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  • 1
    Language: English
    In: Journal of the American Chemical Society, 07 March 2012, Vol.134(9), pp.3999-4002
    Description: 2-(2-Methoxyphenyl)-1,3-dimethyl-1H-benzoimidazol-3-ium iodide (o-MeO-DMBI-I) was synthesized and employed as a strong n-type dopant for fullerene C(60), a well-known n-channel semiconductor. The coevaporated thin films showed a maximum conductivity of 5.5 S/cm at a doping concentration of 8.0 wt% (14 mol%), which is the highest value reported to date for molecular n-type conductors. o-MeO-DMBI-I can be stored and handled in air for extended periods without degradation and is thus promising for various organic electronic devices.
    Keywords: Membranes, Artificial ; Benzimidazoles -- Chemistry
    ISSN: 00027863
    E-ISSN: 1520-5126
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  • 2
    Language: English
    In: Journal of Applied Physics, 15 December 2011, Vol.110(12)
    Description: We introduce 2,3,8,9,14,15-hexachloro-5,6,11,12,17,18-hexaazatrinaphthylene (HATNA- Cl 6 ) as n-dopable electron transport material (ETM) for small molecule organic solar cells. Because of its large optical energy gap of 2.7 eV and its well suited energy level positions, the material can be implemented as a semitransparent spacer layer between the reflecting metal contact and the photoactive C 60 acceptor layer in p-i-n type solar cells. By varying the ETM thickness, it is possible to shift the position of the photoactive area with respect to the interference maximum of the optical field distribution. Applying n-HATNA- Cl 6 instead of the parasitically absorbing reference ETM n- C 60 results in a considerably improved photocurrent density and accordingly in a higher efficiency. At d ETM = 100 nm the power conversion efficiency is more than doubled as it increases from (100 nm n- C 60 ) = 0.5% to (100 nm n-HATNA- Cl 6 ) = 1.1%.
    Keywords: Articles
    ISSN: 0021-8979
    E-ISSN: 1089-7550
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  • 3
    Language: English
    In: Journal of the American Chemical Society, 04 April 2012, Vol.134(13), pp.6052-6
    Description: By performing microscopic charge transport simulations for a set of crystalline dicyanovinyl-substituted oligothiophenes, we find that the internal acceptor-donor-acceptor molecular architecture combined with thermal fluctuations of dihedral angles results in large variations of local electric fields, substantial energetic disorder, and pronounced Poole-Frenkel behavior, which is unexpected for crystalline compounds. We show that the presence of static molecular dipoles causes large energetic disorder, which is mostly reduced not by compensation of dipole moments in a unit cell but by molecular polarizabilities. In addition, the presence of a well-defined π-stacking direction with strong electronic couplings and short intermolecular distances turns out to be disadvantageous for efficient charge transport since it inhibits other transport directions and is prone to charge trapping.
    Keywords: Chemistry;
    ISSN: 00027863
    E-ISSN: 1520-5126
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  • 4
    Language: English
    In: Journal of Applied Physics, 01 February 2012, Vol.111(3)
    Description: Exciton generation and transfer processes in a multilayer organic light-emitting diode (OLED) are studied in order to realize OLEDs with warm white color coordinates and high color-rendering index (CRI). We investigate a host-guest-system containing four phosphorescent emitters and two matrix materials with different transport properties. We show, by time-resolved spectroscopy, that an energy back-transfer from the blue emitter to the matrix materials occurs, which can be used to transport excitons to the other emitter molecules. Furthermore, we investigate the excitonic and electronic transfer processes by designing suitable emission layer stacks. As a result, we obtain an OLED with Commission Internationale de lÉclairage (CIE) coordinates of (0.444;0.409), a CRI of 82, and a spectrum independent of the applied current. The OLED shows an external quantum efficiency of 10% and a luminous efficacy of 17.4 lm/W at 1000 cd/m 2 .
    Keywords: Articles
    ISSN: 0021-8979
    E-ISSN: 1089-7550
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  • 5
    Language: English
    In: Journal of Applied Physics, Feb 15, 2012, Vol.111(4), p.044507-1-044507-8
    Description: The article presents a complete study of the bidirectional transmission properties exhibited by the different vertical organic triodes (VOTs). The VOTs are shown to be extremely beneficial for solving problems of low current densities and switching speed in current organic field effect transistors (OFETs).
