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29 Nov 2010

Volume 97, Issue 22, Articles (22xxxx)

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Appl. Phys. Lett. 97, 223101 (2010); http://dx.doi.org/10.1063/1.3519844 (3 pages)

Jin-Kyu Yang, Svetlana V. Boriskina, Heeso Noh, Michael J. Rooks, Glenn S. Solomon, Luca Dal Negro, and Hui Cao
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Liquid crystal-ZnO nanoparticle photovoltaics: Role of nanoparticles in ordering the liquid crystal

L. J. Martínez-Miranda, Kaitlin M. Traister, Iriselies Meléndez-Rodríguez, and Lourdes Salamanca-Riba

Appl. Phys. Lett. 97, 223301 (2010); http://dx.doi.org/10.1063/1.3511736 (3 pages) | Cited 1 time

Online Publication Date: 29 November 2010

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We investigate the role that order plays in the transfer of charges in the ZnO nano-particle-octylcyanobiphenyl (8CB) liquid crystal system, considered for photovoltaic applications. We have changed the concentration of ZnO nanoparticles in 8CB from 1.18 to 40 wt %. Our results show an improvement in the alignment of the liquid crystal with increasing weight percentage of ZnO nanoparticles, up to a concentration of 30 wt %. In addition, the current generated by the system increases by three orders of magnitude.
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61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
72.40.+w Photoconduction and photovoltaic effects
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
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Efficiency dependence on alkali metal compound/Al bilayer cathode in organic light-emitting diodes

D. Y. Zhou, S. D. Cai, W. Gu, L. S. Liao, and S. T. Lee

Appl. Phys. Lett. 97, 223302 (2010); http://dx.doi.org/10.1063/1.3522883 (3 pages) | Cited 1 time

Online Publication Date: 30 November 2010

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The use of alkali metal compound/Al bilayer cathodes of LiF/Al and Liq/Al caused a dramatic luminous efficiency change of one order of magnitude in organic light-emitting diodes (OLEDs) comprising 2-methyl-9,10-bis(naphthalene-2-yl)anthracene (MADN) as an electron-transporting layer (ETL). In contrast, the use of the same two electrodes yielded similar efficiency in OLEDs comprising of tris(8-hydroxyquinoline) aluminum(III) (Alq3) as an ETL. The dramatic change is attributed to different behaviors of LiF/Al and Liq/Al cathodes toward the ETL. It is revealed that organic alkali metal complex/Al, such as Liq/Al, is superior to inorganic alkali metal compound/Al, such as LiF/Al, as a standard bilayer cathode to investigate the effectiveness of electron-transporting materials for high-efficiency OLEDs.
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85.60.Jb Light-emitting devices
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Light out-coupling enhancement of organic light-emitting devices with microlens array

J. P. Yang, Q. Y. Bao, Z. Q. Xu, Y. Q. Li, J. X. Tang, and S. Shen

Appl. Phys. Lett. 97, 223303 (2010); http://dx.doi.org/10.1063/1.3521413 (3 pages) | Cited 1 time

Online Publication Date: 1 December 2010

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Light out-coupling efficiency of organic light-emitting devices from high-index glass substrate into air is enhanced by attaching ordered microlens arrays, which are fabricated by a roll-to-roll mold transfer process. The dependence of microlens geometries on light extraction is analyzed experimentally and theoretically. An increase of 60% in the light out-coupling with an optimized elliptical microlens array is achieved over a conventional device without affecting the electroluminescent spectrum.
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42.79.Bh Lenses, prisms and mirrors
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Spin-polarized charge carrier injection by tunneling from ferromagnetic contacts into organic semiconductors

M. Yunus, P. P. Ruden, and D. L. Smith

Appl. Phys. Lett. 97, 223304 (2010); http://dx.doi.org/10.1063/1.3522657 (3 pages) | Cited 1 time

