have been fully investigated. Among them, CB-NDTT- CA based device exhibited the highest power conversion efficiency (PCE) of 7.29%. Meanwhile, the interfacial properties of these photosensitizers anchored on TiO 2 have also been studied by ab-initio simulation and Gaussian calculations. In chapter 5, another novel series of photosensitizers with benzodithienothiophene as the [pi]-bridge would be presented, in which different donors, auxiliary acceptors, and structures were incorporated into the frameworks of D-[pi]-A motif to investigate the relationship between the structure and properties. The performances of DSSCs based on these photosensitizers have been fully investigated, and BD-5 based device exhibited the best power conversion efficiency (PCE) of 4.66%. Furthermore, it was demonstrated that molecular engineering was an efficient way to modulate the performance of the DSSCs in 3 which benzothiadiazole was used as an effective auxiliary accepting group in constructing photosensitizers with D-A-[pi]-A structure motif. The di-anchoring approach was also found to be a promising method to design photosensitizers with improved performance.

Ce travail de thèse porte sur les divers aspects de l'application de la microscopie à force atomique (AFM), pour la caractérisation de semi-conducteurs organiques et de réseaux d’ADN, pour des applications en électronique organique et en biologie. Sur ces surfaces molles, le mode de fonctionnement Amplitude modulation de l’AFM a été choisi. Ce choix est argumenté par une étude des processus dissipatifs, réalisée sur un échantillon particulier, une puce à ADN. Nous avons montré l’influence des paramètres expérimentaux d’amplitude sur la qualité des images topographique et de phase. A partir du calcul de l’énergie dissipative, il a été montré que la dissipation sur la puce ADN était principalement induite par une interaction pointe-échantillon de type viscoélastique. L’étude par AFM de la croissance “thickness-driven“ du pentacène a été réalisée afin de relier sa morphologie à la nature du substrat et aux performances électriques pour la réalisation de transistors organiques à effet de champ, OFET (Organic Field EffectTransistor). Déposé sur deux substrats de polymères, le parylène et le benzocyclobutène (BCB), le pentacène a été caractérisé à l’échelle nanométrique pour des épaisseurs de film entre 6 et 60nm. Il a été démontré que les grains créés par le dépôt étaient les plus étendus pour une épaisseur déposée de 30nm. La spectroscopie AFM en mode contact a été utilisée, comme une alternative à la méthode des angles de contact, pour mesurer localement l'énergie de surface. Une énergie de surface minimale caractéristique d’une surface mieux ordonnée a été mesurée pour l’épaisseur de pentacène déposée de 30nm pour les deux substrats. Des méthodes spectrales d'analyse statistique d’images, à base de PSD (Power Spectrum Density), ont été utilisées pour expliquer la morphologie des films de pentacène. En outre, ces modèles ont fourni une description exhaustive non seulement de la surface accessible de l’échantillon, mais aussi de ses propriétés structurales intérieures. Mise en évidence dans les modèles, cette épaisseur critique de 30nm correspond à une transition de la phase orthorhombique à la phase triclinique pour les molécules de pentacène déposées surparylène. De même, une transition polymorphique se produit sur le BCB. Sur des OFET créés à base de pentacène sur BCB, la mobilité la plus importante de 3.1x10-2cm²/Vs correspond à la couche de pentacène de 30nm, ce qui montre l'avantage de l'moléculaire orthorhombique en comparaison du triclinique. L’assemblage moléculaire de structures en X et en Y à base d’ADN a été observé par AFM à l’air et dans deux solutions buffer de Tris et HEPES sur un substrat de mica. Il a été montré que le traitement du mica par des ions Ni2+ augmente la force d’interaction ADN/substrat et réduit la diffusivité des molécules. A l'air, des macromolécules filaires contenant une seule structure double brin sont observées sur le mica non traité et des macromolécules avec une géométrie 2D ramifiée, sur le mica prétraité. Sur une surface non-traitée, l’agitation thermique suffit à déplacer les molécules