    Keywords: Aluminum (Metal) -- Optical Properties ; Aluminum (Metal) -- Thermal Properties ; Frequency Modulation -- Measurement ; Fullerenes -- Usage ; Plasma Dynamics -- Analysis ; Triodes -- Usage
    ISSN: 0021-8979
    Source: Cengage Learning, Inc.
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  • 6
    Language: English
    In: Applied Physics Letters, 11 August 2014, Vol.105(6)
    Description: The efficiency of organic solar cells can be increased by serial stacked subcells even upon using the same absorber material. For the multi-junction devices presented here, we use the small molecule donor material DCV5T-Me. The subcell currents were matched by optical transfer matrix simulation, allowing an efficiency increase from 8.3% for a single junction up to 9.7% for a triple junction cell. The external quantum efficiency of the subcells, measured under appropriate light bias illumination, is spectrally shifted due to the microcavity of the complete stack, resulting in a broadband response and an increased cell current. The increase of the power conversion efficiency upon device stacking is even stronger for large area cells due to higher influence of the resistance of the indium tin oxide anode, emphasizing the advantage of multi-junction devices for large-area applications.
    Keywords: Organic Electronics And Photonics
    ISSN: 0003-6951
    E-ISSN: 1077-3118
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  • 7
    Language: English
    In: Applied Physics Letters, 22 April 2013, Vol.102(16)
    Description: We investigate the dominating recombination mechanisms in bulk heterojunction solar cells, using a blend of ZnPc and C 60 as model system. Analyzing the open-circuit voltage ( V oc ) as a function of illumination intensity, we find that trap-assisted recombination dominates for low light intensities, whereas at 1 sun, direct/bimolecular recombination becomes important. The recombination parameters are not significantly influenced by the blend mixing ratio and are also valid for injected charges. By changing the hole transport layer, recombination at the contact is separately identified as further mechanism reducing V oc at higher light intensities.
    Keywords: Energy Conversion And Storage
    ISSN: 0003-6951
    E-ISSN: 1077-3118
    Source: © 2013 AIP Publishing LLC (AIP)〈img src=http://exlibris-pub.s3.amazonaws.com/AIP_edited.gif style="vertical-align:middle;margin-left:7px"〉
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  • 8
    Language: English
    In: Applied Physics Letters, 09 March 2015, Vol.106(10)
    Description: Organic field-effect transistors constitute a vibrant research field and open application perspectives in flexible electronics. For a commercial breakthrough, however, significant performance improvements are still needed, e.g., stable and high charge carrier mobility and on-off ratio, tunable threshold voltage, as well as integrability criteria such as n- and p-channel operation and top-gate architecture. Here, we show pentacene-based top-gate organic transistors operated in depletion and inversion regimes, realized by doping source and drain contacts as well as a thin layer of the transistor channel. By varying the doping concentration and the thickness of the doped channel, we control the position of the threshold voltage without degrading on-off ratio or mobility. Capacitance-voltage measurements show that an inversion channel can indeed be formed, e.g., an n-doped channel can be inverted to a p-type inversion channel with highly p-doped contacts. The Cytop polymer dielectric minimizes hysteresis, and the transistors can be biased for prolonged cycles without a shift of threshold voltage, indicating excellent operation stability.
    Keywords: Organic Electronics And Photonics
    ISSN: 0003-6951
    E-ISSN: 1077-3118
    Source: © 2015 AIP Publishing LLC (AIP)
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  • 9
    In: Nature Nanotechnology, 2015, Vol.10(7), p.574
    ISSN: 1748-3387
    Source: Nature Publishing Group
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  • 10
    Language: English
    In: Journal of the American Chemical Society, July 11, 2012, Vol.134(27), p.11064-11067
    Description: The novel methyl-substituted dicyanovinyl-capped quinquethiophenes is performed to obtain highly efficient organic solar cells with power conversion efficiencies of 4.8-6.9%. X-ray analysis of single crystals and evaporated neat and blend films provide insights into the packing and morphological behavior of the novel compounds that rationalized their improved photovoltaic performance.
    Keywords: Electron-electron Interactions -- Analysis ; Methyl Compounds -- Electric Properties ; Methyl Compounds -- Thermal Properties ; Oligomers -- Structure ; Oligomers -- Chemical Properties ; Solar Cells -- Innovations ; X-ray Diffraction -- Methods
    ISSN: 0002-7863
    Source: Cengage Learning, Inc.
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