Online Publication Date: 1 December 2010

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Tunnel-injection of spin-polarized charge carriers from ferromagnetic contacts into organic semiconductors is modeled. Tunneling matrix elements and transition rates for the two spin types are calculated using a transfer Hamiltonian. The tunneling process occurs between extended states of the contact and model “molecular” orbitals. We explore the effects of the tunnel barrier height and of the ferromagnetic contact’s Fermi wave vectors on the level of spin injection. The barrier height and the majority and minority spin Fermi wave vectors of the contact have strong effects on the sign and magnitude of spin injection.
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85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
75.76.+j Spin transport effects
72.25.Mk Spin transport through interfaces
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.10.Dg Crystal-field theory and spin Hamiltonians
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Enhanced performance of inverted polymer solar cells with cathode interfacial tuning via water-soluble polyfluorenes

Seok-In Na, Tae-Soo Kim, Seung-Hwan Oh, Junkyung Kim, Seok-Soon Kim, and Dong-Yu Kim

Appl. Phys. Lett. 97, 223305 (2010); http://dx.doi.org/10.1063/1.3522893 (3 pages) | Cited 2 times

Online Publication Date: 2 December 2010

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Enhanced performance of inverted polymer solar cells (PSCs) is demonstrated by indium tin oxide (ITO) interfacial tuning via a water-soluble polyfluorene (WPF-6-oxy-F). Kelvin probe studies and dark current-voltage curves demonstrated that the WPF-6-oxy-F layer reduces the ITO work-function because of the favorable interfacial dipole formed by the WPF-6-oxy-F interlayer, thereby enhancing the built-in potential and reducing the interface resistance. As a result, introduction of the WPF-6-oxy-F by simple solution processing into the inverted PSCs dramatically enhanced cell-performances. This approach could be very beneficial and an important step for the future development of all-solution-processed or roll-to-roll processed PSCs.
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88.40.jr Organic photovoltaics
88.40.hj Efficiency and performance of solar cells
73.30.+y Surface double layers, Schottky barriers, and work functions
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Thermal nonlinear effects in hybrid optical microresonators

Hong Seok Choi and Andrea M. Armani

Appl. Phys. Lett. 97, 223306 (2010); http://dx.doi.org/10.1063/1.3520467 (3 pages) | Cited 2 times

Online Publication Date: 2 December 2010

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The inherent material properties of silica reduce the susceptibility of silica optical microcavities to many nonlinear phenomena, enabling the development of devices with improved stability. However, large nonlinear coefficients can be leveraged to create microcavities with additional functionality. Therefore, devices with controllable nonlinear behavior are of interest. In the present research, silica microcavities are coated with polystyrene or polymethylmethacrylate to form hybrid microresonators. Using these devices, the thermally induced nonlinear optical behavior is investigated. By precisely controlling the optical field overlap with the polymer film, an environmentally stable device, in which the resonant frequency is independent of the input power, is demonstrated.
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42.79.-e Optical elements, devices, and systems
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
78.20.N- Thermo-optic effects
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Polymer space-charge-limited transistor as a solid-state vacuum tube triode

Yu-Chiang Chao, Ming-Che Ku, Wu-Wei Tsai, Hsiao-Wen Zan, Hsin-Fei Meng, Hung-Kuo Tsai, and Sheng-Fu Horng

Appl. Phys. Lett. 97, 223307 (2010); http://dx.doi.org/10.1063/1.3513334 (3 pages) | Cited 7 times

Online Publication Date: 3 December 2010

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We report the construction of a polymer space-charge-limited transistor (SCLT), a solid-state version of vacuum tube triode. The SCLT achieves a high on/off ratio of 3×105 at a low operation voltage of 1.5 V by using high quality insulators both above and below the grid base electrode. Applying a greater bias to the base increases the barrier potential, and turns off the channel current, without introducing a large parasitic leakage current. Simulation result verifies the influence of base bias on channel potential distribution. The output current density is 1.7 mA/cm2 with current gain greater than 1000.
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84.47.+w Vacuum tubes
85.30.Fg Bulk semiconductor and conductivity oscillation devices (including Hall effect devices, space-charge-limited devices, and Gunn effect devices)
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