Kippelen, Bernard

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Now showing 1 - 10 of 12
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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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    Tailoring the work function of indium tin oxide electrodes in electrophosphorescent organic light-emitting diodes
    (Georgia Institute of Technology, 2009) Sharma, Asha ; Hotchkiss, Peter J. ; Marder, Seth R. ; Kippelen, Bernard
    We investigate the use of organic surface modifiers based on phosphonic acid anchoring groups that react with the surface of indium tin oxide (ITO) in order to modify its work function, surface energy, and the charge injection in organic multilayer electrophosphorescent devices. The phosphonic acid surface modifiers, possessing different substituting groups, are found to tune the work function of ITO in the range of 4.40–5.40 eV. These surface modifiers have been tested as an interfacial layer between the ITO anode and hole transport layers HTL that are either processed from the vapor phase or from solution. The use of this interfacial layer with a solution-processible HTL results in high quantum and luminous efficiencies of 20.6% and 68 cd/A at 100 cd/m² (17.5% and 60 cd/A at 1000 cd/m²). The enhanced performance of the devices incorporating phosphonic acid modifiers could be associated with an improved charge injection and a better compatibility with the hydrophobic nature of the organic layer. The performance of these devices is also compared to that of devices in which ITO is modified with other well-known techniques such as air plasma treatment or the use of a layer of poly (3,4-ethylenedioxythiophene)/poly (styrenesulfonate).
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    Effect of phosphonic acid surface modifiers on the work function of indium tin oxide and on the charge injection barrier into organic single-layer diodes
    (Georgia Institute of Technology, 2009) Sharma, Asha ; Haldi, Andreas ; Hotchkiss, Peter J. ; Marder, Seth R. ; Kippelen, Bernard
    We investigate the use of several phosphonic acid surface modifiers in order to increase the indium tin oxide (ITO) work function in the range of 4.90–5.40 eV. Single-layer diodes consisting of ITO/modifier/N,N′-diphenyl-N,N′-bis(1-naphthyl)-1,1′ biphenyl-4,4″ diamine (α-NPD)/Al and ITO/modifier/pentacene/Al were fabricated to see the influence of the modified ITO substrates with different work functions on the charge injection. To calculate the charge injection barrier with different surface modifiers, the experimentally measured current density-voltage (J-V) characteristics at different temperatures are fitted using an equivalent circuit model that assumes thermionic emission across the barrier between the ITO work function and the highest occupied molecular orbital of the organic material. The charge injection barrier height extracted from the model for various surface modifier-based diodes is independent of the ITO work function within the range of changes achieved through modifiers for both α-NPD and pentacene-based single-layer diodes.
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    Stabilization of the work function of indium tin oxide using organic surface modifiers in organic light-emitting diodes
    (Georgia Institute of Technology, 2008-10) Sharma, Asha ; Kippelen, Bernard ; Hotchkiss, Peter J. ; Marder, Seth R.
    We herein report on the performance and improved stability of organic light-emitting diodes (OLEDs) in which the transparent indium tin oxide (ITO) electrode is modified using organic surface modifiers based on phosphonic acid anchoring groups. In contrast to air plasma treatment, a commonly used technique to increase the work function of ITO, treatment of the ITO surface with a partially fluorinated phosphonic acid results in a comparable change in work function but with a higher stability over time. The resultant lifetime of OLEDs also increased when this phosphonic acid modified ITO was used.
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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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    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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    Direct imaging through scattering media by use of efficient third-harmonic generation in organic materials
    (Georgia Institute of Technology, 2004-11) Ramos-Ortiz, Gabriel ; Cha, Myoungsik ; Kippelen, Bernard ; Walker, Gregory A. ; Barlow, Stephen ; Marder, Seth R.
    We report on real-time, time-gated, direct imaging through scattering media with an attenuation of 14 mean-free paths by use of third-harmonic generation in the eye-safe and telecommunication-compatible near-IR spectral region (1550 nm).
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    Photorefractive polymer composite operating at the optical communication wavelength of 1550 nm
    (Georgia Institute of Technology, 2004-11) Tay, Savaş ; Thomas, Jayan ; Eralp, Muhsin ; Li, Guoqiang ; Kippelen, Bernard ; Marder, Seth R. ; Meredith, Gerald ; Schülzgen, Axel ; Peyghambarian, Nasser
    A photorefractive polymer composite sensitized at 1550 nm through direct two-photon absorption has been developed. We show an external diffraction efficiency of 3% in four-wave-mixing experiments and perform holographic reconstruction of distorted images utilizing thin-film devices made of this polymer composite. Amongst other potential applications, the demonstration of accurate, dynamic aberration correction through holography in this all-organic photorefractive device presents an alternative to complex adaptive optics systems currently employed in through-air optical communication links.
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    Ultrafast-pulse diagnostic using third-order frequency-resolved optical gating in organic films
    (Georgia Institute of Technology, 2004-10) Ramos-Ortiz, Gabriel ; Cha, Myoungsik ; Thayumanavan, S. ; Mendez, J. C. ; Marder, Seth R. ; Kippelen, Bernard
    We report on the diagnostic of ultrafast pulses by frequency-resolved optical gating (FROG) based on strong third-harmonic generation (THG) in amorphous organic thin films. The high THG conversion efficiency of these films allows for the characterization of sub-nanojoule short pulses emitting at telecommunication wavelengths using a low cost portable fiber spectrometer.
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    Video-rate compatible photorefractive polymers with stable dynamic properties under continuous operation
    (Georgia Institute of Technology, 2004-09) Fuentes-Hernandez, Canek ; Thomas, Jayan ; Termine, Roberto ; Meredith, Gerald ; Peyghambarian, Nasser ; Kippelen, Bernard ; Barlow, Stephen ; Walker, Gregory A. ; Marder, Seth R. ; Yamamoto, Michiharu ; Cammack, Kevin ; Matsumoto, Kenji
    We report on photorefractive polymer composites that exhibit stable dynamic properties under continuous operation. These materials are based on a bis-triarylamine side-chain polymer matrix with a low ionization potential. The evolution of the response time for exposures up to 4 kJ∕cm² was studied and compared with that obtained in poly(n-vinylcarbazole) (PVK) based composites. In the composites, operational stability is combined with video-rate compatible dynamics, large dynamic range at moderate fields, and long shelf lifetimes.