d’ADN faiblement liées au mica, ce qui conduit à la formation de structures plus simples 1D. L’organisation est différente dans les solutions de Tris et d’HEPES. Dans la solution deTris, contenant des cations Mg2+, les arrangements conduisent à une architecture 2D, bien organisée. Dans la solution d’HEPES, contenant des cations Ni2+, la force ionique est 10 fois plus faible, qui conduit à une rupture des liaisons préalablement formées entre le mica et l'ADN. Cependant, les molécules d'ADN restent les unes près des autres en raison d'une substitution partielle des cations de Mg2+ déjà adsorbés par les cations de Ni2+ de plus grande affinité avec le mica. [...] / This work reports the various aspects of the application of atomic force microscopy (AFM), for the characterization of organic semiconductors and DNA-based arrays, for organic electronics and biological applications. On these soft surfaces, the amplitude modulation AFM mode was chosen. This choice is argued by a study of dissipative processes, performed on a particular sample, a DNA chip. We showed the influence of experimental parameters on the topographic and phase image quality. By calculating the dissipative energy, it was shown that the dissipation on the DNA chip was mainly induced by a viscoelastic tip-sample interaction.The AFM study of the "thickness-driven” pentacene growth was made to link the morphology to the nature of the substrate and to the electrical performance of created pentacene-based Organic Field Effect Transistor (OFET). Deposited on two polymer substrates, parylene and benzocyclobutene (BCB), pentacene has been characterized for nanoscale film thicknesses between 6 and 60nm. It has been shown that the larger grains were created for a deposited thickness of 30nm. Spectroscopic AFM mode was used as an alternative to the method of contact angles, to measure local surface energy. Decrease of surface energy is characteristic of a more ordered surface and was measured for a thickness of 30 nm of pentacene deposited on both substrates. Models of statistical analysis of spectral images, based on the Power Spectrum Distribution (PSD) have been used to explain the morphology of pentacene films. In addition, these models have provided a comprehensive description not only of the accessible surface of the sample, but also of its internal structural properties. Highlighted in the models, the critical thickness of 30 nm corresponds to a transition from the orthorhombic phase to the triclinic phase for pentacene molecules deposited on parylene. Similarly, a polymorphic transition occurs on the BCB. On OFETs, based on pentacene on BCB, the largest mobility of 3.1x10-2 cm²/Vs corresponds to the pentacene layer of 30nm, that shows a better ordering of the orthorhombic molecular packing in comparison with the triclinic packing.The molecular arrangement of X and Y structures based on DNA was observed, by AFM, in air and in two buffer solutions of Tris and HEPES on a mica substrate. It was shown that the treatment of the mica by Ni2 + ions increases the strength of the DNA/substrate interaction and reduces the diffusivity of the molecules. In air, wired macromolecules containing one double-stranded structure are observed on untreated mica and macromolecules with a 2D geometry on pretreated mica. Onto a non-treated, the greater thermal motion of weakly bounded to mica DNA molecules leads to the rupture of intermolecular bonding and the forming structures are more simple and not branched. The organization is different in solutions of Tris and HEPES. In the Tris solution, containing Mg2+ cations, the arrangement leads to a well-organized 2D architecture. In the HEPES solution, containing Ni2+ cations, the ionic strength is 10 times lower, this leads to a breaking of the bonds previously formed between DNA and mica. However, DNA molecules are near each other due to a partial substitution of already adsorbed Mg2 + cations by Ni 2 + cations of higher affinity with the mica. These results show that the two liquids promote a 2D assembly. In air, the networks are not stable and the few observed ones remain in a dendritic structure on the surface of pretreated mica and as a linear macromolecule on the untreated mica.

