Kippelen, Bernard

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Now showing 1 - 10 of 11
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    Fabrication of a blue M x N pixel organic light-emitting diode video display incorporating a thermally stable emitter
    (Georgia Institute of Technology, 2009-04) Haldi, Andreas ; Kim, Jung B. ; Domercq, Benoit ; Kulkarni, Abhishek P. ; Barlow, Stephen ; Gifford, Angela P. ; Jenekhe, Samson A. ; Marder, Seth R. ; Kippelen, Bernard
    A 7x11 pixel blue OLED display was fabricated using a patterned indium-tin-oxide (ITO) substrate. The fabrication process for an M x N pixel organic light-emitting diode (OLED) video display including an electrical insulating layer and a physical pixel separator layer is presented. An efficient and thermally stable blue fluorescent organic material, 6, 6'-bis((2-p-biphenyl)-4-phenylquinoline) (B2PPQ), was used in combination with an evaporated hole-transport small molecule with a high ionization potential.
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    Solution-processible high-permittivity nanocomposite gate insulators for organic field-effect transistors
    (Georgia Institute of Technology, 2008-07-07) Kim, P. ; Domercq, Benoit ; Jones, Simon C. ; Hotchkiss, Peter J. ; Marder, Seth R. ; Kippelen, Bernard ; Perry, Joseph W. ; Zhang, Xiaohong
    We report on solution-processible high permittivity nanocomposite gate insulators based on BaTiO₃ nanoparticles, surface-modified with a phosphonic acid, in poly(4-vinylphenol) for organic field-effect transistors. The use of surface-modified BaTiO₃ nanoparticles affords high quality nanocomposite thin films at large nanoparticle volume fractions (up to 37 vol %) with a large capacitance density and a low leakage current (10⁻⁸ A/cm²). The fabricated pentacene field-effect transistors using these nanocomposites show a large on/off current ratio (I on/off 10 ⁴- 10 ⁶) due to the high capacitance density and small leakage current of the gate insulator.
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    Transparent organic field-effect transistors with polymeric source and drain electrodes fabricated by inkjet printing
    (Georgia Institute of Technology, 2008-06-16) Zhang, Xiaohong ; Lee, S. M. ; Domercq, Benoit ; Kippelen, Bernard
    Transparent organic field-effect transistors based on pentacene were fabricated on indium tin oxide (ITO)-coated glass using ITO as the gate electrode, Al2O3 grown by atomic layer deposition as the gate insulator, and an inkjet-printed conducting polymer poly(3,4-ethylenedioxythiophene):poly(4-styrenesulphonate) as the source and drain electrodes. The transistors combine an overall high transmittance (84% in the channel and 78% through source/drain electrodes) in the visible region, a field-effect mobility value of 0.3 cm2/V s, a threshold voltage of -0.2 V, a subthreshold slope of 0.9 V/decade, and an on/off current ratio of 105.
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    Highly efficient green phosphorescent organic light-emitting diodes with simplified device geometry
    (Georgia Institute of Technology, 2008-06) Haldi, Andreas ; Domercq, Benoit ; Kippelen, Bernard ; Hreha, R. D. ; Cho, Jian-Yang ; Marder, Seth R.
    We report on the performance of green phosphorescent organic light-emitting diodes based on the well-known host 4,4′-di(carbazol-9-yl)-biphenyl and the green phosphor emitter fac tris(2-phenylpyridinato-N,C²′) iridium. Using a spin-coated hole-injection/transport layer of poly(N-vinyl-carbazole) and a hole-blocking/electron-transport layer of 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline, devices with efficiencies of 21.2% and 72 cd/A at 100 cd/m² were obtained in a simplified device geometry that requires the deposition of only two organic layers from the vapor phase.
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    High-performance and electrically stable C ₆₀ organic field-effect transistors
    (Georgia Institute of Technology, 2007-08) Domercq, Benoit ; Kippelen, Bernard ; Zhang, Xiaohong
    Electron mobility ranging from 2.7 to 5.0 cm²/V s was achieved when treating the gate dielectric with divinyltetramethyldisiloxane bis(benzocyclobutene) and depositing C ₆₀ at room temperature. The transistors combine threshold voltages near zero, low subthreshold slopes (<0.7 V/decade), on/off current ratios larger than 10 ⁶, excellent reproducibility, and good electrical stability under prolonged continuous dc bias stress.
