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8 Jun 2009

Volume 94, Issue 23, Articles (23xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 94, 233101 (2009); http://dx.doi.org/10.1063/1.3148782 (3 pages)

E. Moyen, M. Macé, G. Agnus, A. Fleurence, T. Maroutian, F. Houzé, A. Stupakiewicz, L. Masson, B. Bartenlian, W. Wulfhekel, P. Beauvillain, and M. Hanbücken
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Nonradiative energy transfer in ZnO nanorods/dye-doped polymer heterostructures

Jun Kue Park, Kyu Won Lee, W. Lee, and Cheol Eui Lee

Appl. Phys. Lett. 94, 233301 (2009); http://dx.doi.org/10.1063/1.3153117 (3 pages) | Cited 3 times

Online Publication Date: 9 June 2009

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Nonradiative energy transfer from the ZnO nanorods (donor) to fluorescent dye-doped polymer (acceptor) was investigated in heterostructures of ZnO nanorods/dye-doped polymer films, with the fluorescent dye, 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran, being doped into the host material, poly(9-vinylcarbazole). Introduction of the ZnO nanorods layer to the dye-doped polymer film devices turned out to give much enhanced and blueshifted photoluminescence.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
61.72.U- Doping and impurity implantation
78.66.Qn Polymers; organic compounds
78.66.Hf II-VI semiconductors
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
68.55.ag Semiconductors
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Electronic, magnetic, and physical structure of cobalt deposited on aluminum tris(8-hydroxy quinoline)

Weihao Xu, Jonathan Brauer, Greg Szulczewski, M. Sky Driver, and A. N. Caruso

Appl. Phys. Lett. 94, 233302 (2009); http://dx.doi.org/10.1063/1.3148665 (3 pages) | Cited 15 times

Online Publication Date: 9 June 2009

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X-ray and ultraviolet photoemission of Co deposited onto aluminum tris(8-hydroxyquinoline) (Alq3) is investigated in situ. The initial Co deposited onto Alq3 reacts to form a complex. After 1 nm of Co is deposited core level and valence band spectra show evidence for the formation of metallic cobalt. After 2 nm of Co is deposited onto Alq3 x-ray magnetic circular dichroism spectra reveals the Co is ferromagnetic at 300 K. Transmission electron microscopy images show an abrupt interface between Co and Alq3 with minimal intermixing. These results provide valuable insight into the electronic, magnetic, and physical structure of the Co/Alq3 interface.
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79.60.Jv Interfaces; heterostructures; nanostructures
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
73.20.At Surface states, band structure, electron density of states
75.50.Cc Other ferromagnetic metals and alloys
68.37.Og High-resolution transmission electron microscopy (HRTEM)
78.70.-g Interactions of particles and radiation with matter
78.20.Ls Magneto-optical effects
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Substrate-dependent interface composition and charge transport in films for organic photovoltaics

David S. Germack, Calvin K. Chan, Behrang H. Hamadani, Lee J. Richter, Daniel A. Fischer, David J. Gundlach, and Dean M. DeLongchamp

Appl. Phys. Lett. 94, 233303 (2009); http://dx.doi.org/10.1063/1.3149706 (3 pages) | Cited 78 times

Online Publication Date: 9 June 2009

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The buried interface composition of polymer-fullerene blends is found by near-edge x-ray absorption fine structure spectroscopy to depend on the surface energy of the substrate upon which they are cast. The interface composition determines the type of charge transport measured with thin film transistors. These results have implications for organic photovoltaics device design and the use of transistors to evaluate bulk mobility in blends.
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78.70.Dm X-ray absorption spectra
68.35.Md Surface thermodynamics, surface energies
73.61.Ph Polymers; organic compounds
73.50.Dn Low-field transport and mobility; piezoresistance
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High efficiency organic photovoltaic cells based on a vapor deposited squaraine donor

Siyi Wang, Elizabeth I. Mayo, M. Dolores Perez, Laurent Griffe, Guodan Wei, Peter I. Djurovich, Stephen R. Forrest, and Mark E. Thompson

Appl. Phys. Lett. 94, 233304 (2009); http://dx.doi.org/10.1063/1.3152011 (3 pages) | Cited 24 times

Online Publication Date: 9 June 2009

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2,4-bis[4-(N,N-diisobutylamino)-2,6-dihydroxyphenyl] squaraine (SQ) is used as a donor material in vapor deposited organic heterojunction photovoltaic cells. Devices with the structure indium tin oxide/SQ (x)/C60 (400 Å)/bathocuproine (100 Å)/Al (1000 Å), where x = 65, 110, 150, and 200 Å were compared. Devices with x = 65 Å exhibited a power conversion efficiency of 3.1% under 1 sun, AM1.5G simulated solar irradiation, giving an open circuit voltage of 0.76±0.01 V, a short circuit current of 7.01±0.05 mA/cm2, and a fill factor of 0.56±0.05. Thicker SQ films lead to lower short circuit currents and fill factors, giving conversion efficiencies in the range of 2.6% to 3.2%. The demonstration of sublimable SQ as a donor material opens up a family of compounds for use in small molecule based heterojunction photovoltaics.
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84.60.Jt Photoelectric conversion
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Reliable thin film encapsulation for organic light emitting diodes grown by low-temperature atomic layer deposition

J. Meyer, D. Schneidenbach, T. Winkler, S. Hamwi, T. Weimann, P. Hinze, S. Ammermann, H.-H. Johannes, T. Riedl, and W. Kowalsky