Ce travail de thèse porte sur l'étude de dérivés du pérylène-3,4:9,10-tétracarboxylique acide diimide comme semi-conducteurs pour l'électronique organique, et plus particulièrement pour la réalisation de transistors organiques à effet de champs. Les objectifs de ce travail sont la synthèse de dérivés du pérylène à l'aide entre autres de réactions d'halogénation ou de couplage de Suzuki-Miyaura, et la fabrication de transistors organiques à effet de champs. Dans un premier temps, une large gamme de dérivés du pérylène a été synthétisée et caractérisée. Des études spectroscopiques et électrochimiques ont pu être menées, notamment afin de déterminer les énergies des orbitales frontières de nos molécules. Puis dans un second temps, la réalisation de transistors organiques à effet de champs a été mise en oeuvre, en commençant par un gros travail d'optimisation des conditions de formulation des encres, de dépôt et de traitement du film. Puis ces transistors ont été caractérisés en mesurant les courants drain-source. Mots-clés : semi-conducteur, pérylène, transistor organique à effet de champs, couplage de Suzuki-Miyaura, impression jet d'encre. / This study deals with the synthesis of perylene-3,4:9,10-tetracarboxylic acid bisimide derivatives and their use as semi-conductors for organic electronics, and more specifically for the realization of organic field-effect transistors. The goals of this study are the synthesis of perylene derivatives, using halogenation reactions or Suzuki-Miyaura coupling, and the fabrication of organic field-effect transistors.In the first part of the work, a wide variety of perylene derivatives has been obtained and fully characterized. Spectroscopic and electrochemical studies have been performed to determine energy levels of the frontier orbitals.In the second part, the making of organic field-effect transistors was realized, beginning with the research of optimal conditions for ink formulation, deposition and annealing of the film. Then those devices have been characterized by measuring the source-drain current.Keywords: semi-conductor, perylene, organic field-effect transistor, Suzuki-Miyaura coupling, ink jet printing.

Solution-processed organic field effect transistors (OFETs) have emerged in recent years as promising contenders to be part of electronic and optoelectronic circuits owing to their compatibility with low-cost high throughput roll-to-roll manufacturing technology. The stringent performance requirements for OFETs in terms of carrier mobility, switching speed, turn-on voltage and uniformity over large areas require the performance of single crystal-based OFETs, but these suffer from major scale-up challenges. To achieve device performance approaching that of single crystals with scalable, high throughput and industry-compatible solution coating of OFETs requires understanding and ultimately controlling the crystallization of organic semiconductors (OSCs), and producing very low defect-density thin films. In this thesis, we develop an understanding of the process-structure-property-performance relationship in OSCs that bring fresh insights into the nature of solution crystallization and lead to novel ways to control OSC crystallization, and finally help achieve fabrication of high-performance OFETs by scalable, high throughput and industry-compatible blade coating method. We probe the solution crystallization of OSCs by employing a suite of ex & in situ characterization techniques. This leads us to an important finding that OSC molecules aggregate to form a dense amorphous intermediate state and nucleation happens from this intermediate state during blade coating under a wide window of coating conditions. This phenomenon resembles the so-called two-step nucleation model. Two-step nucleation mediates the crystallization of a wide range of natural and synthetic products ranging from soft materials, such as proteins, biominerals, colloids and pharmaceutical molecules, to inorganic compounds. We go on to show that this nucleation mechanism is generally applicable to achieve formation of high-quality polycrystalline films in a variety of small molecule OSCs and their polymer blends. This phenomenon results in highly textured and well-connected domains, which exhibit reduced interfacial and bulk trap-state densities, helping raise the carrier mobility by one to two orders of magnitude in OFETs in comparison to direct nucleation. We extend the understanding developed for solution crystallization of various acenes and thiophene-based small molecule OSCs to the high-performance benzothieno-benzothiophene (BTBT) based small molecule OSCs. On this end, we develop protocols to fabricate high-quality thin films of BTBT based OSCs by blade coating at industrially compatible coating speeds (>100 mms-1). These films show massive single-domains with very few apparent defects when crystallized via multiple liquid-crystalline phases in two-step nucleation conditions, resulting in an average carrier mobility of ~10 cm2V-1s-1. To sum up, this thesis develops an understanding of OSC solution crystallization and efficient protocols to control polycrystalline thin film quality for high-performance OFETs. These protocols involve a combination of two-step nucleation pathway, solvent mixtures, polymer blends and device-manufacturing conditions. Our efforts enable to realize high-performance OFETs based on high-quality polycrystalline OSC thin films at industry-compatible conditions.