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    Encapsulation of pentacene/C₆₀ organic solar cells with Al₂O₃ deposited by atomic layer deposition
    (Georgia Institute of Technology, 2007-06) Potscavage, William J., Jr. ; Yoo, SeungHyup ; Domercq, Benoit ; Kippelen, Bernard
    Organic solar cells based on pentacene/C₆₀ heterojunctions were encapsulated using a 200-nm-thick film of Al₂O₃ deposited by atomic layer deposition (ALD). Encapsulated devices maintained power conversion efficiency after exposure to ambient atmosphere for over 6000 h, while devices with no encapsulation degraded rapidly after only 10 h of air exposure. In addition, thermal annealing associated with the ALD deposition is shown to improve the open-circuit voltage and power conversion efficiency of the solar cells.
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    Integrated organic photovoltaic modules with a scalable voltage output
    (Georgia Institute of Technology, 2006-12) Yoo, SeungHyup ; Potscavage, William J., Jr. ; Domercq, Benoit ; Kim, Jungbae ; Holt, J. ; Kippelen, Bernard
    Efficient organic photovoltaic modules and cells have been fabricated based on a blend of poly(3-hexylthiophene) (P3HT) and a soluble C₇ ₀ derivative, [6,6]-phenyl C₇ ₁ butyric acid methyl ester (PCBM-70). Power conversion efficiency of P3HT/PCBM-70 cells is estimated at 4.1% for the AM1.5 G condition from the spectra of external quantum efficiency. Integrated photovoltaic modules, in which N- individual P3HT/PCBM-70 cells (N = 1–4) are connected in series, exhibit a short-circuit current /[subscript SC] of 1.4±0.1 mA and an open-circuit voltage V[subscript OC ]of N×0.621 V with a maximum VOC of 2.48 V for N = 4 under simulated solar illumination (AM1.5 G, 85 mW/cm2).
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    Thermal transport properties of thin films of small molecule organic semiconductors
    (Georgia Institute of Technology, 2005-12) Kim, Namsu ; Domercq, Benoit ; Yoo, SeungHyup ; Christensen, Adam ; Kippelen, Bernard ; Graham, Samuel
    A series of harmonic Joule-heating experiments have been employed to determine the thermal conductivities of thin films of pentacene, N,N -diphenyl−N,N -di 3-methylphenyl − 1,1 -biphenyl -4,4 -diamine, and tris 8-hydroquinolinato aluminum, three widely used organic semiconductors. Room-temperature thermal conductivity values of 0.51, 0.24, and 0.48 W/mK were measured for films of these three compounds, respectively. These values are over two orders of magnitude lower than those of inorganic semiconductors. While amorphous films were found to display only small thermal conductivity changes over the temperature range of 228–350 K, pentacene exhibited stronger variations that are typical of phonon-phonon scattering observed in polycrystalline semiconductors.
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    Intensity-dependent equivalent circuit parameters of organic solar cells based on pentacene and C-60
    (Georgia Institute of Technology, 2005-05) Yoo, SeungHyup ; Domercq, Benoit ; Kippelen, Bernard
    We present studies of the current–voltage characteristics of organic solar cells based on heterojunctions of pentacene and C60 as a function of illumination intensity. The photovoltaic response at a given illumination level is parameterized and modeled using the equivalent circuit model developed for inorganic pn-junction solar cells. Reduction in shunt resistance and increase in diode reverse saturation current density are observed upon increase of the light intensity. We demonstrate that this effect can be modeled by a refined equivalent circuit model that contains an additional shunt resistance and an additional diode the properties of which are functions of the light intensity. The effects of these additional components on the overall photovoltaic performance are discussed.
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    Efficient thin-film organic solar cells based on pentacene/C-60 heterojunctions
    (Georgia Institute of Technology, 2004-11) Yoo, SeungHyup ; Domercq, Benoit ; Kippelen, Bernard
    We have fabricated an efficient organic photovoltaic cell based on a heterojunction of pentacene and C ₆₀. Photocurrent action spectra exhibit broad light-harvesting throughout the visible spectrum with a peak external quantum efficiency (EQE) of 58±4% at short-circuit condition. Modeling studies indicate that this high EQE can be partly attributed to the large exciton diffusion length in the pentacene film as well as efficient dissociation of excitons at the pentacene/ C ₆₀ heterojunction.