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8 Oct 2012

Volume 101, Issue 15, Articles (15xxxx)

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Appl. Phys. Lett. 101, 153501 (2012); http://dx.doi.org/10.1063/1.4756693 (3 pages)

Brandon G. Cook, William R. French, and Kálmán Varga
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Optimization of antireflective zinc oxide nanorod arrays on seedless substrate for bulk-heterojunction organic solar cells

Hyung Woo Choi, Kyu-Sung Lee, and T. L. Alford

Appl. Phys. Lett. 101, 153301 (2012); http://dx.doi.org/10.1063/1.4757997 (4 pages)

Online Publication Date: 8 October 2012

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We report on the enhanced performance of hybrid photovoltaic devices consisting of poly(3-hexylthiophene), (6,6)-phenyl C61 butyric acid methyl ester, and zinc oxide (ZnO) nanorod arrays grown on seedless indium tin oxide (ITO) glass in aqueous zinc chloride solution. Introduction of optimized-length ZnO nanorod arrays between hole injection and ITO layers increased photocurrent density from 8.0 to 8.8 mA/cm2 and fill factor from 42% to 47%. The absence of a seed layer significantly reduced incident light reflection on the ITO glass and resulted in an overall 10% increase in photocurrent. A photovoltaic device based on a ZnO nanostructure length of 100 nm exhibited a maximum power conversion efficiency of 2.4%, 15% higher than that of an equivalent device without ZnO nanorods.
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88.40.H- Solar cells (photovoltaics)
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Localizing trapped charge carriers in NO2 sensors based on organic field-effect transistors

Anne-Marije Andringa, W. S. Christian Roelofs, Michael Sommer, Mukundan Thelakkat, Martijn Kemerink, and Dago M. de Leeuw

Appl. Phys. Lett. 101, 153302 (2012); http://dx.doi.org/10.1063/1.4758697 (5 pages)

Online Publication Date: 8 October 2012

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Field-effect transistors have emerged as NO2 sensors. The detection relies on trapping of accumulated electrons, leading to a shift of the threshold voltage. To determine the location of the trapped electrons we have delaminated different semiconductors from the transistors with adhesive tape and measured the surface potential of the revealed gate dielectric with scanning Kelvin probe microscopy. We unambiguously show that the trapped electrons are not located in the semiconductor but at the gate dielectric. The microscopic origin is discussed. Pinpointing the location paves the way to optimize the sensitivity of NO2 field-effect sensors.
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82.80.-d Chemical analysis and related physical methods of analysis
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
85.30.Tv Field effect devices
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
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Rhenium oxide as an efficient p-dopant to overcome S-shaped current density-voltage curves in organic photovoltaics with a deep highest occupied molecular orbital level donor layer

Dae-Ho Kim, Tae-Min Kim, Won-Ik Jeong, and Jang-Joo Kim

Appl. Phys. Lett. 101, 153303 (2012); http://dx.doi.org/10.1063/1.4758681 (4 pages)

Online Publication Date: 9 October 2012

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Effect of p-dopants in a p-doped hole transport layer inserted between indium tin oxide and a donor layer of α,α′-bis(2,2-dicyanovinyl)-quinquethiophene with a deep highest occupied molecular orbital level is reported to remove the S-shape in the organic photovoltaics (OPV) cell. Among the p-dopants of ReO3, MoO3, WO3, and CuI, ReO3 possesses the largest work function and turns out to be the most efficient p-dopant to remove the S-shape of the current density-voltage curve in the OPV cells. The rest of the dopants could not get rid of the S-shape, even with a doping concentration of 25 mol. %. The difference among the dopants can be understood by the different charge generation efficiency of the dopants.
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88.40.jr Organic photovoltaics
88.40.hj Efficiency and performance of solar cells
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Organic light-emitting diodes with direct contact-printed red, green, blue, and white light-emitting layers

Sun-Zen Chen, Shiang-Hau Peng, Tzu-Yu Ting, Po-Shien Wu, Chun-Hao Lin, Chin-Yeh Chang, Jing-Jong Shyue, and Jwo-Huei Jou

Appl. Phys. Lett. 101, 153304 (2012); http://dx.doi.org/10.1063/1.4757279 (4 pages)