Les transistors organiques à effet de champ (OFETs) dans lesquels le transport des charges se fait à travers un film mince de molécules organiques représentent une transformation de la technologie des transistors à effet de champ au regard de la technologie au silicium. Ils permettent notamment d’envisager le développement d’une électronique flexible à bas coût. Ce travail porte sur la synthèse, l’étude et l’utilisation en tant que couche active dans des OFETs de type n de couples d’isomères para- et méta-indacénodithiophènes (para- et méta-IDT) appauvris en électrons inédits. Une introduction aux OFETs de type n est tout d’abord présentée. Elle est suivie par la présentation de la synthèse des dérivés IDT et de l’analyse comparée de leurs propriétés physico-chimiques. La fabrication des OFETs, leur caractérisation et l’optimisation de leur architecture est enfin décrite, leurs performances montrant l’intérêt des IDTs pour les OFETs de type n. Différentes fonctionnalisations menant à des IDTs d’architecture 3π-2spiro sont également synthétisées afin d’étudier les propriétés intrinsèques de ces dérivés π-conjugués et d’envisager leur incorporation comme matrice hôte dans des diodes électrophosphorescentes organiques. / Organic Field Effect Transistors (OFETs), in which the charge transport is carried through a thin film made of organic molecules represent a transformation of the FET technology regarding that based on Silicon. They offer in particular the possibility to manufacture low cost flexible electronics. This work is focused on the synthesis, the study and the use as active layer in n-type OFETs of novel, electron poor, couples of para- and meta-indacenodithiophenes isomers (para- and meta-IDT). First of all, an introduction to the field of n-type OFETs is presented, followed by the presentation of the synthesis of the IDT derivatives and the comparative analysis of their properties. Finally, the fabrication of the OFETs, their characterization and the optimization of their architecture is described. The performances recorded attest that these derivatives are of great interest for the n-type OFETs. Different 3π-2spiro IDT derivatives are also presented in order to study the IDTs intrinsic properties and to envisage their incorporation as host in phosphorescent organic light-emitting diodes.

<p>  </p> <p>Organic semiconductors have been considered a promising candidate to replace Silicon-based inorganic semiconductors in our electronics due to their lightweight, high flexibility, and solution processability. Recently, conjugated polymers were shown to be functional at up to 200°C, expanding organic semiconductors application territory into high-temperature electronics, which sorely depends on wide-bandgap semiconductors. To push the operational temperature boundary of polymer transistors even further than 200°C, our understanding of temperature impacts on the materials and charge transport mechanism in such harsh conditions needs to be improved. Here, we study the high temperature effect on polymer transistors from two main directions: via molecular design and via device engineering. First, via sidechain design, we explored the impact of close π-π packing on the thermal stability of semiconducting polymers. We discovered that maintaining close π-π packing can lead to lower chain distortion, thus improving the polymer transistors' operational stability at high temperatures. Then we study the impact from device factor, specifically contact resistance in device behavior at extreme conditions. We found that the contact area is more susceptible to high temperatures than other regions in the channels and is the main reason for the degraded performance. We then propose a facile method to minimize the contact problem, to achieve stable devices at above 200°C. And last, we proposed a simple method to attain quasi-temperature independent charge transport in polymer transistors from room temperature to 140°C by simply applying a prolonged bias gate voltage before heating. This research expands our knowledge on charge transport in conjugated polymers at high temperatures and provides a guide to make conjugated polymer transistors for extreme conditions in the future.</p>

