A new growth process for crystalline ultra-thin layers of conjugated oligomers used in field-effect transistor applications

Most organic semiconductor materials dewet on silicon wafers with thermal oxide layers. While Si-wafers represent convenient substrates for building a field effect transistor (FET), dewetting largely destroys the possibility for obtaining a compact and continuous crystalline thin organic semiconductor film and thus limits the mobility in these systems. Using oligothiophenes, we present an approach where the initial dewetting process can be turned into an advantage for generating very thin but large crystalline domains of a size up to the millimetres with all molecules sharing a single orientation. Our approach can be easily extended to other molecules, which have strongly differing growth velocities in the various directions of the crystal, for example due to directional π-stacking interactions. FETs devices based on such large crystalline domains showed charge carrier mobilities that were two orders of magnitude higher compared to non-crystallized films

Study of charge transport in low band-gap semiconducting polymers and its impact on phototovoltaic performances

Le transport de charges dans une série de copolymères à faible bande interdite basés sur l'alternance de motifs riches en électrons (thiophène, thiénothiophène) et d‘unités déficients en électrons (benzothiadiazole) et dans leurs mélanges avec un dérivé du fullerène (PCBM-C60) a été étudié. Les polymères sont différenciés par la structure moléculaire de leur coeur conjugué et par la nature, la position et la densité de leurs chaines latérales. Dans les polymères purs, la mobilité a été étudiée en fonction de la densité de charges par le biais de l’analyses de caractéristiques électriques de transistors à effet de champ et de dispositifs à un seul type de porteurs dont le courant est limité par la charge d’espace. En utilisant le modèle de transport de charges développé par Vissenberg et al., nous avons pu estimer le degré de désordre dans le film organique et corréler le transport de charge avec le degré d’ordre structural mesuré par la diffraction des Rayons-X. Ces polymères ont été conçus pour être utilisés dans la couche active des cellules solaires organiques. Grâce à l’étude du transport de charges dans les mélanges à différents ratios massiques polymères:fullerène, nous avons mis en évidence l’effet considérable de la structure moléculaire sur le ratio optimal polymère:fullerène. Aussi, nous avons pu montrer que la nature des chaînes latérales joue un rôle important dans l’obtention d’un chemin de percolation optimal à la conduction des électrons.The charge transport in a series of low band-gap copolymers based on the alternation of electron-rich units (thiophene, thienothiophene) and electron-deficient units (benzothiadiazole) and in their blends with a fullerene derivative (PCBM-C60) is investigated. The polymers are differentiated by the molecular structure of the conjugated backbone and by the nature, position and density of alkyl side chains. In pristine polymer films, the hole mobility has been investigated as a function of charge carrier density by analyzing the electrical response of field-effect transistors and single carrier spacecharge- limited current devices. By using the charge transport model developed by Vissenberg et al., we could quantify the structural disorder for the different polymers and correlate their degree of anisotropy with structural data obtained by Grazing Incidence Wide Angle X-ray diffraction. These polymers have been used in the active layer of organic solar cells. The ambipolar chargetransport was investigated in the corresponding polymer:fullerene blends. The results show that the side chains play a major role on the polymer: fullerene interactions and controls the optimal weight ratio. Also, we have shown that the nature of the side chains has a strong impact in the optimal electron conducting pathways

Etude du transport de charges dans les polymères semi-conducteurs à faible bande interdite et de son impact sur les performances photovoltaïques

