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10 Nov 2008

Volume 93, Issue 19, Articles (19xxxx)

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Appl. Phys. Lett. 93, 192501 (2008); http://dx.doi.org/10.1063/1.3013857 (3 pages)

O. Hellwig, A. Moser, E. Dobisz, Z. Z. Bandic, H. Yang, D. S. Kercher, J. D. Risner-Jamtgaard, D. Yaney, and E. E. Fullerton
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Spray-deposited poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) top electrode for organic solar cells

Yee-Fun Lim, Sungsoo Lee, David J. Herman, Matthew T. Lloyd, John E. Anthony, and George G. Malliaras

Appl. Phys. Lett. 93, 193301 (2008); http://dx.doi.org/10.1063/1.3021022 (3 pages) | Cited 31 times

Online Publication Date: 10 November 2008

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Spray deposition is emerging as an attractive low-cost and high throughput method for organic solar cell (OSC) fabrication. In this letter, we demonstrate that a highly conductive formulation of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) can be spray deposited to form the top electrode for an OSC. An inverted solar cell fabricated in this way with a blend of poly(3-hexylthiophene) and [6,6]-phenyl-C61 butyric acid methyl ester as the active layer achieved a power conversion efficiency of 2.0% under AM 1.5 100 mW/cm2 illumination.
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84.60.Jt Photoelectric conversion
82.45.Fk Electrodes
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Polarized emission from high quality microcavity based on active organic layered domains

S. Stelitano, G. De Luca, S. Savasta, and S. Patané

Appl. Phys. Lett. 93, 193302 (2008); http://dx.doi.org/10.1063/1.3026534 (3 pages) | Cited 6 times

Online Publication Date: 10 November 2008

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We demonstrate a giant polarization splitting of the emission of a high quality monolithic microcavity with an embedded ultrathin organic tetrakis(4-methoxyphenyl)porphyrin layer. The usual employed mechanism, based on the mismatch between the center of the mirror stopband and the wavelength of the microcavity, accounts only for a small fraction of the observed splitting. Optical and atomic force microscopy measurements allowed us to attribute it to local crystalline molecular order. This opens the way for the design and optimization of highly polarized compact optical sources.
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78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
78.55.Kz Solid organic materials
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Analysis of efficiency characteristics of green phosphorescent organic light-emitting devices

Ji-hwan Yoon and Il-soo Park

Appl. Phys. Lett. 93, 193303 (2008); http://dx.doi.org/10.1063/1.2998575 (3 pages) | Cited 4 times

Online Publication Date: 11 November 2008

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Efficiency characteristics of green phosphorescent organic light-emitting devices (PHOLEDs) with different host materials and device structures were investigated by examining the luminance efficiency-current density curves and electroluminescence spectra. The efficiency of PHOLEDs at low current density as well as at high current density was greatly affected by energy levels and carrier transport properties of the host and hole/electron transporting materials. The devices exhibited high initial luminance efficiency when hole-electron recombination was well confined in the emitting layer (EML). Efficiency roll off with increasing current density was observed as hole-electron recombination and charge balance in EML deteriorated with current density.
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85.60.Jb Light-emitting devices
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Encapsulation of organic light-emitting devices using a perfluorinated polymer

J. Granstrom, J. S. Swensen, J. S. Moon, G. Rowell, J. Yuen, and A. J. Heeger

Appl. Phys. Lett. 93, 193304 (2008); http://dx.doi.org/10.1063/1.3006349 (3 pages) | Cited 9 times

Online Publication Date: 12 November 2008

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Films of Cytop™, a perfluorinated polymer, are spin cast as a single barrier layer for evaluation of barrier properties on organic light-emitting devices and on Ca thin films. Cytop™ is water repellant, resulting in encapsulated organic light-emitting field effect transistors and organic light-emitting diodes (OLEDs), which remain active even after immersion into water or exposure to water droplets on the Cytop™ surface. OLEDs encapsulated with Cytop™ exhibit up to five times longer continuous operation under identical environmental and driving conditions compared with devices that are not encapsulated with Cytop™.
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85.60.Jb Light-emitting devices
85.30.Tv Field effect devices
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Highly efficient excimer-based white phosphorescent devices with improved power efficiency and color rendering index

Xiaohui Yang, Zixing Wang, Sijesh Madakuni, Jian Li, and Ghassan E. Jabbour

Appl. Phys. Lett. 93, 193305 (2008); http://dx.doi.org/10.1063/1.3013324 (3 pages) | Cited 18 times

Online Publication Date: 12 November 2008

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Power efficiency, Commission Internationale d’Énclairage (CIE) coordinates, and color rendering index (CRI) of white phosphorescent excimer devices were improved by utilizing two platinum complexes as emissive dopants and exploring different device structures. Compared with devices containing two emissive layers each having a different dopant, devices having two dopants incorporated in a single host layer showed better color stability with the change in operating voltage. White phosphorescent excimer devices having the double-doped emissive layer showed an external quantum efficiency and a power efficiency of 14.5% and 17 lm/W, respectively, at 500 cd/m2. The CIE coordinates and CRI of the devices were (0.382, 0.401) and 81, which were almost independent of the drive voltage.
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85.60.Jb Light-emitting devices
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Stacked white organic light emitting devices consisting of separate red, green, and blue elements

