Fonctionnalisation du distyryl-bithiophène (impact sur la structure moléculaire sur les performances électriques des transistors à effet de champ)

La recherche de nouveaux semi-conducteurs organiques de type p et n stables à l air, pour la réalisation de transistors à base de couche mince organique (OTFTs), demeure un enjeu majeure pour le développement de l électronique organique. Récemment, il a été montré au laboratoire que les distyryl-oligothiophènes constituent une nouvelle classe de semi-conducteurs organiques de type p qui conduisent à des OTFTs présentant de très bonnes mobilités des porteurs de charge associées à une stabilité exceptionnelle des performances électriques à l air au cours du temps. Au cours de ce travail de thèse plusieurs voies de synthèse ont été développées afin de fonctionnaliser le distyryl-bithiophène (DS2T) avec différents groupements fonctionnels dans le but d évaluer leurs impacts sur les propriétés électriques des OTFTs. Après, un premier chapitre qui rappelle brièvement l enjeu économique lié au développement des transistors basés sur les semi-conducteurs organiques et les différents points clés à résoudre, le second chapitre est consacré à la fonctionnalisation du DS2T par des groupements électro-attracteurs du type perfluoroalkyle ou cyano afin d obtenir des semi-conducteurs de type n. Contrairement à ce qui était attendu, le comportement en film mince révèle un caractère soit isolant soit de type p. Outre les résultats expérimentaux, une étude en Density Functional Theory (DFT) visant à mieux comprendre les effets de ces groupements sur le DS2T est décrite. Au cours de la troisième partie, le DS2T a été fonctionnalisé aux extrémités par des chaînes hexyles pour permettre la fabrication des OTFTs par la voie liquide. Les processus de fabrication décrits offrent l avantage d être peu onéreux, tout en tirant parti des propriétés de cristal liquide pour une organisation moléculaire optimale dans la phase solide. Les performances des OTFTs préparés à la tournette, par dépôt par goutte et par jet de matière sont décrites et comparées à celles obtenues pour un OTFT préparé par évaporation sous vide. Enfin au cours de la dernière partie, une stratégie de synthèse a été développée pour rigidifier le coeur bithiophène dans le but d accroître la planéité du semi-conducteur et donc d améliorer l empilement de type p dans la phase solide. Tout ceci affin d accroitre les performances électriques des OTFTs. La structure RX du composé ponté (kite-DS2T) révèle une forme concave totalement inattendue dans la série oligothiophène. Malgré cette forme, a priori pénalisante, une amélioration par un facteur 5 de la mobilité de type p a été obtenue par comparaison au DS2T. Enfin, au cours de la dernière partie de ce chapitre, une première tentative de transformation au niveau moléculaire de ce nouveau semi-conducteur est décrite pour passer d un système de type p à un système de type nThe research of new air stable p- and n-type organic semiconductors that are the basis of organic thin film transistors (OTFTs) are of key interest in the development of improved organic electronics. Recently, our research group has reported on distyryl-oligothiophenes as a novel class of p-type organic semiconductors with high mobilities and an exceptional stability of electrical performances in air over time. During work done for this dissertation, different synthetic routes were developed in order to functionalize the distyryl-bithiophene (DS2T) with different functional groups to evaluate the impact of chemical substitutions on electronic properties in OTFT devices. The first introductory chapter is dedicated to a short overview of the economic challenges in the development of OTFTs and the different key issues that need to be addressed. The second chapter is devoted to the functionalization of DS2T with different electron-withdrawing groups (EWGs) as perfluoroalkyl chains or cyano groups to obtain n-type semiconductors. Contrary to what has been expected, thin films based on such molecules act as insulating layers or p-type channels. In addition to experimental results, a study by Density Functional Theory (DFT) is described in order to evaluate the effects of such EWGs in DS2T. The third chapter explains how DS2T was end-substituted by two alkyl chains for the fabrication of OTFTs by the solution phase. The described process offers reduced costs with the great advantage of liquid crystalline properties needed for an optimum molecular organization in the solid phase. The performances of OTFTs prepared by spin-coating, drop-casting and by ink-jet are described and compared to those obtained with OTFTs prepared by vacuum evaporation. Finally, a new synthetic route was developed to rigidify the bithiophene core in order to increase the planarity of the semiconducting molecule and as a consequence to increase the p-stacking in the solid phase. The main purpose of the strategy was to increase the OTFT performances. The X-Ray structure of the bridged compound (kite-DS2T) revealed a concave structure unexpected in the oligothiophene series. Despite this molecular structure, unfavourable as a first instance, an increase by a factor 5 in the p-type mobility is obtained for kite-DS2T as compared to DS2T. At the end of this chapter a chemical modification of the new kite-DS2T is described as a first alternative to switch the system from p-type to n-type.AIX-MARSEILLE2-BU Sci.Luminy (130552106) / SudocSudocFranceF

A "Kite" Shaped Styryl End-Capped Benzo[2,1-b:3,4-b ']dithiophene with High Electrical Performances in Organic Thin Film Transistors

The bridging of distyryl-bithiophene leads to a kite shape of the conjugated system. This twist is not like twistacenes or twist deformation in α-oligothiophenes but a curvature such as in bowl shaped systems. Initially perceived to be undesirable, this new semiconductor in OTFT devices provides excellent performances in air, μ = 0.1 cm 2 /V.s, I on /I off > 106, S < 4 V/decade, higher by a factor of 5 to the parent unbridged coplanar analogue. Copyright © 2009 American Chemical Society

Insight about electrical properties of low-temperature solution-processed Al-doped ZnO nanoparticle based layers for TFT applications

