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219 results on '"Geffroy B"'

1. Diffusion of triplet excitons in an operational Organic Light Emitting Diode

Author

Lebental, M., Choukri, H., Chénais, S., Forget, S., Siove, A., Geffroy, B., and Tutis, E.

Subjects
Condensed Matter - Materials Science, Condensed Matter - Other Condensed Matter
Abstract

Measurements of the diffusion length L for triplet excitons in small molecular-weight organic semiconductors are commonly carried out using a technique in which a phosphorescent-doped probe layer is set in the vicinity of a supposed exciton generation zone. However, analyses commonly used to retrieve $L$ ignore microcavity effects that may induce a strong modulation of the emitted light as the position of the exciton probe is shifted. The present paper investigates in detail how this technique may be improved to obtain more accurate results for L. The example of 4,4'-bis(carbazol-9-yl)1,1'-biphenyl (CBP) is taken, for which a triplet diffusion length of L=16 +/- 4 nm (at 3 mA/cm2) is inferred from experiments. The influence of triplet-triplet annihilation, responsible for an apparent decrease of L at high current densities, is theoretically investigated, as well as the 'invasiveness' of the thin probe layer on the exciton distribution. The interplay of microcavity effects and direct recombinations is demonstrated experimentally with the archetypal trilayer structure [N,N'-bis(naphthalen-1-yl)-N,N'-bis(phenyl)]-4,4'-diaminobiphenyl (NPB)/CBP/ 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (named bathocuproine, BCP). It is shown that in this device holes do cross the NPB/CBP junction, without the assistance of electrons and despite the high energetic barrier imposed by the shift between the HOMO levels. The use of the variable-thickness doped layer technique in this case is then discussed. Finally, some guidelines are given for improving the measure of the diffusion length of triplet excitons in operational OLEDs, applicable to virtually any small molecular-weight material., Comment: Accepted for publication in Physical Review B

Published
2009
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7. Author Correction: Adult sex ratios: causes of variation and implications for animal and human societies.

Author

Schacht, R., Beissinger, S.R., Wedekind, C., Jennions, M.D., Geffroy, B., Liker, A., Kappeler, P.M., Weissing, F.J., Kramer, K.L., Hesketh, T., Boissier, J., Uggla, C., Hollingshaus, M., Székely, T., Schacht, R., Beissinger, S.R., Wedekind, C., Jennions, M.D., Geffroy, B., Liker, A., Kappeler, P.M., Weissing, F.J., Kramer, K.L., Hesketh, T., Boissier, J., Uggla, C., Hollingshaus, M., and Székely, T.

Published
2022

8. Electrolytic Capacitors with a Conducting Polymer

Author

Geffroy, B., Tanguy, J., Cardona, Manuel, editor, Fulde, Peter, editor, von Klitzing, Klaus, editor, Queisser, Hans-Joachim, editor, Lotsch, Helmut K. V., editor, Kuzmany, Hans, editor, Mehring, Michael, editor, and Roth, Siegmar, editor

Published
1992
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15. Direct Experimental Evidence of Halide IonicMigration under Bias in CH3NH3Pbl3 et 8722;xClxet8209;BasedPerovskite Solar Cells Using GD-OES Analysis

Author

Gaiaschi, S., Chapon, P., Marronnier, A., Lee, H., Vanel, Jc., Tondelier, D., Bouree, Je., Bonnassieux, Y., Geffroy, B., HORIBA Jobin Yvon SAS [Chili Mazarin], HORIBA Scientific [France], Laboratoire de physique des interfaces et des couches minces [Palaiseau] (LPICM), Centre National de la Recherche Scientifique (CNRS)-École polytechnique (X), and École polytechnique (X)-Centre National de la Recherche Scientifique (CNRS)

Subjects
[PHYS.NUCL]Physics [physics]/Nuclear Theory [nucl-th], [PHYS.NEXP]Physics [physics]/Nuclear Experiment [nucl-ex]
Abstract

