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28 Feb 2011

Volume 98, Issue 9, Articles (09xxxx)

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Appl. Phys. Lett. 98, 093502 (2011); http://dx.doi.org/10.1063/1.3531756 (3 pages)

Marina S. Leite, Robyn L. Woo, William D. Hong, Daniel C. Law, and Harry A. Atwater
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Determination of the trap-assisted recombination strength in polymer light emitting diodes

Martijn Kuik, Herman T. Nicolai, Martijn Lenes, Gert-Jan A. H. Wetzelaer, Mingtao Lu, and Paul W. M. Blom

Appl. Phys. Lett. 98, 093301 (2011); http://dx.doi.org/10.1063/1.3559911 (3 pages) | Cited 15 times

Online Publication Date: 28 February 2011

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The recombination processes in poly(p-phenylene vinylene) based polymer light-emitting diodes (PLEDs) are investigated. Photogenerated current measurements on PLED device structures reveal that next to the known Langevin recombination also trap-assisted recombination is an important recombination channel in PLEDs, which has not been considered until now. The dependence of the open-circuit voltage on light intensity enables us to determine the strength of this process. Numerical modeling of the current-voltage characteristics incorporating both Langevin and trap-assisted recombination yields a correct and consistent description of the PLED, without the traditional correction of the Langevin prefactor. At low bias voltage the trap-assisted recombination rate is found to be dominant over the free carrier recombination rate.
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85.60.Jb Light-emitting devices
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Influence of self-assembled monolayer dielectrics on the morphology and performance of α,ω-dihexylquaterthiophene in thin film transistors

Michael Novak, Thomas Schmaltz, Hendrik Faber, and Marcus Halik

Appl. Phys. Lett. 98, 093302 (2011); http://dx.doi.org/10.1063/1.3560454 (3 pages) | Cited 5 times

Online Publication Date: 1 March 2011

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Three different ultrathin hybrid dielectrics based on self-assembled monolayers (SAMs) from phosphonic acid molecules were investigated on aluminum oxide. The impact of the underlying SAMs on the semiconductor morphology and transistor device performance was studied by reducing the film thickness of the subsequently deposited α,ω-dihexylquaterthiophene semiconductor to one monolayer and less. The nature of the SAM relates to the molecular orientation of submonolayer films, which is investigated by photoluminescence microscopy and atomic force microscopy. SAMs with high surface energy tend to induce a face-on growing of the semiconductor, whereas for SAMs with low surface energy an edge-on growth is favorable.
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85.30.Tv Field effect devices
68.55.jd Thickness
78.66.Qn Polymers; organic compounds
78.55.Kz Solid organic materials
68.35.Md Surface thermodynamics, surface energies
68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces
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Thermoelectric and bulk mobility measurements in pentacene thin films

G.-H. Kim, M. Shtein, and K. P. Pipe

Appl. Phys. Lett. 98, 093303 (2011); http://dx.doi.org/10.1063/1.3556622 (3 pages) | Cited 4 times

Online Publication Date: 2 March 2011

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Low-noise thermoelectric and electrical measurements were used to derive the dependences of Seebeck coefficient and hole mobility on carrier concentration and grain size in the “bulk” regions of thermally evaporated pentacene thin films (in contrast to the channel field-effect mobility typically measured using thin-film transistor geometries). Distinct charge transport regimes were observed for larger (0.5 and 0.8 μm) and smaller (0.2 μm) grain sizes, attributed to carrier-dopant scattering and percolation, respectively.
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72.20.Pa Thermoelectric and thermomagnetic effects
73.50.Lw Thermoelectric effects
72.20.Fr Low-field transport and mobility; piezoresistance
73.61.Ph Polymers; organic compounds
61.72.-y Defects and impurities in crystals; microstructure
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Threshold optimization of polymeric opal photonic crystal cavity as organic solid-state dye-doped laser

Lan-Ting Shi, Feng Jin, Mei-Ling Zheng, Xian-Zi Dong, Wei-Qiang Chen, Zhen-Sheng Zhao, and Xuan-Ming Duan

Appl. Phys. Lett. 98, 093304 (2011); http://dx.doi.org/10.1063/1.3561752 (3 pages) | Cited 2 times

Online Publication Date: 4 March 2011

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The authors have demonstrated the optimization of the active layer thickness on the threshold of organic solid-state dye-doped laser (SSDL), which was fabricated by three-dimensional polymeric opal photonic crystal and tert-butyl Rhodamine B (t-Bu-RhB) doped polymer film. Gain media were produced by incorporating t-Bu-RhB into polymer film at 3.0 wt %. The sandwiched laser resonator cavities with different active layer thickness displayed single-mode lasing oscillations in the reflection band gap of the resonator structure. The lasing threshold as low as 1.13 μJ/pulse was achieved. The optimization of active layer would provide an opportunity to accelerate the development of low threshold polymeric SSDLs.
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42.55.Tv Photonic crystal lasers and coherent effects
42.60.By Design of specific laser systems
42.70.Hj Laser materials
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.70.Qs Photonic bandgap materials
42.70.Jk Polymers and organics
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Thermal boundary resistance of copper phthalocyanine-metal interface

Y. Jin, A. Yadav, K. Sun, H. Sun, K. P. Pipe, and M. Shtein

Appl. Phys. Lett. 98, 093305 (2011); http://dx.doi.org/10.1063/1.3555449 (3 pages) | Cited 4 times

Online Publication Date: 4 March 2011

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Systems containing interfaces between dissimilar materials can exhibit lower thermal conductivity than their pure constituents, with important implications for thermal management and thermoelectric energy conversion. However, the heat transfer processes at such interfaces, in particular those between organic and inorganic materials, remain for the most part uncharacterized. We use vacuum thermal evaporation to grow archetypal multilayer thin films of copper phthalocyanine (CuPc) and Ag or Al, and measure their thermal conductivity as a function of interface density. We observe large thermal boundary resistance values (7.8×10−8 m2 K/W for CuPc/Ag and 2.0×10−8 m2 K/W for CuPc/Al), attributable to acoustic mismatch, heat carrier mismatch, and weak bonding.
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66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
81.15.Dj E-beam and hot filament evaporation deposition
68.35.Ct Interface structure and roughness
68.65.Ac Multilayers
68.60.Bs Mechanical and acoustical properties
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Growth rate dependent trap density in polythiophene-fullerene solar cells and its implications

Kanwar S. Nalwa, Rakesh C. Mahadevapuram, and Sumit Chaudhary

Appl. Phys. Lett. 98, 093306 (2011); http://dx.doi.org/10.1063/1.3560483 (3 pages) | Cited 9 times

Online Publication Date: 4 March 2011

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To understand the effect of processing conditions such as spin coating speed and drying rate on the density of defects; poly(3-hexylthiophene):fullerene-derivative solar cells A, B, and C were fabricated with solvent drying times of ∼ 40 min, 7 min, and 1 min, respectively. We show that slowest grown device A has one order of magnitude less subband gap traps than device C. The open circuit voltage and its light intensity dependence was strongly affected by interfacial recombination of carriers at subgap defect states. The losses due to trap-assisted recombination can even dominate over bimolecular recombination, depending on the density of defect states
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88.40.jr Organic photovoltaics
88.40.H- Solar cells (photovoltaics)
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