International audienceAluminium-doped zinc oxide nanoparticles (NPs) with controlled Al doping contents (AZO(X) with x = 0-0.8 at% of Al) were explored as new oxide semiconductor materials to study the impact of doping on both solution and solid states. Polycrystalline AZOX thin films were produced by spin-coating the dispersions following by a thermal post-treatment at low-temperature (80 degrees C or 150 degrees C). The coated AZO(X) films were employed as active layer in thin-film transistors. Morphology and microstructure were studied by scanning electron microscopy and X-ray diffraction. The impact on the device performances (mobility, conductivity, charge carrier density) of Al-doping content together with the solution state was examined. Spin-coated films delivered an electron mobility up to 3 x 10(-2) cm(2)/Vs for the highest Al-doping ratio AZO(0.8). Despite highly different morphologies, extrinsic doping with aluminium significantly increases the conductivity of low temperature solution-processed AZO(X) NPs series based layers by several orders of magnitude from AZO(0) to AZO(0.8). (C) 2016 Elsevier B.V. All rights reserved

Reduction of Charge-Carrier Recombination at ZnO–Polymer Blend Interfaces in PTB7-Based Bulk Heterojunction Solar Cells Using Regular Device Structure: Impact of ZnO Nanoparticle Size and Surfactant

Cathode interfacial layers, also called electron extraction layers (EELs), based on zinc oxide (ZnO) have been studied in polymer-blend solar cells toward optimization of the opto-electric properties. Bulk heterojunction solar cells based on poly­({4,8-bis­[(2-ethylhexyl)­oxy]­benzo­[1,2-<i>b</i>:4,5-b′]­dithiophene-2,6-diyl}­{3-fluoro-2-[(2-ethylhexyl)­carbonyl]­thieno­[3,4-<i>b</i>]­thiophenediyl}) (PTB7) and [6,6]-phenyl-C71-butyric acid methyl ester (PC₇₀BM) were realized in regular structure with all-solution-processed interlayers. A pair of commercially available surfactants, ethanolamine (EA) and ethylene glycol (EG), were used to modify the surface of ZnO nanoparticles (NPs) in alcohol-based dispersion. The influence of ZnO particle size was also studied by preparing dispersions of two NP diameters (6 versus 11 nm). Here, we show that performance improvement can be obtained in polymer solar cells via the use of solution-processed ZnO EELs based on surface-modified nanoparticles. By the optimizing of the ZnO dispersion, surfactant ratio, and the resulting morphology of EELs, PTB7/PC₇₀BM solar cells with a power-conversion efficiency of 8.2% could be obtained using small sized EG-modified ZnO NPs that allow the clear enhancement of the performance of solution-processed photovoltaic devices compared to state-of-the-art ZnO-based cathode layers

Optical properties of dielectric thin films including quantum dots

International audienceDepending on the minimum size of their micro/nano structure, thin films can exhibit very different behaviors and optical properties. From optical waveguides down to artificial anisotropy, through diffractive optics and photonic crystals, the application changes when decreasing the minimum feature size. Rigorous electromagnetic theory can be used to model most of the components but when the size is of a few nanometers, quantum theory has also to be used. These materials including quantum structures are of particular interest for other applications, in particular for solar cells, because of their luminescent and electronic properties. We show that the properties of electrons in multiple quantum wells can be easily modeled with a formalism similar to that used for multilayer waveguides. The effects of different parameters, in particular coupling between wells and well thickness dispersion, on possible discrete energy levels or energy band of electrons and on electron wave functions is given. When such quantum confinement appears the spectral absorption and the extinction coefficient dispersion with wavelength is modified. The dispersion of the real part of the refractive index can then be deduced from the Kramers- Krönig relations. Associated with homogenization theory this approach gives a new model of refractive index for thin films including quantum dots. Absorption spectra of samples composed of ZnO quantum dots in PMMA layers are in preparation are given

Optical properties of dielectric thin films including quantum dots

International audienceDepending on the minimum size of their micro/nanostructure, thin films can exhibit very different behaviors and optical properties. From optical waveguides down to artificial anisotropy, through diffractive optics and photonic crystals, the application changes when decreasing the minimum feature size. Rigorous electromagnetic theory can be used to model most of the components, but, when the size is a few nanometers, quantum theory also has to be used. The materials, including quantum structures, are of particular interest for many applications, in particular for solar cells because of their luminescent and electronic properties. We show that the properties of electrons in periodic and nonperiodic multiple quantum well structures can be easily modeled with a formalism similar to that used for multilayer waveguides. The effects of different parameters, in particular the coupling between wells and well thickness dispersion, on possible discrete energy levels or the energy band of electrons and on electron wave functions are given. When such quantum confinement appears, the spectral absorption and extinction coefficient dispersion with wavelength are modified. The dispersion of the real part of the refractive index can be deduced from the Kramers-Kronig relations. Associated with homogenization theory, this approach gives a new model of the refractive index for thin films including quantum dots. The bandgap of ZnO quantum dots in solution obtained from the absorption spectrum is in good agreement with our calculation

Highly emissive layers based on organic/inorganic nanohybrids using Aggregation Induced Emission effect

International audienceFluorescent nanohybrids, based on p-extended hydroxyoxophosphole ligands grafted onto ZnO nanoparticles, were designed and studied. The restriction of the intramolecular motions of the organic fluorophore, through either aggregates' formation in solution or processing into thin films, forms highly emissive materials due to a strong Aggregation Induced Emission effect. Theoretical calculations and XPS analyses were performed to analyze the interactions between the organic and inorganic counterparts. Preliminary results on the use of these nanohybrids as solution-processed emissive layers in Organic Light Emitting Diodes (OLEDs) illustrate their potential for lighting applications