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Marder,
Seth R.
Marder,
Seth R.
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ItemTailoring 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, BernardWe 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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ItemEffect 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, BernardWe 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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ItemStabilization 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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ItemSolution-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, XiaohongWe 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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ItemPlanar photonic crystals infiltrated with nanoparticle/polymer composites(Georgia Institute of Technology, 2007-11) Tay, Savaş ; Thomas, Jayan ; Momeni, Babak ; Askari, Murtaza ; Adibi, Ali ; Hotchkiss, Peter J. ; Jones, Simon C. ; Marder, Seth R. ; Norwood, Robert A. ; Peyghambarian, NasserInfiltration of planar two-dimensional silicon photonic crystals with nanocomposites using a simple yet effective melt processing technique is presented. The nanocomposites that were developed by evenly dispersing functionalized TiO₂ nanoparticles into a photoconducting polymer were completely filled into photonic crystals with hole sizes ranging from 90 to 500 nm. The infiltrated devices show tuning of the photonic band gap that is controllable by the adjustment of the nanoparticle loading level. These results may be useful in the development of tunable photonic crystal based devices and hybrid light emitting diodes and solar cells.