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12 Mar 2012

Volume 100, Issue 11, Articles (11xxxx)

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Appl. Phys. Lett. 100, 111101 (2012); http://dx.doi.org/10.1063/1.3691957 (3 pages)

Christina Alpmann, Michael Esseling, Patrick Rose, and Cornelia Denz
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Charge depletion in organic heterojunction

T. W. Ng, M. F. Lo, S. T. Lee, and C. S. Lee

Appl. Phys. Lett. 100, 113301 (2012); http://dx.doi.org/10.1063/1.3693608 (3 pages) | Cited 3 times

Online Publication Date: 12 March 2012

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Until now two types of organic-organic heterojunction (OHJ) have been observed in P-N junctions formed between undoped-organic semiconductors. Charge-transfers across OHJs are either negligible or showing electron transfer from P-type to N-type materials, leading to charges accumulation near the interface. Here, we observed that junction of 4,4′,4′′-tris(2-methylphenyl-phenylamino)triphenylamine (m-MTDATA)/bathocuproine (BCP) show the third-behavior. Electrons in BCP (N-type) transfer to m-MTDATA (P-type), leading to depletion of mobile majority carriers near the junction. While “depletion junctions” are typical in inorganic semiconductors, there are no reports in undoped-OHJ. Formation mechanism of depletion OHJs and fundamental differences between inorganic and organic HJs are discussed.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
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Photoelectron spectroscopy investigations of recombination contacts for tandem organic solar cells

Selina Olthof, Ronny Timmreck, Moritz Riede, and Karl Leo

Appl. Phys. Lett. 100, 113302 (2012); http://dx.doi.org/10.1063/1.3693385 (4 pages) | Cited 2 times

Online Publication Date: 14 March 2012

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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.
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88.40.J- Types of solar cells
79.60.Fr Polymers; organic compounds
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
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Light-induced electron paramagnetic resonance evidence of charge transfer in electrospun fibers containing conjugated polymer/fullerene and conjugated polymer/fullerene/carbon nanotube blends

Alexander I. Shames, Céline Bounioux, Eugene A. Katz, Rachel Yerushalmi-Rozen, and Eyal Zussman

Appl. Phys. Lett. 100, 113303 (2012); http://dx.doi.org/10.1063/1.3693520 (4 pages) | Cited 1 time

Online Publication Date: 14 March 2012

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Electrospun sub-micron fibers containing conjugated polymer (poly(3-hexylthiophene), P3HT) with a fullerene derivative, phenyl-C61-butyric acid methylester (PCBM) or a mixture of PCBM and single-walled carbon nanotubes (SWCNTs) were studied by light-induced electron paramagnetic resonance spectroscopy. The results provide experimental evidence of electron transfer between PCBM and P3HT components in both fiber systems and suggest that the presence of a dispersing block-copolymer, which acts via physical adsorption onto the PCBM and SWCNT moieties, does not prevent electron transfer at the P3HT-PCBM interface. These findings suggest a research perspective towards utilization of fibers of functional nanocomposites in fiber-based organic optoelectronic and photovoltaic devices. The latter can be developed in the textile-type large area photovoltaics or individual fiber-based solar cells that will broaden energy applications from macro-power tools to micro-nanoscale power conversion devices and smart textiles.
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76.30.Lh Other ions and impurities
81.05.Ni Dispersion-, fiber-, and platelet-reinforced metal-based composites
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
81.05.ub Fullerenes and related materials
61.46.-w Structure of nanoscale materials
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Visualizing charge movement near organic heterojunctions with ultrafast time resolution via an induced Stark shift

Gary P. Wiederrecht, Noel C. Giebink, Jasmina Hranisavljevic, Daniel Rosenmann, Alex B. F. Martinson, Richard D. Schaller, and Michael R. Wasielewski

Appl. Phys. Lett. 100, 113304 (2012); http://dx.doi.org/10.1063/1.3694287 (4 pages) | Cited 2 times

Online Publication Date: 15 March 2012

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We introduce a method to monitor photoinduced charge separation processes in organic donor-acceptor heterostructures. This approach utilizes a transient Stark shift of the exciton band of a molecular J-aggregate, deposited as a thin probe layer adjacent to the organic heterojunction. The high temporal dynamic range of this approach, from 100 femtoseconds to nanoseconds and longer, enables the entire charge separation process to be followed in both space and time. More broadly, this method can be applied to characterize photoinduced charge injection and separation processes in different materials and architectures, where sub-picosecond time resolution is needed at high spatial resolution.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
78.20.Jq Electro-optical effects
71.35.-y Excitons and related phenomena
71.55.-i Impurity and defect levels
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Subwavelength optical absorber with an integrated photon sorter

J. Le Perchec, Y. Desieres, N. Rochat, and R. Espiau de Lamaestre

Appl. Phys. Lett. 100, 113305 (2012); http://dx.doi.org/10.1063/1.3694749 (4 pages) | Cited 6 times

Online Publication Date: 15 March 2012

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We provide the experimental and theoretical evidence that several nano-patch antennas assembled within a wavelength-scale region may constitute an efficient and easily tunable multi-band photodetector. The system uses highly confined localization states of light and exhibits a robust spectral sorting capability, paving the way to highly integrated hyperspectral imaging.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
42.79.Pw Imaging detectors and sensors
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Influence of inserting a thin fullerene layer on pentacene organic thin-film transistor

Yu-Chang Li, Yu-Ju Lin, Chia-Yu Wei, Dei-Wei Chou, Chun-Ho Tsao, and Yeong-Her Wang

Appl. Phys. Lett. 100, 113306 (2012); http://dx.doi.org/10.1063/1.3693176 (4 pages) | Cited 2 times

Online Publication Date: 15 March 2012

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The performance of organic thin-film transistors (TFTs) with a pentacene/fullerene(C60)/pentacene (PCP) sandwich structure is presented. Using a 3.5 nm-thick C60 layer inserted between the pentacene films, the obtained hole mobility is improved by more than six times. By applying atomic force microscopy, x-ray diffraction, Raman spectrum, and transmission line method analysis, one can reasonably infer that the smoother surface of the pentacene film covered with thin C60 layer delays the phase transformation of the upper pentacene film, resulting in stronger intermolecular coupling and the reduction of channel resistance of the PCP TFTs from 3.03 to 1.72 MΩ, and, therefore, improving the device performance.
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85.30.Tv Field effect devices
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