Xiangfei Qi, Michael Slootsky, and Stephen Forrest

Appl. Phys. Lett. 93, 193306 (2008); http://dx.doi.org/10.1063/1.3021014 (3 pages) | Cited 24 times

Online Publication Date: 13 November 2008

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We demonstrate a white organic light-emitting device where individual red, green, and blue (R, G, and B) phosphorescent organic light-emitting devices are vertically stacked and electrically interconnected by a compound MoO3/Li-doped charge generation layer. For the order of B, G, and R cells positioned relative to the indium tin oxide anode, the device yields a peak total external quantum efficiency (EQE) and power efficiency (PE) of ηext = (36±2)% at a current density of J = 82 μA/cm2 and ηp = 21±1 lm/W at J = 17 μA/cm2, respectively. The EQE and PE of the device roll off to (32±2)% and 13±1 lm/W at 1000 cd/m2, corresponding to J = 2 mA/cm2. At this luminance, the device shows Commission Internationale de L’Eclairage chromaticity coordinates of (0.45, 0.36) and a color rendering index of 63.
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85.60.Jb Light-emitting devices
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Performance improvement of inverted polymer solar cells with different top electrodes by introducing a MoO3 buffer layer

Chen Tao, Shengping Ruan, Xindong Zhang, Guohua Xie, Liang Shen, Xiangzi Kong, Wei Dong, Caixia Liu, and Weiyou Chen

Appl. Phys. Lett. 93, 193307 (2008); http://dx.doi.org/10.1063/1.3026741 (3 pages) | Cited 64 times

Online Publication Date: 13 November 2008

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Molybdenum trioxide (MoO3) was inserted between the active layer and top electrode in inverted polymer solar cells (PSCs) with nanocrystalline titanium dioxide as an electron selective layer. The performances of structurally identical PSCs with different top electrodes (Au, Ag, and Al) were investigated and compared. The interface between MoO3 and different metals was studied by x-ray photoelectron spectroscopy. The results showed that the performances of devices with different metals are greatly improved due to the incorporation of MoO3 and the open-circuit voltage of devices is relatively insensitive to the choice of the anode metal when MoO3 is introduced.
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84.60.Jt Photoelectric conversion
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Origin of the open-circuit voltage in multilayer heterojunction organic solar cells

W. J. Potscavage, Jr., S. Yoo, and B. Kippelen

Appl. Phys. Lett. 93, 193308 (2008); http://dx.doi.org/10.1063/1.3027061 (3 pages) | Cited 58 times

Online Publication Date: 14 November 2008

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From temperature dependent studies of pentacene/C60 solar cells in the dark, the reverse saturation current is found to be thermally activated with a barrier height that corresponds to the difference in energy between the highest occupied molecular orbital of the donor and the lowest unoccupied molecular orbital of the acceptor corrected for vacuum level misalignments and the presence of charge-transfer states. From the reverse saturation current in the dark and the short-circuit current under illumination, the open-circuit voltage can be predicted. Examination of several donor materials supports the relationship between reverse saturation current, this barrier height, and open-circuit voltage.
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73.50.Pz Photoconduction and photovoltaic effects
73.61.Ph Polymers; organic compounds
84.60.Jt Photoelectric conversion
85.60.Dw Photodiodes; phototransistors; photoresistors
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Investigation of drift in electro-optic polymer waveguides

Roshan Thapliya, Shigetoshi Nakamura, and Takashi Kikuchi

Appl. Phys. Lett. 93, 193309 (2008); http://dx.doi.org/10.1063/1.3027065 (3 pages)

Online Publication Date: 14 November 2008

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The mechanism of the phase drift in electro-optic polymer waveguide devices is presented based on buildup of free ion charge at the electrode-clad interfaces. The difference of the electrode-clad interfaces at the top and bottom electrodes is shown to be important in reducing the drift and that doping of the core with macrocyclic polyethers can suppress this phenomenon. Arrhenius curves of long-term phase drifts using Mach–Zehnder modulators show the activation energies for symmetric electrode interfaces, asymmetric electrode interfaces, and macrocyclic polyether doped cores to be 0.30, 0.28, and 0.15 eV, respectively.
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42.79.Gn Optical waveguides and couplers
42.79.Hp Optical processors, correlators, and modulators
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Band alignment at metal/organic and metal/oxide/organic interfaces

M. G. Helander, Z. B. Wang, J. Qiu, and Z. H. Lu

Appl. Phys. Lett. 93, 193310 (2008); http://dx.doi.org/10.1063/1.3030979 (3 pages) | Cited 27 times

Online Publication Date: 14 November 2008

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Charge injection at metal/organic interfaces dictates the performance, lifetime, and stability of organic electronic devices. We demonstrate that interface dipole theory, originally developed to describe Schottky contacts at metal/semiconductor interfaces, can also accurately describe the injection barriers in real organic electronic devices. It is found that theoretically predicted hole injection barriers for various archetype metal/organic and metal/oxide/organic structures are in excellent agreement with values extracted from experimental transport measurements. Injection barriers at metal/organic and metal/oxide/organic interfaces can therefore be accurately predicted based on the knowledge of only a few fundamental material properties of the oxide and organic layers.
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73.40.Ns Metal-nonmetal contacts
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.30.+y Surface double layers, Schottky barriers, and work functions
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