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17 Oct 2011

Volume 99, Issue 16, Articles (16xxxx)

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Appl. Phys. Lett. 99, 163301 (2011); http://dx.doi.org/10.1063/1.3651509 (3 pages)

Jonathan E. Allen, Kevin G. Yager, Htay Hlaing, Chang-Yong Nam, Benjamin M. Ocko, and Charles T. Black
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Enhanced charge collection in confined bulk heterojunction organic solar cells

Jonathan E. Allen, Kevin G. Yager, Htay Hlaing, Chang-Yong Nam, Benjamin M. Ocko, and Charles T. Black

Appl. Phys. Lett. 99, 163301 (2011); http://dx.doi.org/10.1063/1.3651509 (3 pages) | Cited 9 times

Online Publication Date: 17 October 2011

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Confining blended poly(3-hexylthiophene) and [6,6]-phenyl-C61-butyric acid methyl ester organic solar cell active layers within nanometer-scale cylindrical pores nearly double the supported short-circuit photocurrent density compared to equivalent unconfined volumes of the same blend and increases the poly(3-hexylthiophene) hole mobility in the blend by nearly 500 times. Grazing incidence x-ray diffraction measurements show that the confinement changes the polymer orientation distribution, suppressing low charge conductivity orientations while simultaneously disrupting polymer ordering.
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88.40.jr Organic photovoltaics
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Evidence for non-isotropic emitter orientation in a red phosphorescent organic light-emitting diode and its implications for determining the emitter’s radiative quantum efficiency

Tobias D. Schmidt, Daniel S. Setz, Michael Flämmich, Jörg Frischeisen, Dirk Michaelis, Benjamin C. Krummacher, Norbert Danz, and Wolfgang Brütting

Appl. Phys. Lett. 99, 163302 (2011); http://dx.doi.org/10.1063/1.3653475 (3 pages) | Cited 7 times

Online Publication Date: 18 October 2011

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The efficiency of organic light-emitting diodes is limited as only a fraction of the consumed electrical power is converted into light that is finally extracted to air. Especially, the radiative quantum efficiency of the guest-host system is of interest and should be close to unity to achieve highly efficient devices. We show that the red phosphorescent emitter Ir(MDQ)2(acac) doped in an α-NPD matrix exhibits a profound non-isotropic dipole orientation. Ignoring this feature leads to a significant overestimation of the emitter efficiency. Furthermore, we demonstrate the huge potential for efficiency enhancement of mainly parallel emitter orientation in phosphorescent organic light-emitting diodes.
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85.60.Jb Light-emitting devices
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Realization of high efficiency orange and white organic light emitting diodes by introducing an ultra-thin undoped orange emitting layer

Yongbiao Zhao, Jiangshan Chen, and Dongge Ma

Appl. Phys. Lett. 99, 163303 (2011); http://dx.doi.org/10.1063/1.3654150 (3 pages) | Cited 9 times

Online Publication Date: 19 October 2011

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In this paper, we report on high efficiency orange and white organic light emitting diodes (OLEDs) by introducing an ultra-thin undoped orange emitting layer (less than 1 nm) adjacent to the electron-transporting layer. The orange OLEDs showed a high external quantum efficiency (EQE) of 16.4% at 1000 cd/m2, and the resulting four-color white OLEDs emitted an EQE of 15.5% and a maximum color render index (CRI) of 87 at luminance of 1000 cd/m2. Further analysis on the EQE of the white OLEDs makes us confident that this design has the possibility to realize 100% internal quantum efficiency (IQE) by using much more highly efficient phosphorescent emitters.
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85.60.Jb Light-emitting devices
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High speed and high density organic electrochemical transistor arrays

Dion Khodagholy, Moshe Gurfinkel, Eleni Stavrinidou, Pierre Leleux, Thierry Herve, Sébastien Sanaur, and George G. Malliaras

Appl. Phys. Lett. 99, 163304 (2011); http://dx.doi.org/10.1063/1.3652912 (3 pages) | Cited 4 times

Online Publication Date: 19 October 2011

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A generic lithographic process is presented that allows the fabrication of high density organic electrochemical transistor arrays meant to interface with aqueous electrolytes. The channels of the transistors, which were 6 μm long, were made of the conducting polymer poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonate) and were in direct contact with phosphate buffered saline. Source and drain electrodes and interconnects were insulated by parylene C, a biocompatible material. The transistors operated at low voltages and showed a response time of the order of 100 μs.
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85.30.Tv Field effect devices
85.40.Hp Lithography, masks and pattern transfer
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High performance polymer light-emitting diodes with N-type metal oxide/conjugated polyelectrolyte hybrid charge transport layers

Ji Sun Park, Bo Ram Lee, Eunjae Jeong, Hyun-Jung Lee, Ju Min Lee, Ji-Seon Kim, Jin Young Kim, Han Young Woo, Sang Ouk Kim, and Myoung Hoon Song

Appl. Phys. Lett. 99, 163305 (2011); http://dx.doi.org/10.1063/1.3653962 (3 pages) | Cited 4 times

Online Publication Date: 20 October 2011

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We present an interfacial engineering strategy employing n-type-metal-oxide/conjugated-polyelectrolyte (CPE) hybrid charge-transport layers for highly efficient polymer light-emitting diodes (PLEDs). The hybrid metal-oxide/CPE layer facilitates electron-injection, while blocking hole-transport, and thereby maximizes electron-hole recombination within the emitting layer. A series of metal-oxide/CPE combinations were tested in inverted PLEDs (FTO/metal-oxide/CPE/F8BT/MoO3/Au). Specifically, HfO2/CPE double layer achieved an electroluminescence (EL) efficiency of up to 25.8 cd/A (@ 6.4 V, one of the highest values reported for fluorescent PLEDs).
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85.60.Jb Light-emitting devices
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Extension of the spectral responsivity of the photocurrent in solution-processed small molecule composite via a charge transfer excitation

Gerardo Hernandez-Sosa, Minghong Tong, Nelson E. Coates, Sebastian Valouch, and Daniel Moses

Appl. Phys. Lett. 99, 163306 (2011); http://dx.doi.org/10.1063/1.3655681 (3 pages) | Cited 1 time

Online Publication Date: 20 October 2011

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Incorporating [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) in solution-processed composites comprising the two small molecular semiconductors 9,10-Diphenylanthracene (DPA) and 5,6,11,12-tetraphenylnaphthacene (Rubrene) extends significantly the onset wavelength of the steady-state photoconductivity from 610 nm in the pristine DPA:Rubrene composite to 900 nm in the DPA:Rubrene:PCBM composite. The experimental data indicate carrier generation in the near IR spectral region arising from inter-molecular charge transfer (IMCT) excitation that potentially could be useful for extending solar radiation light harvesting. Pump/probe photoinduced absorption (PIA) measurements indicate instantaneous carrier generation at sub-band-gap photon energies, confirming the viability of IMCT excitations as the underlying carrier generation mechanism at the near IR spectral region.
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84.60.Jt Photoelectric conversion
78.56.-a Photoconduction and photovoltaic effects
72.40.+w Photoconduction and photovoltaic effects
78.66.Qn Polymers; organic compounds
78.66.Sq Composite materials
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