The charge transport in a series of low band-gap copolymers based on the alternation of electron-rich units (thiophene, thienothiophene) and electron-deficient units (benzothiadiazole) and in their blends with a fullerene derivative (PCBM-C60) is investigated. The polymers are differentiated by the molecular structure of the conjugated backbone and by the nature, position and density of alkyl side chains. In pristine polymer films, the hole mobility has been investigated as a function of charge carrier density by analyzing the electrical response of field-effect transistors and single carrier spacecharge- limited current devices. By using the charge transport model developed by Vissenberg et al., we could quantify the structural disorder for the different polymers and correlate their degree of anisotropy with structural data obtained by Grazing Incidence Wide Angle X-ray diffraction. These polymers have been used in the active layer of organic solar cells. The ambipolar chargetransport was investigated in the corresponding polymer:fullerene blends. The results show that the side chains play a major role on the polymer: fullerene interactions and controls the optimal weight ratio. Also, we have shown that the nature of the side chains has a strong impact in the optimal electron conducting pathways.Le transport de charges dans une série de copolymères à faible bande interdite basés sur l'alternance de motifs riches en électrons (thiophène, thiénothiophène) et d‘unités déficients en électrons (benzothiadiazole) et dans leurs mélanges avec un dérivé du fullerène (PCBM-C60) a été étudié. Les polymères sont différenciés par la structure moléculaire de leur coeur conjugué et par la nature, la position et la densité de leurs chaines latérales. Dans les polymères purs, la mobilité a été étudiée en fonction de la densité de charges par le biais de l’analyses de caractéristiques électriques de transistors à effet de champ et de dispositifs à un seul type de porteurs dont le courant est limité par la charge d’espace. En utilisant le modèle de transport de charges développé par Vissenberg et al., nous avons pu estimer le degré de désordre dans le film organique et corréler le transport de charge avec le degré d’ordre structural mesuré par la diffraction des Rayons-X. Ces polymères ont été conçus pour être utilisés dans la couche active des cellules solaires organiques. Grâce à l’étude du transport de charges dans les mélanges à différents ratios massiques polymères:fullerène, nous avons mis en évidence l’effet considérable de la structure moléculaire sur le ratio optimal polymère:fullerène. Aussi, nous avons pu montrer que la nature des chaînes latérales joue un rôle important dans l’obtention d’un chemin de percolation optimal à la conduction des électrons

Novel low bandgap phenothiazine functionalized DPP derivatives prepared by direct heteroarylation: Application in bulk heterojunction organic solar cells

The synthesis by direct heteroarylation of three novel low bandgap donor-acceptor-donor molecules is reported herein. The molecules are based on three different diketopyrrolo-pyrrole (DPP) electron deficient cores, functionalized with different electron rich heteroarenes, (thiophene, thiazole and thienothiophene) and symmetrically linked to two terminal donor phenothiazine rings. The optical properties of the synthesized dyes have been measured both in solution and as thin film and a focus has been given on the study of optoelectronic properties as a function of the different heteroarenes (thiophene, thiazole or thienothiophene) functionalizing the DPP core. Bandgap values as small as 1.55 eV have been observed. The energy of the Frontier orbitals has been estimated by means of electrochemical characterization. The electronic properties of the reported molecules have been investigated more in details by computational analysis performed at the DFT level. The new dyes were used as donor materials in BHJ solar cells and the photovoltaic characterization of these devices led to a maximum power conversion efficiency of 0.7%

3,6-Dialkylthieno[3,2-b]thiophene moiety as a soluble and electron donating unit preserving the coplanarity of photovoltaic low band gap copolymers

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Mapping quality and parameters of photovoltaic liquid crystal modulators

Photovoltaic light modulators integrate liquid crystals and solar cells and offer an exciting prospect for autonomous, smart displays and visors. Illumination produces a photovoltage that modifies the liquid crystal alignment and light transmission. However, determining their properties, for example, the voltage dropped across the liquid crystal, different pretilts or anchoring energies, inherent to asymmetric cell designs, poses significant challenges. We have successfully applied to such photovoltaic modulators a new measurement methodology based on wide-area cross-polarized intensity measurements, coupled to an Ericksen-Leslie model. We have implemented it in a versatile optical analyzer, driven by a Matlab graphical user interface

Versatile synthesis of alpha-fused BODIPY displaying intense absorption in the NIR region and high electron affinity

International audienceWe report the design and highly efficient and versatile synthesis of four isomers of alpha-fused boron dipyrromethene (BODIPY). Structure-property relationships have been established through photophysical and electrochemical properties analysis as well as first-principles calculations. A comparative study of their charge transport properties has been carried out in Organic Field Effect Transistor (OFET) devices, and this allowed the identification of a high mobility material (10(-2) cm(2) V-1 s(-1)) displaying balanced ambipolar behavior

An Electron-Transporting Thiazole-Based Polymer Synthesized Through Direct (Hetero)Arylation Polymerization

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