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9 Jul 2012

Volume 101, Issue 2, Articles (02xxxx)

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Appl. Phys. Lett. 101, 023101 (2012); http://dx.doi.org/10.1063/1.4731792 (4 pages)

Feng Wang, Ayan Chakrabarty, Fred Minkowski, Kai Sun, and Qi-Huo Wei
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Improving an organic photodiode by incorporating a tunnel barrier between the donor and acceptor layers

I. H. Campbell and B. K. Crone

Appl. Phys. Lett. 101, 023301 (2012); http://dx.doi.org/10.1063/1.4734505 (3 pages) | Cited 2 times

Online Publication Date: 9 July 2012

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We demonstrate increased photocurrent quantum efficiency in a model donor/acceptor (tetracene/C60) photodiode by incorporating an insulating tunnel barrier between the tetracene and C60 layers. Photodiode efficiency results from the interplay of a number of processes which add to or subtract from the overall device efficiency. The positive rates are those of exciton dissociation and charge separation, the negative rates include exciton and charge transfer complex recombination. We show that by introducing a thin insulating layer between the donor and acceptor layers in a photodiode, we can modify the exciton dissociation and charge transfer complex recombination rates and improve device performance.
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85.60.Dw Photodiodes; phototransistors; photoresistors
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Tetrathiofulvalene and tetracyanoquinodimethane crystals: Conducting surface versus interface

T. Mathis, K. Mattenberger, P. Moll, and B. Batlogg

Appl. Phys. Lett. 101, 023302 (2012); http://dx.doi.org/10.1063/1.4731244 (3 pages)

Online Publication Date: 10 July 2012

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When a tetrathiofulvalene (TTF) crystal is placed onto a 7,7,8,8‐tetracyanoquinodimethane (TCNQ) crystal at room temperature, a highly conducting layer is formed. In this study, we explore to what degree this is due to physical contact or transfer by sublimation of one species onto the other crystal. We have performed a variety of time‐dependent surface conductivity measurements, including TTF lamination on TCNQ at room temperature and low temperatures, as well as deposition of TTF molecules from the gas phase. Crystal-to-crystal contact insignificantly modifies material conductivity while TTF sublimation onto TCNQ is shown to dominate electronic modification.
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73.25.+i Surface conductivity and carrier phenomena
68.35.Ct Interface structure and roughness
64.70.Hz Solid-vapor transitions
72.80.Le Polymers; organic compounds (including organic semiconductors)
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Sensitive gas sensor embedded in a vertical polymer space-charge-limited transistor

Hsiao-Wen Zan, Chang-Hung Li, Chih-Kuan Yu, and Hsin-Fei Meng

Appl. Phys. Lett. 101, 023303 (2012); http://dx.doi.org/10.1063/1.4734498 (4 pages) | Cited 1 time

Online Publication Date: 11 July 2012

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We report a very sensitive gas sensor embedded in a vertical polymer space-charge-limited transistor. The oxidizing and reducing gases act as electron dedoping and electron doping agents on the transistor active layer to change the potential distribution in the vertical channel and hence to change the output current density. With a 30-ppb detection limit to ammonia, the sensor can be used for non-invasive breath monitor in point-of-care applications. The integration of a sensitive gas sensor and a low-operation-voltage transistor in one single device also facilitates the development of low-cost and low-power-consumption sensor array.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
85.30.Fg Bulk semiconductor and conductivity oscillation devices (including Hall effect devices, space-charge-limited devices, and Gunn effect devices)
85.30.Tv Field effect devices
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Highly efficient inverted top-emitting green phosphorescent organic light-emitting diodes on glass and flexible substrates

E. Najafabadi, K. A. Knauer, W. Haske, C. Fuentes-Hernandez, and B. Kippelen

Appl. Phys. Lett. 101, 023304 (2012); http://dx.doi.org/10.1063/1.4736573 (4 pages) | Cited 4 times

Online Publication Date: 11 July 2012

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Green phosphorescent inverted top-emitting organic light-emitting diodes with high current efficacy and luminance are demonstrated on glass and polyethersulfone (PES) substrates coated with polyethylene dioxythiophene-polystyrene sulfonate (PEDOT:PSS). The bottom cathode is an aluminum/lithium fluoride bilayer that injects electrons efficiently into an electron transport layer of 1,3,5-tri(m-pyrid-3-yl-phenyl)benzene (TpPyPB). The cathode is found to be highly sensitive to the exposure of trace amounts of O2 and H2O. A high current efficacy of 96.3 cd/A is achieved at a luminance of 1387 cd/m2 when an optical outcoupling layer of N,N′-Di-[(1-naphthyl)-N,N′-diphenyl]-(1,1′-biphenyl)-4,4′-diamine (α-NPD) is deposited on the anode.
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85.60.Jb Light-emitting devices
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Intermolecular hydrogen-bonded organic semiconductors—Quinacridone versus pentacene

Eric Daniel Głowacki, Lucia Leonat, Mihai Irimia-Vladu, Reinhard Schwödiauer, Mujeeb Ullah, Helmut Sitter, Siegfried Bauer, and Niyazi Serdar Sariciftci

Appl. Phys. Lett. 101, 023305 (2012); http://dx.doi.org/10.1063/1.4736579 (4 pages) | Cited 1 time

Online Publication Date: 12 July 2012

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Quinacridone is a five-ring hydrogen-bonded molecule analogous in structure and size to the well-known organic semiconductor pentacene. Unlike pentacene, quinacridone has limited intramolecular π-conjugation and becomes highly colored in the solid state due to strong intermolecular electronic coupling. We found that quinacridone shows a field-effect mobility of 0.1 cm2/V·s, comparable to mobilities of pentacene in similarly prepared devices. Photoinduced charge generation in single-layer quinacridone metal-insulator-metal diodes is more than a hundred times more efficient than in pentacene devices. Photoinduced charge transfer from quinacridone to C60 is not effective, as evidenced by measurements in heterojunctions with C60. Hydrogen-bonded organic solids may provide new avenues for organic semiconductor design.
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85.30.Tv Field effect devices
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Efficient organic light-emitting diodes through up-conversion from triplet to singlet excited states of exciplexes

Kenichi Goushi and Chihaya Adachi

Appl. Phys. Lett. 101, 023306 (2012); http://dx.doi.org/10.1063/1.4737006 (4 pages) | Cited 4 times

Online Publication Date: 12 July 2012

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Enhanced electroluminescence efficiency is achieved in organic light-emitting diodes through delayed fluorescence of the exciplex state formed between 4,4′,4′′-tris[3-methylphenyl(phenyl)amino]-triphenylamine (m-MTDATA) as an electron-donating material and 2,8-bis(diphenylphosphoryl)dibenzo-[b,d]thiophene (PPT) as an electron-accepting material. The devices exhibited maximum external electroluminescence quantum and power efficiencies of 10.0% and 47.0 lm/W, respectively.
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85.60.Jb Light-emitting devices
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