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10 May 2010

Volume 96, Issue 19, Articles (19xxxx)

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Appl. Phys. Lett. 96, 193101 (2010); http://dx.doi.org/10.1063/1.3425776 (3 pages)

J. J. Zhang, N. Hrauda, H. Groiss, A. Rastelli, J. Stangl, F. Schäffler, O. G. Schmidt, and G. Bauer
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Charge carrier densities in chemically doped organic semiconductors verified by two independent techniques

M. Lehnhardt, S. Hamwi, M. Hoping, J. Reinker, T. Riedl, and W. Kowalsky

Appl. Phys. Lett. 96, 193301 (2010); http://dx.doi.org/10.1063/1.3427416 (3 pages) | Cited 6 times

Online Publication Date: 10 May 2010

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The charge carrier density of the p-type doped organic semiconductor 2,7-bis(9-carbazolyl)-9,9-spirobifluorene is determined for varied doping concentrations. As p-type dopant molybdenum trioxide is used. We determine the carrier density by measuring the polaron induced optical absorption and by a capacitance-voltage analysis. We show that both results are in excellent agreement. An almost linear dependence of the charge carrier density on the doping concentration is observed. Carrier densities on the order of 1018 cm−3 at a dopant concentration of 1 mol % can be achieved. Overall, a low doping efficiency on the order of 2%–4.5% is evidenced.
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72.80.Le Polymers; organic compounds (including organic semiconductors)
81.05.Fb Organic semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
61.72.sd Impurity concentration
71.38.-k Polarons and electron-phonon interactions
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Charge generation layers comprising transition metal-oxide/organic interfaces: Electronic structure and charge generation mechanism

J. Meyer, M. Kröger, S. Hamwi, F. Gnam, T. Riedl, W. Kowalsky, and A. Kahn

Appl. Phys. Lett. 96, 193302 (2010); http://dx.doi.org/10.1063/1.3427430 (3 pages) | Cited 43 times

Online Publication Date: 10 May 2010

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The energetics of an archetype charge generation layer (CGL) architecture comprising of 4,4′,4″-tris(N-carbazolyl)triphenylamine (TCTA), tungsten oxide (WO3), and bathophenanthroline (BPhen) n-doped with cesium carbonate (Cs2CO3) are determined by ultraviolet and inverse photoemission spectroscopy. We show that the charge generation process occurs at the interface between the hole-transport material (TCTA) and WO3 and not, as commonly assumed, at the interface between WO3 and the n-doped electron-transport material (BPhen:Cs2CO3). However, the n-doped layer is also essential to the realization of an efficient CGL structure. The charge generation mechanism occurs via electron transfer from the TCTA highest occupied molecular orbital level to the transition metal-oxide conduction band.
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73.20.At Surface states, band structure, electron density of states
72.20.Fr Low-field transport and mobility; piezoresistance
79.60.Jv Interfaces; heterostructures; nanostructures
78.40.-q Absorption and reflection spectra: visible and ultraviolet
61.72.up Other materials
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Semicrystalline woodpile photonic crystals without complicated alignment via soft lithography

Jae-Hwang Lee, Ping Kuang, Wai Leung, Yong-Sung Kim, Joong-Mok Park, Henry Kang, Kristen Constant, and Kai-Ming Ho

Appl. Phys. Lett. 96, 193303 (2010); http://dx.doi.org/10.1063/1.3425756 (3 pages) | Cited 1 time

Online Publication Date: 13 May 2010

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We report the fabrication and characterization of woodpile photonic crystals with up to 12 layers through titania nanoparticle infiltration of a polymer template made by soft lithography. Because the complicated alignment in the conventional layer-by-layer fabrication associated with diamondlike symmetry is replaced by a simple 90° alignment, the fabricated photonic crystal has semicrystalline phase. However, the crystal performs similarly to a perfectly aligned crystal for the light propagation integrated from the surface normal to 30° at the main photonic band gap.
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42.70.Qs Photonic bandgap materials
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
81.16.Nd Micro- and nanolithography
81.07.Wx Nanopowders
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Spatial redistribution of the optical field intensity in inverted polymer solar cells

Fang-Chung Chen, Jyh-Lih Wu, and Yi Hung

Appl. Phys. Lett. 96, 193304 (2010); http://dx.doi.org/10.1063/1.3430060 (3 pages) | Cited 8 times

Online Publication Date: 14 May 2010

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We have used indium tin oxide (ITO), a transparent conducting oxide, as an optical spacer to improve the performance of inverted polymer solar cells. The optical interference effect resulted in spatial redistribution of the optical field in the devices. Although the degree of light absorption in inverted cells was not increased, the resulting favorable distribution of photogenerated excitons probably decreased the level of exciton quenching near the electrodes. As a result, the introduction of the ITO optical spacer at an appropriate thickness increased the short-circuit current density and the overall power conversion efficiency.
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88.40.jr Organic photovoltaics
88.40.H- Solar cells (photovoltaics)
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