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13 Sep 2010

Volume 97, Issue 11, Articles (11xxxx)

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Appl. Phys. Lett. 97, 113701 (2010); http://dx.doi.org/10.1063/1.3487998 (3 pages)

Sarah E. Baker, Michael D. Pocha, Allan S. P. Chang, Donald J. Sirbuly, Stefano Cabrini, Scott D. Dhuey, Tiziana C. Bond, and Sonia E. Létant
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Transient electroluminescence dynamics in small molecular organic light-emitting diodes

Zhengqing Gan, Rui Liu, Ruth Shinar, and Joseph Shinar

Appl. Phys. Lett. 97, 113301 (2010); http://dx.doi.org/10.1063/1.3481687 (3 pages) | Cited 5 times

Online Publication Date: 14 September 2010

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Intriguing electroluminescence (EL) spikes, following a voltage pulse applied to small molecular OLEDs, are discussed, elucidating carrier and exciton quenching dynamics and their relation to device structure. At low temperatures, all devices exhibit spikes at ∼ 70–300 ns and μs-long tails. At 295 K only those with a hole injection barrier, carrier-trapping guest-host emitting layer, and no strong hole-blocking layer exhibit the spikes. They narrow and appear earlier under post-pulse reverse bias. The spikes and tails are in agreement with a revised model of recombination of correlated charge pairs (CCPs) and initially unpaired charges. Decreased post-pulse field-induced dissociative quenching of singlet excitons and CCPs, and possibly increased post-pulse current of holes that “turn back” toward the recombination zone after having drifted beyond it are suspected to cause the spikes’ amplitude, which exceeds the dc EL.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
71.35.-y Excitons and related phenomena
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Charge modulated reflectance topography for probing in-plane carrier distribution in pentacene field-effect transistors

Takaaki Manaka, Satoshi Kawashima, and Mitsumasa Iwamoto

Appl. Phys. Lett. 97, 113302 (2010); http://dx.doi.org/10.1063/1.3490716 (3 pages) | Cited 9 times

Online Publication Date: 16 September 2010

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By using charge modulated reflectance (CMR) topography, we showed that the in-plane carrier distribution in pentacene field-effect transistors (FETs) can be directly probed under the device operation. Further, we showed that the observed CMR signal is attributed to a decrease in the electron population in pentacene highest occupied molecular orbital level, caused by hole injection. The signal profile along the FET channel strongly depends on the bias conditions. The carrier density decreases monotonously along the channel from the source to the drain in the saturated region; this decrease is interpreted by a simple model based on interfacial accumulated charge transportation.
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85.30.Tv Field effect devices
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Measurement of nanoscale external quantum efficiency of conjugated polymer:fullerene solar cells by photoconductive atomic force microscopy

Xuan-Dung Dang, Alexander Mikhailovsky, and Thuc-Quyen Nguyen

Appl. Phys. Lett. 97, 113303 (2010); http://dx.doi.org/10.1063/1.3483613 (3 pages) | Cited 6 times

Online Publication Date: 17 September 2010

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Photoconductive atomic force microscopy is used to investigate nanoscale incident photon-to-current efficiency spectra of polymer bulk heterojunction solar cells based on poly[2-methoxy-5-(3,7-dimethyloctyloxy)]-1,4-phenylenevinylene (MDMO-PPV) and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM). Nanoscale external quantum efficiency reveals the complex morphology of MDMO-PPV:PC71BM films cast from toluene solution. Not only electron transfer from the photoexcited donor to the fullerene but also hole transfer process from photoexcited fullerene to the donor phase due to highest occupied molecular orbital offset is observed. The difference in performance between toluene and chlorobenzene-cast devices is explained by the variation in relative contributions from two charge transfer mechanisms.
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61.48.-c Structure of fullerenes and related hollow and planar molecular structures
68.35.bp Fullerenes
81.05.ub Fullerenes and related materials
88.40.J- Types of solar cells
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