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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: 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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  • 5
    Language: English
    In: Energy Policy, Nov, 2013, Vol.62, p.1570-1580
    Keywords: Renewable Energy -- Government Finance ; Renewable Energy -- Planning ; Photovoltaic Cells -- Design And Construction
    ISSN: 0301-4215
    Source: Cengage Learning, Inc.
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  • 6
    Language: English
    In: Energy Policy, Nov, 2013, Vol.62, p.1570-1580
    Keywords: Renewable Energy -- Government Finance ; Renewable Energy -- Planning ; Photovoltaic Cells -- Design And Construction
    ISSN: 0301-4215
    Source: Cengage Learning, Inc.
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  • 7
    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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  • 8
    Language: English
    In: Physical Review B, 4/2012, Vol.85(15)
    Description: We investigate the role charge carrier mobility plays for loss mechanisms in organic bulk heterojunction solar cells. For this purpose, we perform drift-diffusion calculations for several recombination models and properties of the contacts. We show that in case of selective contacts, higher mobilities increase device efficiency, independent of injection barrier heights, energy level bending at the contacts, and the amount of background dark carriers in the device. Nonselective contacts provide a source of photocarrier loss at the "wrong" electrode. This is evident from a decrease of the open-circuit voltage (V sub(oc)) with an increased role of charge carrier diffusion, which originates from a higher mobility or from interface barriers reducing the built-in potential. In this case, V sub(oc) furthermore depends on the device thickness. Considering the effect of different recombination models, a too high mobility of one charge carrier decreases V sub(oc) significantly for Langevin recombination. That is why balanced mobilities are desirable for high efficiency in this case. In presence of recombination via CT states, V sub(oc) is mainly governed by the dynamics of the charge transfer state. Based on these differentiations we show that the existence of an optimum mobility derived from simulation depends strongly on the assumptions made for contact and recombination properties and obtain a comprehensive picture how charge carrier mobility influences the parameters of organic solar cells.
    Keywords: Drift ; Solar Cells ; Devices ; Contact ; Electric Potential ; Charge Carriers ; Volatile Organic Compounds ; Photovoltaic Cells ; Condensed Matter Physics (General) (So) ; Physics of Metals (MD) ; Atomic Properties (Ep) ; Atomic Properties (Ed) ; Atomic Properties (EC) ; Electronics and Communications Milieux (General) (Ea) ; Solid-State Physics (Ah);
    ISSN: 1098-0121
    E-ISSN: 1550-235X
    Source: American Physical Society (APS) (via CrossRef)
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  • 9
    Language: English
    In: Applied Physics Letters, 27 February 2012, Vol.100(9)
    Description: We present two organic dimetal complexes Cr 2 (hpp) 4 and W 2 (hpp) 4 as n-dopants investigated in the model system of fullerene C 60 for the application in organic electronic devices. Conductivity and Seebeck measurements on doped layers are carried out in vacuum at different doping concentrations and various substrate temperatures to compare the two dopants. Very high conductivities of up to 4 S/cm are achieved for both organic dopants. The thermal activation energy of the conductivity as well as the measured Seebeck coefficient are found to decrease with increasing doping concentration, indicating a shift of the Fermi level towards the electron transport level of the n-doped C 60 .
    Keywords: Organic Electronics And Photonics
    ISSN: 0003-6951
    E-ISSN: 1077-3118
    Source: © 2012 American Institute of Physics (AIP)〈img src=http://exlibris-pub.s3.amazonaws.com/AIP_edited.gif style="vertical-align:middle;margin-left:7px"〉
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  • 10
    Language: English
    In: Applied Physics Letters, 12 March 2012, Vol.100(11)
    Description: Recombination contacts play an important role in highly efficient organic tandem solar cells. We present a photoelectron spectroscopy study on contact systems that have previously been shown to work efficiently as recombination contacts. Here, the conversion of an electron current into a hole current is realized either by insertion of gold clusters or by a highly doped pn-junction. From the measured energy level alignments, we show that the working principles of these two approaches are significantly different. For gold clusters, the recombination current is promoted by an accumulation of charge carriers, while for doped pn-junctions, it is achieved by tunneling through a depletion layer.
    Keywords: Organic Electronics And Photonics
    ISSN: 0003-6951
    E-ISSN: 1077-3118
    Source: © 2012 American Institute of Physics (AIP)〈img src=http://exlibris-pub.s3.amazonaws.com/AIP_edited.gif style="vertical-align:middle;margin-left:7px"〉
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