International audience; In recent decades, the development oforganicet8722;inorganic hybrid perovskite solar cells (PSCs)has been increasing very quickly due to their high initialefficiency and low-cost process. However, key points suchas crystal growth mechanisms, currentet8722;voltage hysteresis,and instability remain still unexplained or misunderstood.Among several possibilities, ionic migration in PSCs hasbeen suggested to explain the hysteresis effect. However,direct experimental evidence of ionic migration underoperation or measurement conditions of PSCs is stillmissing. This work shows directly the ionic migration ofhalogen components (Iet8722; and Clet8722;) of a CH3NH3PbI3et8722;xClx perovskite film under an applied bias using glow dischargeoptical emission spectrometry (GD-OES). Furthermore, no migration of lead and nitrogen ions is observed on apolarization time scale less than 2 min. The ratio of fixed to mobile iodide ions is deduced from the evolution of the GDOESprofile lines as a function of the applied bias. The average length of iodide and chloride ion migration is deduced fromthe experimental results.

Published
2017

16. Sex‐ and age‐adjusted prevalence estimates of five chronic inflammatory skin diseases in France: results of the « OBJECTIFS PEAU » study

Author

Richard, M.‐A., primary, Corgibet, F., additional, Beylot‐Barry, M., additional, Barbaud, A., additional, Bodemer, C., additional, Chaussade, V., additional, D'Incan, M., additional, Joly, P., additional, Leccia, M.T., additional, Meurant, J.M., additional, Petit, A., additional, Geffroy, B. Roy, additional, Sei, J.F., additional, Taieb, C., additional, Misery, L., additional, and Ezzedine, K., additional

Published
2018
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18. Red-emitting fluorescent organic light emitting diodes with low sensitivity to self-quenching.

Author

Forget, S., Chenais, S., Tondelier, D., Geffroy, B., Gozhyk, I., Lebental, M., and Ishow, E.

Subjects
METAL quenching, LIGHT emitting diodes, FLUORESCENCE, ORGANIC compounds, AMINES
Abstract

Concentration quenching is a major impediment to efficient organic light-emitting devices (OLEDs). We herein report on OLEDs based on a fluorescent amorphous red-emitting starbust triarylamine molecule [4-di(4′-tert-butylbiphenyl-4-yl)amino-4′-dicyanovinylbenzene, named FVIN], exhibiting a very small sensitivity to concentration quenching. OLEDs are fabricated with various doping levels of FVIN into Alq3, and show a remarkably stable external quantum efficiency of 1.5% for doping rates ranging from 5% up to 40%, which strongly relaxes the technological constraints on the doping accuracy. An efficiency of 1% is obtained for a pure undoped active region, along with deep red emission (x=0.6; y=0.35 in the Commission Internationale de l'Energie (CIE) coordinates). A comparison of FVIN with the archetypal 4-dicyanomethylene-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran dye is presented in an identical multilayer OLED structure. [ABSTRACT FROM AUTHOR]

Published
2010
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20. Organic Light Emitting Diodes: materials, device structures and light extraction

Author

Geffroy, B. and Rocha, L.

Subjects
Light-emitting diodes -- Electric properties, Electroluminescent display systems -- Electric properties, Engineering and manufacturing industries
Abstract

Byline: B. Geffroy, L. Rocha Organic Light Emitting Devices (OLEDs) are presented with particular emphasis on materials, device structures and strategies to improve light extraction. For the fabrication of efficient OLEDs, two types of electroluminescent materials are used (small molecules and polymers) with efficiencies and lifetimes which are now acceptable for small size or low content information displays. Two main approaches are described to enhance external efficiency, one is based on direct modification of the species emission and the other on modification of emitted guided modes propagation within the device. The features of the different approaches are evidenced through examples of devices reported in the literature.

Published
2009

23. A Novel isomer of Pyrrolo[3,4-c]pyrrole-1,4-dione as a New Building Block for Polymer Solar Cells

Author

Parravicini, M, Gironda, R, Choi, J, Bonnassieux, Y, Geffroy, B, Miozzo, L, Tondelier, D, Yassar, A, Papagni, A, PARRAVICINI, MATTEO, GIRONDA, RAMONA, MIOZZO, LUCIANO, PAPAGNI, ANTONIO, Geffroy,B, Parravicini, M, Gironda, R, Choi, J, Bonnassieux, Y, Geffroy, B, Miozzo, L, Tondelier, D, Yassar, A, Papagni, A, PARRAVICINI, MATTEO, GIRONDA, RAMONA, MIOZZO, LUCIANO, PAPAGNI, ANTONIO, and Geffroy,B