En dépit d'une amélioration remarquable de la performance des composants électroniques organiques, il y a encore un manque de compréhension théorique rigoureux sur le fonctionnement du composant. Cette thèse est consacrée à la création de modèles pratiques pour composants électroniques organiques à base physique complet, à savoir un modèle compact à base physique. Un modèle compact à base physique d'un élément de circuit est une équation mathématique qui décrit le fonctionnement du composant, et est généralement évaluée par trois critères: si elle est suffisamment simple pour être incorporé dans des simulateurs de circuits, précise pour rendre le résultat des simulateurs utile les concepteurs de circuits et rigoureux pour capturer des phénomènes physiques se produisant dans le composant. Dans ce contexte, les caractéristiques distinctives de l'injection de porteurs de charge et de transport dans les semi-conducteurs organiques sont incorporés dans les modèles avec un effort particulier pour maintenir la simplicité mathématique. L'effet concomitant sur les caractéristiques courant-tension des diodes et des transistors organiques prototypiques sont étudiés. Les méthodes d'extraction des paramètres cohérents aux modèles sont présentés qui permettent la détermination univoque des paramètres de le composant utilisé pour le fonctionnement du composant de modélisation et l'évaluation des performances de le composant et les propriétés des couches minces et des interfaces organiques. Les approches englobent le developement analytique des équations physiques, la simulation numérique à deux dimensions basé sur la méthode des éléments finis et la validation expérimentale. Les modèles compacts originaux et entièrement analytiques et des méthodes d'extraction de paramètres fournissent une compréhension fondamentale sur la façon dont le désordre énergétique dans une couche mince de semi-conducteur organique, décrit par la densité d’etats Gaussienne, affecte les caractéristiques courant-tension observables des composants.Mots-clés : Electronique organique, physique des composants électroniques, modélisation analytique, diodes, transistors à effet de champ, densité d’etats Gaussienne / In spite of a remarkable improvement in the performance of organic electronic devices, there is still a lack of rigorous theoretical understanding on the device operation. This thesis is dedicated to establishing practical models of organic electronic devices with a full physical basis, namely a physically-based compact model. A physically-based compact model of a circuit element is a mathematical equation that describes the device operation, and is generally assessed by three criteria: whether it is sufficiently simple to be incorporated in circuit simulators, accurate to make the outcome of the simulators useful to circuit designers, and rigorous to capture physical phenomena occuring in the device. In this context, distinctive features of charge carrier injection and transport in organic semiconductors are incorporated in the models with a particular effort to maintain mathematical simplicity. The concomitant effect on the current-voltage characteristics of prototypical organic diodes and transistors are studied. Parameter extraction methods consistent to the models are presented which enable unambiguity determination of device parameters used for modeling device operation and assessing device performance and properties of organic thin-films and interfaces. The approaches encompass analytical developement of physical equations, two-dimensional numerical simulation based on finite-element method and experimental validation. The original and fully analytical compact models and parameter extraction methods provide fundamental understanding on how energetic disorder in an organic semiconductor thin-film, described by the Gaussian density of states, affects the observable current-voltage characteristics of the devices.Keywords : Organic electronics, device physics, analytical modeling, diodes, field-effect transistors, Gaussian density-of-states

This master´s thesis deals with possibilities of application of new organic molecular materials for electronic devices. Nowadays it is a very attractive field of research, because of the tendencies in industry to miniaturize, reduce production costs and develop new, eco-friendlier, processes of production. The theoretical part of the thesis provides a short overview of organic materials suitable for smart applications and thin films issues including their characterization. The experimental part is dedicated to means how to prepare thin-film electronic components to silicon wafers for thin films field effect transistors. The obtained results in the last part of thesis are discussed about properties of prepared thin films, in the concrete about the electrical transport properties, in the connection with the condition of preparation.

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