Online Publication Date: 9 October 2012

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We demonstrate the feasibility of using direct contact-printing in the fabrication of monochromatic and polychromatic organic light-emitting diodes (OLEDs). Bright devices with red, green, blue, and white contact-printed light-emitting layers with a respective maximum luminance of 29 000, 29 000, 4000, and 18 000 cd/m2 were obtained with sound film integrity by blending a polymeric host into a molecular host. For the red OLED as example, the maximum luminance was decreased from 29 000 to 5000 cd/m2 as only the polymeric host was used, or decreased to 7000 cd/m2 as only the molecular host was used. The markedly improved device performance achieved in the devices with blended hosts may be attributed to the employed polymeric host that contributed a good film-forming character, and the molecular host that contributed a good electroluminescence character.
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85.60.Jb Light-emitting devices
85.65.+h Molecular electronic devices
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Improvement of amplified spontaneous emission performance of conjugated polymer waveguides with a low loss cladding

Bo Zhang, Yanbing Hou, Zhidong Lou, Feng Teng, Xiaojun Liu, Lingchuan Meng, Jingling Shen, and Yongsheng Wang

Appl. Phys. Lett. 101, 153305 (2012); http://dx.doi.org/10.1063/1.4758927 (4 pages) | Cited 1 time

Online Publication Date: 10 October 2012

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We report the improvement of the amplified spontaneous emission (ASE) performance in the optically pumped symmetric thin film waveguide glass/indium-tin oxide (ITO)/SiO2/poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene]/SiO2/Al or Ag by optimizing the thickness of SiO2 and replacing the Al electrode with Ag, where SiO2 acted as a spacer layer to prevent the ASE at 620 nm from being destructed. The results show that the SiO2/Ag cladding reduced the ASE threshold to 4 μJ/pulse compared with the SiO2/Al cladding, owing to the higher work function and reflection rate as well as lower absorption loss of the Ag electrode. No photoluminescence at 580 nm being observed makes it possible for an electric field to only modulate the ASE at 620 nm in the device with the SiO2/Ag cladding. The electric-field quenching of the ASE has been observed, which increases with the electric field. The field dependence of ASE can be attributed to field-induced dissociation of photogenerated excitons in the polymer waveguides.
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42.79.Gn Optical waveguides and couplers
81.65.-b Surface treatments
71.20.Rv Polymers and organic compounds
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
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Increased efficiency of light-emitting diodes incorporating anodes functionalized with fluorinated azobenzene monolayers and a green-emitting polyfluorene derivative

G. M. Lazzerini, S. Mian, F. Di Stasio, A. Merari Masillamani, N. Crivillers, F. Reinders, M. Mayor, P. Samorì, and F. Cacialli

Appl. Phys. Lett. 101, 153306 (2012); http://dx.doi.org/10.1063/1.4758682 (5 pages) | Cited 1 time

Online Publication Date: 10 October 2012

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We investigate the functionalization of gold anodes with azobenzene-based self-assembled monolayers (AZO-SAM) and the influence of such functionalization on the external quantum efficiency (EQE) of polyfluorene-based light-emitting diodes (LEDs). Photoluminescence and electroluminescence measurements show that the AZO-SAMs do not modify the shape of the emission spectrum of the active layer. Instead, AZO-SAMs enhance the EQE of LEDs by an order of magnitude (from 0.018% to 0.18%) and decrease the turn-on voltage from 7.9 V to 6.2 V by reducing the injection barrier at the anode, thus promoting a better balance between hole and electron populations in the active layer.
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85.60.Jb Light-emitting devices
68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces
78.66.Qn Polymers; organic compounds
78.55.Kz Solid organic materials
78.60.Fi Electroluminescence
82.45.Fk Electrodes
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Semitransparent polymer solar cells with one-dimensional (WO3/LiF)N photonic crystals

Wenjuan Yu, Liang Shen, Yongbing Long, Wenbin Guo, Fanxu Meng, Shengping Ruan, Xu Jia, Hongshi Ma, and Weiyou Chen

Appl. Phys. Lett. 101, 153307 (2012); http://dx.doi.org/10.1063/1.4760229 (4 pages) | Cited 2 times

Online Publication Date: 11 October 2012

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One-dimensional (WO3/LiF)N photonic crystals (1DPCs) are deposited on the Ag cathode of the semitransparent polymer solar cells to improve the efficiency of the device. The 1DPCs with 8 pair of WO3/LiF act as distributed reflectors within the photonic bandgap. Then, power conversion efficiency of 2.58% is achieved and there is an improvement of 26.3% in the efficiency when compared with that of the conventional device without the 1DPCs. The average transmittance of the device with 8 pair of WO3/LiF is almost zero in 400–600 nm wavelength range. It means that the light is absorbed sufficiently in the active layer. The enhanced light absorption results in efficiency improvement remarkably.
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88.40.jr Organic photovoltaics
88.40.hj Efficiency and performance of solar cells
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