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11 Feb 2013

Volume 102, Issue 6, Articles (06xxxx)

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Appl. Phys. Lett. 102, 063701 (2013); http://dx.doi.org/10.1063/1.4790115 (5 pages)

In-Tsang Lin, Hong-Chang Yang, and Jyh-Horng Chen
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Identifying the efficient inter-conversion between singlet and triplet charge-transfer states by magneto-electroluminescence study

Ping Chen, Qiming Peng, Liang Yao, Na Gao, and Feng Li

Appl. Phys. Lett. 102, 063301 (2013); http://dx.doi.org/10.1063/1.4791562 (4 pages) | Cited 1 time

Online Publication Date: 11 February 2013

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Using the magneto-electroluminescence (MEL) as a tool, we demonstrated the efficient inter-conversion between singlet and triplet charge-transfer (CT) states in exciplex-based organic light-emitting diodes (OLEDs). Results show that the MEL of exciplex-based device is larger than that of exciton-based device by a factor of 3.2. The emission of exciplex-based devices comes from the direct intermolecular electron-hole pair recombination and their spin exchange energy is much smaller, which causes the efficient inter-conversion between singlet and triplet states. This argument was supported by the consistent evolutions of the MEL and EL spectra versus applied bias and donor concentrations. Finally, the bandgap effects on the MEL as well as the external quantum efficiency of exciplex-based devices were discussed. Our findings of MEL may offer a feasible way to unravel underlying mechanisms that limit the EL efficiency in the OLEDs.
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85.60.Jb Light-emitting devices
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Study of the fast photoswitching of spin crossover nanoparticles outside and inside their thermal hysteresis loop

G. Gallé, C. Etrillard, J. Degert, F. Guillaume, J.-F. Létard, and E. Freysz

Appl. Phys. Lett. 102, 063302 (2013); http://dx.doi.org/10.1063/1.4792527 (4 pages)

Online Publication Date: 13 February 2013

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We have studied the low spin to high spin phase transition induced by nanosecond laser pulses outside and within the thermal hysteresis loop of the [Fe(Htrz)2 trz](BF4)2-H2O spin crossover nanoparticles. We demonstrate that, whatever the temperature of the compound, the photo-switching is achieved in less than 12.5 ns. Outside the hysteresis loop, the photo-induced high spin state remains up to 100 μs and then relaxes. Within the thermal hysteresis loop, the photo-induced high spin state remains as long as the temperature of the sample is kept within the thermal loop. A Raman study indicates that the photo-switching can be completed using single laser pulse excitation.
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42.65.Pc Optical bistability, multistability, and switching, including local field effects
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
78.30.-j Infrared and Raman spectra
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Electronic and interface properties of polyfluorene films on GaN for hybrid optoelectronic applications

G. Itskos, X. Xristodoulou, E. Iliopoulos, S. Ladas, S. Kennou, M. Neophytou, and S. Choulis

Appl. Phys. Lett. 102, 063303 (2013); http://dx.doi.org/10.1063/1.4792211 (5 pages)

Online Publication Date: 13 February 2013

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Electronic and interface properties of spin-coated poly(9,9-dioctylfluorenyl-2,7-diyl) (PFO) films on GaN have been investigated in terms of their potential for optoelectronic applications. The PFO/GaN interface was studied by photoemission spectroscopy showing a type-II energy alignment with band offsets suitable for efficient photocurrent generation. The light harvesting potential is further supported by fluorescence experiments that show evidence of photo-induced electron transfer from PFO to GaN. The impact of polymer film thickness was probed using emission anisotropy and ellipsometry, indicating the presence of an ordered planar phase of PFO. The study has implications to hybrid optoelectronic devices employing the two important materials.
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85.60.Bt Optoelectronic device characterization, design, and modeling
73.20.At Surface states, band structure, electron density of states
78.55.-m Photoluminescence, properties and materials
78.66.-w Optical properties of specific thin films
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Cadmium-free copper indium gallium diselenide hybrid solar cells comprising a 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole buffer layer

Manuel Reinhard, Christoph Simon, Johannes Kuhn, Linda Bürkert, Marco Cemernjak, Bernhard Dimmler, Uli Lemmer, and Alexander Colsmann

Appl. Phys. Lett. 102, 063304 (2013); http://dx.doi.org/10.1063/1.4792507 (4 pages)

Online Publication Date: 14 February 2013

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Copper indium gallium diselenide (CIGS) solar cells are the most efficient thin film photovoltaic devices today. In this work, we investigate CIGS/organic hybrid solar cells comprising a semi-transparent metal top electrode and a wide band gap organic semiconductor as buffer layer. Depositing the organic semiconductor from solution, we fabricate Cd-free solar cells exhibiting about the same efficiency as their counterparts comprising CdS and significantly higher open-circuit voltages as compared to buffer-free devices. Although the organic molecules do not cover the CIGS surface homogeneously, their use enables prolonged charge carrier lifetimes according to impedance spectroscopy measurements.
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88.40.jn Thin film Cu-based I-III-VI2 solar cells
88.40.jr Organic photovoltaics
88.40.hj Efficiency and performance of solar cells
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Self-contact thin-film organic transistors based on tetramethyltetrathiafulvalene

Sumika Tamura, Tomofumi Kadoya, Tadashi Kawamoto, and Takehiko Mori

Appl. Phys. Lett. 102, 063305 (2013); http://dx.doi.org/10.1063/1.4792704 (4 pages)

Online Publication Date: 14 February 2013

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Carrier injection from organic contacts to tetramethyltetrathiafulvalene (TMTTF) is investigated in the thin-film transistors. When 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) is patterned on a TMTTF film, the resulting (TMTTF)(TCNQ) works as highly conducting source and drain electrodes. Such self-contact transistors, in which the organic material constructing the active layer is selectively transformed to the contacts, have achieved low contact resistance and high performance.
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85.30.Tv Field effect devices
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Real-time dynamic hologram in photorefractive ferroelectric liquid crystal with two-beam coupling gain coefficient of over 800 cm–1 and response time of 8 ms

Takeo Sasaki, Masashi Ikegami, Tatsuya Abe, Daisuke Miyazaki, Satoshi Kajikawa, and Yumiko Naka

Appl. Phys. Lett. 102, 063306 (2013); http://dx.doi.org/10.1063/1.4792735 (4 pages) | Cited 1 time

Online Publication Date: 14 February 2013

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The photorefractive effect in photoconductive ferroelectric liquid crystals (FLCs) that contain photoconductive chiral compounds was investigated. Terthiophene compounds with chiral structure were chosen as the photoconductive chiral compounds and mixed with an achiral smectic C liquid crystal. The mixture exhibited the ferroelectric chiral smectic C phase and photoconductivity. The photorefractivity of the mixture was investigated by two-beam coupling experiment. It was found that the FLC containing the photoconductive chiral compound exhibits a large gain coefficient of over 800 cm−1 and a fast response time of 8 ms. The high photorefractive performance was considered to be due to enhanced charge mobility.
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42.40.-i Holography
42.70.Df Liquid crystals
42.70.Gi Light-sensitive materials
42.70.Ln Holographic recording materials; optical storage media
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