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23 Nov 2009

Volume 95, Issue 21, Articles (21xxxx)

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Appl. Phys. Lett. 95, 213501 (2009); http://dx.doi.org/10.1063/1.3265958 (3 pages)

S. Cibella, M. Ortolani, R. Leoni, G. Torrioli, L. Mahler, Ji-Hua Xu, A. Tredicucci, H. E. Beere, and D. A. Ritchie
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Patterned electrode vertical field effect transistor fabricated using block copolymer nanotemplates

Ariel J. Ben-Sasson, Eran Avnon, Elina Ploshnik, Oded Globerman, Roy Shenhar, Gitti L. Frey, and Nir Tessler

Appl. Phys. Lett. 95, 213301 (2009); http://dx.doi.org/10.1063/1.3266855 (3 pages) | Cited 10 times

Online Publication Date: 23 November 2009

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We report the design and implementation of a vertical organic field effect transistor which is compatible with standard device fabrication technology and is well described by a self consistent device model. The active semiconductor is a film of C60 molecules, and the device operation is based on the architecture of the nanopatterned source electrode. The relatively high resolution fabrication process and maintaining the low-cost and simplicity associated with organic electronics, necessitates unconventional fabrication techniques such as soft lithography. Block copolymer self-assembled nanotemplates enable the production of conductive, gridlike metal electrode. The devices reported here exhibit On/Off ratio of 104.
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85.30.Tv Field effect devices
81.16.Nd Micro- and nanolithography
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C60 cluster formation at interfaces with pentacene thin-film phases

B. R. Conrad, J. Tosado, G. Dutton, D. B. Dougherty, W. Jin, T. Bonnen, A. Schuldenfrei, W. G. Cullen, E. D. Williams, J. E. Reutt-Robey, and S. W. Robey

Appl. Phys. Lett. 95, 213302 (2009); http://dx.doi.org/10.1063/1.3266857 (3 pages) | Cited 5 times

Online Publication Date: 24 November 2009

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The C60-thin film pentacene interface was investigated using scanning tunneling microscopy, atomic force microscopy, and ultraviolet photoemission spectroscopy. C60 deposition on a multilayer pentacene film (standing) yields an interface dominated by C60 clusters, regardless of the underlying substrate. Three-dimensional cluster growth dominates due to weak interactions with the underlying Pn. C60 cluster size and density on sequential Pn layers suggest an Ehrlich–Schwoebel-type barrier at Pn layer boundaries. Cluster formation reduces the C60 lowest unoccupied molecular orbital–Pn highest occupied molecular orbital (HOMO) separation, while increasing the respective HOMO-HOMO offset. Heterostructure fabrication protocols can alter interface morphology and induce band shifts on the order of 0.3 eV.
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36.40.-c Atomic and molecular clusters
71.20.Rv Polymers and organic compounds
61.46.Bc Structure of clusters (e.g., metcars; not fragments of crystals; free or loosely aggregated or loosely attached to a substrate)
81.05.Fb Organic semiconductors
07.79.Cz Scanning tunneling microscopes
07.79.Lh Atomic force microscopes
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Solution-processed conjugated polymer organic p-i-n light-emitting diodes with high built-in potential by solution- and solid-state doping

Sankaran Sivaramakrishnan, Mi Zhou, Aravind C. Kumar, Zhi-Li Chen, Rui-Qi Png, Lay-Lay Chua, and Peter K. H. Ho

Appl. Phys. Lett. 95, 213303 (2009); http://dx.doi.org/10.1063/1.3257979 (3 pages) | Cited 7 times

Online Publication Date: 24 November 2009

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Polymer p-i-n homojunction light-emitting diodes (LEDs) comprising p-doped poly(dioctylfluorene-alt-benzothiadiazole) (F8BT) hole-injection, intrinsic F8BT emitter, and n-doped F8BT electron-injection layers have been demonstrated. A thin F8BT film was photocrosslinked and bulk p-doped by nitronium oxidation, then overcoated with an F8BT layer which was then surface n-doped by contact printing with naphthalenide on an elastomeric stamp. These LEDs exhibit high built-in potential (Vbi = 2.2 V), efficient bipolar injection, and greatly improved external electroluminescence efficiency compared to control devices without the p-i-n structure. A modulated photocurrent technique was used to measure this Vbi, which systematically improves with diode structure.
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85.60.Jb Light-emitting devices
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
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Magnetoelectroluminescence in tris (8-hydroxyquinolato) aluminum-based organic light-emitting diodes doped with fluorescent dyes

P. Chen, Y. L. Lei, Q. L. Song, Y. Zhang, R. Liu, Q. M. Zhang, and Z. H. Xiong

Appl. Phys. Lett. 95, 213304 (2009); http://dx.doi.org/10.1063/1.3266844 (3 pages) | Cited 9 times