Appl. Phys. Lett. 94, 233305 (2009); http://dx.doi.org/10.1063/1.3153123 (3 pages) | Cited 18 times

Online Publication Date: 9 June 2009

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We report on highly efficient gas diffusion barriers for organic light emitting diodes (OLEDs). Nanolaminate (NL) structures composed of alternating Al2O3 and ZrO2 sublayers grown by atomic layer deposition at 80 °C are used to realize long-term stable OLED devices. While the brightness of phosphorescent p-i-n OLEDs sealed by a single Al2O3 layer drops to 85% of the initial luminance of 1000 cd/m2 after 1000 h of continuous operation, OLEDs encapsulated with the NL retain more than 95% of their brightness. An extrapolated device lifetime substantially in excess of 10 000 h can be achieved, clearly proving the suitability of the NLs as highly dense and reliable thin film encapsulation of sensitive organic electronic devices.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.aj Insulators
78.55.Hx Other solid inorganic materials
66.30.H- Self-diffusion and ionic conduction in nonmetals
85.60.Jb Light-emitting devices
61.46.-w Structure of nanoscale materials
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Realization of high efficiency microcavity top-emitting organic light-emitting diodes with highly saturated colors and negligible angular dependence

Qiang Wang, Zhaoqi Deng, and Dongge Ma

Appl. Phys. Lett. 94, 233306 (2009); http://dx.doi.org/10.1063/1.3153140 (3 pages) | Cited 7 times

Online Publication Date: 10 June 2009

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An alternative way to optimize the emission characteristics of a microcavity top-emitting organic light-emitting diode (TOLED) based on a simple device structure is demonstrated via combining a comprehensive theoretical analysis in the microcavity effects with the experimental modification in the carrier injection of both electrodes. It can be seen that the resulting TOLED exhibits much higher efficiencies and a more saturated color than those of the corresponding conventional bottom-emitting device, as well as hardly detectable color shift with viewing angles. Such a strategy may be more feasible in practical application for active-matrix organic light-emitting diode displays.
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85.60.Jb Light-emitting devices
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Electrical stability of inkjet-patterned organic complementary inverters measured in ambient conditions

Tse Nga Ng (吳子雅), Sanjiv Sambandan, Rene Lujan, Ana Claudia Arias, Christopher R. Newman, He Yan (颜河), and Antonio Facchetti

Appl. Phys. Lett. 94, 233307 (2009); http://dx.doi.org/10.1063/1.3153510 (3 pages) | Cited 28 times

Online Publication Date: 10 June 2009

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Complementary organic inverters were fabricated by inkjet patterning of both the metal contacts and the semiconductors. Bottom-gate, bottom-contact organic thin-film transistors with Ta2O5-polymer bilayer dielectrics, inkjet-printed silver electrodes, and inkjet-printed organic semiconductors exhibit hole and electron mobilities as high as ∼ 10−2 cm2/V s. Complementary inverters based on these transistors operate in ambient and exhibit a gain of −4.4 with supply voltage VDD = +20 V and −3 dB cutoff at 100 kHz with a load of 0.02 pF. The electrical stability of the inverters was evaluated for analog and digital operation, and a noise margin ≥ 1.1 V at VDD = +15 V was measured with bias-stress effects included.
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85.30.Tv Field effect devices
72.20.Fr Low-field transport and mobility; piezoresistance
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Peculiarities of holes injection into organic molecular solids

N. S. Averkiev, V. A. Zakrevskii, I. V. Rozhansky, and N. T. Sudar

Appl. Phys. Lett. 94, 233308 (2009); http://dx.doi.org/10.1063/1.3147858 (3 pages) | Cited 1 time

Online Publication Date: 11 June 2009

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A microscopic mechanism of holes injection from metallic electrode into organic molecular solids (OMSs) in high electric field is proposed. A case is considered of ionization energy of the molecules exceeding work function of the metal. It is shown that the main contribution to the injection current comes from direct isoenergetic transitions (without interaction with phonons) from localized states in OMS to empty states in the metal. Strong dependence of the injection current on applied voltage originates from variation of the number of empty states available in the metal rather than by modification of the interface barrier shape.
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73.30.+y Surface double layers, Schottky barriers, and work functions
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
72.20.-i Conductivity phenomena in semiconductors and insulators
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Effects of semiconducting and metallic single-walled carbon nanotubes on performance of bulk heterojunction organic solar cells

Liming Liu, William E. Stanchina, and Guangyong Li

Appl. Phys. Lett. 94, 233309 (2009); http://dx.doi.org/10.1063/1.3153514 (3 pages) | Cited 11 times

Online Publication Date: 11 June 2009

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This letter reports that the performance of organic solar cells made from blended films of regioregular poly 3-hexylthiophene and methanofullerene can be boosted by introducing single-walled carbon nanotubes (SWCNTs) into the active layer at low concentration. However, the performance degrades at higher SWCNTs concentration. The intensity dependent photocurrent measurement shows that the decreased performance at higher concentration of SWCNTs is attributed to bimolecular recombination in the presence of metallic SWCNTs. Meanwhile, it has been found that the increased performance at low concentration of SWCNTs is due to the increased carrier mobility as semiconducting SWCNTs provide lower resistance pathways.
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84.60.Jt Photoelectric conversion
72.40.+w Photoconduction and photovoltaic effects
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