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

Detection of volatile organic compounds using organic field effect transistors: Influence of the polarity of both analyte and lateral side chains of the sensing organic semiconductor

National audienc

Detection of volatile organic compounds using organic field effect transistors: Hysteresis of transfer characteristics as an efficient tool for alcohol detection

International audienc

Detection of volatile organic compounds using organic field effect transistors: Hysteresis of transfer characteristics as an efficient tool for alcohol detection

International audienc

Ultra trace detection of explosives in air: development of a portable fluorescent detector.

International audienceThis paper describes a system for the detection of nitroaromatic explosives consisting of a portable detector based on a specific fluorescent material. The developed sensor was able to perform an ultra trace detection of explosives, such as trinitrotoluene (TNT) or its derivate 2,4-dinitrotoluene (DNT), in ambient air or on objects tainted with explosives. In the presence of nitroaromatic vapors, the fluorescence of the material was found to decrease due to the adsorption of nitroaromatic molecules on its specific adsorption sites. The sensor exhibited a large sensitivity to TNT or DNT at their vapor pressures (respectively 6 and 148 ppbv) and the detection threshold was evaluated on a laboratory test setup and was found to be 0.75 ppbv for TNT. Moreover, the detector demonstrated no loss of performance in the presence of humidity or interfering compounds. All the tests led to the conclusion that the sensor fulfills the main requirements for the identification of suspect luggage, forensic analyses or battlefields clearing

Theoretical study of new donor-π-Acceptor compounds based on Carbazole, Thiophene and Benzothiadiazole for photovoltaic application as dye-sensitized solar cells

International audienceIn this study, we have designed a series of novel double organic D-π-A (electron donor-π-conjugated-acceptor) based on Carbazole, Thiophene and Benzothiadiazole. The optimized structures and optoelectronic properties of these dyes have been investigated by using the Density Functional Theory DFT/B3LYP/6-31G (d, p) method and Time Dependant Density Functional Theory (TD/DFT) calculations. These dyes consist of electron-donor (Carbazole-3,4-Ethylenedioxythiophene) and-acceptors/anchoring (Benzothiadiazole and Cyanoacrylic), connected by the π-conjugated linker as an electron donor spacer constituted of Thiophene and Phenylene units. The calculated geometries indicate that these dyes have coplanar structures. The LUMO and HOMO energy levels of these dyes can ensure positive effect on the process of electron injection and dye regeneration. In order to predict the band gaps for guiding the synthesis of novel materials with low band gaps, we apply quantum-chemical techniques to calculate the band gaps in several oligomers. The trend of the calculated HOMO-LUMO (Egap) gaps nicely compares with the spectral optical data. A low band gap will be expected in polymers containing double donor-acceptor (D-A) repeating units. The bridging effect by C=C(CN)2 on the optoelectronic properties of the studied compounds is investigated. The calculated results of these dyes demonstrate that these compounds can be used as potential sensitizers for TiO2 nanocrystalline solar cells

Ageing of thin films used in explosives detection

International audienceThe ageing of fluorescent materials (phenyleneethynylene) has been studied to evaluate there lifetime as chemical sensors and to identify the ageing mechanism

DFT/TD-DFT characterization of conjugational electronic structures and spectral properties of materials based on thieno[3,2-b][1]benzothiophene for organic photovoltaic and solar cell applications

cited By 2International audienceIn this work, a theoretical study on five organic π-conjugated molecules based on thieno[3,2-b][1]benzothiophene using together quantum methods, density functional theory (DFT) and its derivative time dependent-density functional theory (TD-DFT) is reported. Different electron side groups were introduced as a bridge to investigate their effects on the electronic structure; The HOMO, LUMO, chemical hardness (η), chemical potential (μ), electronegativity (χ), electrophilicity power (ω), reorganization energy total (λtotal), open circuit voltage (Voc), the gap energy and NBO analysis of these compounds have been reported and discussed in this paper. Thus, our aim is to explore their electronic and spectroscopic properties on the basis of the DFT quantum chemical calculations, and at the same time, we are interested to make an idea on the parameters influencing the photovoltaic efficiency toward a better understanding of the structure–property relationships. The calculated results of these compounds reveal that C4, C5, with thiophene and thienopyrazine as a bridge group respectively, can be used as a potential donor of electron in organic Bulk Heterojunction solar cells (BHJ), due to its best electronic and optical properties and good photovoltaic parameters. The study of electronic, optical and structural properties of these compounds could help to design more efficient functional photovoltaic organic materials. © 2017 King Saud Universit

Nanocrystalline chromium disilicide synthesized by a fast Chlorine-Transfer-Reaction

International audiencePure nanocrystalline chromium disilicide (CrSi2) were synthesized for the first time by a fast Chlorine-Transfer-Reaction between chromium chloride and silicon with the support of thermodynamics calculation. The use of sodium and lithium chloride diluent enables to decrease the aggregates size from ∼2000 nm to ∼500 nm and to reach a nanocrystallite size ranging from 50 to 200 nm suitable for new application