Online Publication Date: 25 November 2009

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The influences of fluorescent dye doping on the magnetoelectroluminescence in tris (8-hydroxyquinolato) aluminum (Alq3)-based organic light-emitting diodes have been investigated systematically by varying the dopant concentrations and its energy band gap. Our results show that the decrease in electroluminescence intensity at high magnetic field, which survives only at low temperatures for pure Alq3-based devices, persists in dye-doped devices even at room temperature. This is explained here as the result of magnetic field dependent triplet-triplet annihilation process, in which the triplet excitons trapped on the dye molecules play the most important role.
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85.60.Jb Light-emitting devices
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Highly efficient yellow organic light emitting diode based on a layer-cross faded emission layer allowing easy color tuning

Florian Lindla, Manuel Boesing, Christoph Zimmermann, Frank Jessen, Philipp van Gemmern, Dietrich Bertram, Dietmar Keiper, Nico Meyer, Michael Heuken, Holger Kalisch, and Rolf H. Jansen

Appl. Phys. Lett. 95, 213305 (2009); http://dx.doi.org/10.1063/1.3266849 (3 pages) | Cited 12 times

Online Publication Date: 25 November 2009

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An easy way to adjust the color of yellow organic light emitting diodes (OLED) is realized by basing the emission layer on a cross-fading zone of two unipolar-conducting host materials doping parts of it either with a red or green phosphorescent emitter at varying thickness ratios. At color coordinates of 0.47/0.50, a current efficacy of 42.2 cd/A (16.2% external quantum efficiency) and a power efficacy of 32.9 lm/W (1000 cd/m2) are measured without light extraction enhancement. Mixed-host emission layer OLED without cross-fading are processed for comparison. Exciton distributions are studied. The concept is suggested to be useful for white OLED.
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85.60.Jb Light-emitting devices
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Efficient semitransparent small-molecule organic solar cells

Jan Meiss, Karl Leo, Moritz K. Riede, Christian Uhrich, Wolf-Michael Gnehr, Stefan Sonntag, and Martin Pfeiffer

Appl. Phys. Lett. 95, 213306 (2009); http://dx.doi.org/10.1063/1.3268784 (3 pages) | Cited 13 times

Online Publication Date: 25 November 2009

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We present semitransparent small-molecule organic solar cells (OSC) deposited by thermal evaporation onto indium tin oxide (ITO)-coated glass substrates. The devices employ ITO-free ultrathin metal layers as top electrodes, containing 1 nm metal surfactant interlayer for improved morphology. Using a bulk heterojunction of zinc phthalocyanine and C60, sandwiched in between doped dedicated transport layers for efficient charge carrier extraction, power conversion efficiencies comparable to conventional OSC with an intransparent thick back electrode and similar device layout are achieved: the semitransparent OSC yield power conversion efficiencies well above 2% with external quantum efficiencies above 30%–40%. Organic light incoupling layers improve the transmission to up to 50% in the visible part of the optical spectrum.
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88.40.jr Organic photovoltaics
81.15.Dj E-beam and hot filament evaporation deposition
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
78.40.-q Absorption and reflection spectra: visible and ultraviolet
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Enhancement of electrical property by oxygen doping to copper phthalocyanine in inverted top emitting organic light emitting diodes

Kihyon Hong, Kisoo Kim, and Jong-Lam Lee

Appl. Phys. Lett. 95, 213307 (2009); http://dx.doi.org/10.1063/1.3266856 (3 pages) | Cited 12 times

Online Publication Date: 25 November 2009

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We reported the evidence of oxygen doping to copper-phthalocyanine (CuPc) by O2-plasma treatment to inverted top-emitting organic light-emitting diodes (ITOLEDs). In situ synchrotron-radiation photoelectron spectroscopy results showed that a new Cu–O bond appeared and the energy difference between the highest-occupied molecular orbital and EF is lowered by 0.15 eV after plasma treatment. The oxygen ions chemically interacted with Cu atoms and transferred charges to the CuPc. Thus the hole injection barrier was lowered, enhancing the electroluminescent property of ITOLEDs.
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85.60.Jb Light-emitting devices
85.40.Ry Impurity doping, diffusion and ion implantation technology
41.60.Ap Synchrotron radiation
78.60.Fi Electroluminescence
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Increasing organic vertical carrier mobility for the application of high speed bilayered organic photodetector

Wu-Wei Tsai, Yu-Chiang Chao, En-Chen Chen, Hsiao-Wen Zan, Hsin-Fei Meng, and Chain-Shu Hsu

Appl. Phys. Lett. 95, 213308 (2009); http://dx.doi.org/10.1063/1.3263144 (3 pages) | Cited 4 times

Online Publication Date: 25 November 2009

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The direct influence of the vertical carrier mobility on the frequency response of bilayered organic photodiodes (PDs) is investigated for the first time. With fullerene as the acceptor material, changing vertical hole mobility from 2.3×10−5 to 2.8×10−4 cm2/V s increases PD bandwidth from 10 to 80 MHz under a 4 V operation. The influence of deposition rate on vertical hole mobility of pentacene film is also discussed. Our results facilitate the application of bilayered organic PDs on the detection of very-high-frequency optical signals.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.60.Dw Photodiodes; phototransistors; photoresistors
73.50.Dn Low-field transport and mobility; piezoresistance
73.61.Ph Polymers; organic compounds
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