Published
2012

27. Exploring ecotoxicological fish bioassay for the evaluation of uranium reprotoxicity

Author

Simon, O., Floc'h, E., Geffroy, B., Frelon, S., and Institut de Radioprotection et de Sûreté Nucléaire (IRSN)

Subjects
[SDV]Life Sciences [q-bio]
Abstract

International audience; Although reproduction in fish is known to be sensitive to metal exposure, few ecotoxicological studies have focused on the toxicological effects of metals. Because uranium (U) is naturally present in aquatic ecosystems (0.6-2mg/L), freshwater organisms are subjected to chronic U exposure. Although new standardized assays are currently being developed to mimic realistic exposure conditions, they could be improved by taking into account the contamination that occurs throughout the life cycle of fish. The authors initially evaluated the effect of food (commercial flakes vs pure Spirulina) and ionic composition of the exposure medium on the reproductive performance of Danio rerio. The effects of U exposure on reproduction then were assessed 1) for the F0 adult stage at short exposure times (5 d, 20 d, and 40 d), and 2) for the F0 stage and the F1 generation after 200 d of exposure to control, low (20μg U/L), and moderate (250μg U/L) waterborne levels of U. Reproductive endpoints (reproductive success, fecundity, number of spawns, egg and larvae viability, and hatching) were measured mainly after the first spawn and after 10 d of cumulative spawns. The authors evaluated the plasticity of these endpoints and compared the effect of exposure conditions to identify the most relevant markers of the effect of U exposure on reproductive performance of D. rerio. Environ Toxicol Chem 2014;331817-1824. © 2014 SETAC.

Published
2014
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28. Objectifs peau : une initiative conjointe des dermatologues et de l’industrie au service des patients

Author

Richard, M.-A., primary, Corgibet, F., additional, Beylot-Barry, M., additional, Barbaud, A., additional, Bodemer, C., additional, Chaussade, V., additional, D’Incan, M., additional, Joly, P., additional, Leccia, M.T., additional, Meurant, J.M., additional, Misery, L., additional, Petit, A., additional, Geffroy, B. Roy, additional, Sei, J.F., additional, Taieb, C., additional, and Ezzedine, K., additional

Published
2016
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38. Dermatosurgery: Total Quality Management in a Dermatology Department

Author

Ingen-Housz-Oro, S., primary, Amici, J.M., additional, Roy-Geffroy, B., additional, Ostojic, A., additional, Domergue Than Trong, E., additional, Buffard, V., additional, Lafaye, S., additional, Moreno, J.C., additional, Goldszal, S., additional, Mirkamali, A., additional, Plaquet, J.L., additional, Thuillot, D., additional, Meningaud, J.P., additional, Wolkenstein, P., additional, and Chosidow, O., additional

Published
2012
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46. Aging effects in polypyrrole probed by positron annihilation

Author

Marie-France Barthe, C. Corbel, Laszlo Liszkay, L. Breivik, H. Kauppinen, and Geffroy B

Subjects
Electron density, Materials science, Annihilation, Dopant, Mechanical Engineering, Doping, Metals and Alloys, Electronic structure, Conductivity, Condensed Matter Physics, Polypyrrole, Electronic, Optical and Magnetic Materials, Positron annihilation spectroscopy, chemistry.chemical_compound, chemistry, Mechanics of Materials, Materials Chemistry, Atomic physics
Abstract

Abstact Positron annihilation spectroscopy and conductivity measurements have been used to probe aging-induced changes in parahydroxybenzenesulfonate doped polypyrrole. Polypyrrole was synthesized by a chemical oxidation process and aged in air at 110 °C and 140 °C up to 250 days. Positron annihilation experiments reveal modifications of the electronic structure accompanied by a dramatic loss of conductivity as a function of the aging time and temperature. The electron-positron momentum distribution at the 511 keV annihilation peak exibits a strong shift towards higher momentum annihilation events upon aging. The experimental results are explained in terms of positron trapping in the vicinity of negative dopants whose concentration is reduced after aging.

Published
1999
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