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15 Aug 2011

Volume 99, Issue 7, Articles (07xxxx)

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Appl. Phys. Lett. 99, 073701 (2011); http://dx.doi.org/10.1063/1.3599706 (3 pages)

Miguel A. Santiago-Cordoba, Svetlana V. Boriskina, Frank Vollmer, and Melik C. Demirel
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The immobilization and electrical response of single-stranded DNA molecules on pentacene transistors

Qingping Zhu, Feifei Xing, Changhe Liu, Yulei Hu, Na Liu, and Jun Wang

Appl. Phys. Lett. 99, 073301 (2011); http://dx.doi.org/10.1063/1.3623438 (3 pages) | Cited 3 times

Online Publication Date: 16 August 2011

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The immobilization and electrical response of single-stranded deoxyribonucleic acid (ssDNA) on pentacene-based transistors have been studied. The result displays that ssDNA molecules may be well immobilized onto pentacene film surface observed by atomic force microscopy. The device parameters of transistors including drain-source current and threshold voltage exhibit an obvious change by comparing with pristine transistors that can be attributed to the additional positive charges induced by immobilized ssDNA molecules. Furthermore, the dependence of electrical response on the ssDNA solution concentration was disclosed.
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85.30.Tv Field effect devices
85.65.+h Molecular electronic devices
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Electrical dipole-dipole interaction effects on magnetocurrent in organic phosphorescent materials

Ming Shao, Yanfeng Dai, Dongge Ma, and Bin Hu

Appl. Phys. Lett. 99, 073302 (2011); http://dx.doi.org/10.1063/1.3623435 (3 pages) | Cited 2 times

Online Publication Date: 17 August 2011

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This letter reports the experimental studies on electrical dipole-dipole interaction effects on magnetocurrent (MC) and magneto-electroluminescence (MFEEL) based on two phosphorescent dyes: heavy-metal complex Ir(ppy)3 and Ir(ppy)2(acac) with strong spin-orbital coupling but different electrical dipole moments. We find that the Ir(ppy)3 with strong electrical dipole moment shows negligible MC and MFEEL. However, the Ir(ppy)2(acac) with weak dipole moment exhibits appreciable MC and MFEEL. The experimental results suggest that the electrical dipole-dipole interaction can change the MC and MFEEL from capture-based regime, where charge carriers are captured through spin-dependent process at short distance, to intersystem crossing-based regime, where charge carriers are captured through spin random process at long distance. As a result, changing electrical dipole-dipole interaction presents a new pathway to tune magnetic field effects in organic semiconductors.
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78.60.Fi Electroluminescence
75.30.Cr Saturation moments and magnetic susceptibilities
78.55.Kz Solid organic materials
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Highly efficient bi-directional organic light-emitting diodes by strong micro-cavity effects

Jonghee Lee, Simone Hofmann, Michael Thomschke, Mauro Furno, Yong Hyun Kim, Björn Lüssem, and Karl Leo

Appl. Phys. Lett. 99, 073303 (2011); http://dx.doi.org/10.1063/1.3628292 (3 pages) | Cited 3 times

Online Publication Date: 17 August 2011

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We report on highly enhanced light outcoupling of bi-directional red phosphorescent organic light-emitting diodes (BiOLEDs) by strong micro-cavity effects. Inserting additional metal layers between the indium tin oxide (ITO) anode and the hole transporting layer (HTL) and controlling the thickness of the counter metal electrode result in dramatic changes in electroluminescence spectra and angular distribution. We find that the external quantum efficiency (EQE) for both bottom and top emitting side can be significantly improved: the overall EQE reaches up to 24.24%.
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85.60.Jb Light-emitting devices
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Charge balance and photon collection in polymer based ternary bulk heterojunction photovoltaic devices containing cadmium selenide nanoparticles

Eric D. Peterson, Gregory M. Smith, Minglai Fu, Richard D. Adams, Robert C. Coffin, and David L. Carroll

Appl. Phys. Lett. 99, 073304 (2011); http://dx.doi.org/10.1063/1.3627165 (3 pages) | Cited 1 time

Online Publication Date: 18 August 2011

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Solar cells employing a ternary bulk heterojunction active layer comprised of poly(3-hexylthiophene) (P3HT), 6,6-phenyl C61-butyric acid methyl ester (PCBM) doped with composites constructed from a combination of 2.5 nm CdSe nanoparticles (NP), and methyl viologen (MV) have been examined. It was found that the devices containing the CdSe NP/MV composite exhibit significantly more photocurrent in a region surrounding the absorption peak of the particles (560-660 nm) when compared to pristine P3HT:PCBM devices. For a low ratio of CdSe to PCBM, the photocurrent collection was accompanied by space charge build up that limited the performance of the devices. When the ratio of CdSe to PCBM was raised, the space charge dissipated and performance recovered. JV curve shape analysis suggests that charge balance was achieved; however, electrode selectivity was reduced.
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61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
81.07.Bc Nanocrystalline materials
61.41.+e Polymers, elastomers, and plastics
81.05.Fb Organic semiconductors
81.05.Dz II-VI semiconductors
79.60.-i Photoemission and photoelectron spectra
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Interface state and dipole assisted hole injection improvement with 1,4,5,8,-naphthalene-tetracarboxylic-dianhydride in organic light-emitting devices

Pyungeun Jeon, Hyunbok Lee, Jeihyun Lee, Kwangho Jeong, JinWoo Lee, and Yeonjin Yi

Appl. Phys. Lett. 99, 073305 (2011); http://dx.doi.org/10.1063/1.3628293 (3 pages) | Cited 3 times

Online Publication Date: 18 August 2011

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1,4,5,8-naphthalene-tetracarboxylic-dianhydride (NTCDA) is known to improve hole injection when inserted between the hole transport layer and the indium tin oxide (ITO) anode in organic light emitting devices. To clarify the origin of the improvement, the interfacial electronic structures between N,N′-diphenyl-N, N′-bis(1-naphthyl)(1,1′-biphenyl)-4,4′ diamine (NPB, typical hole transport layer) and ITO with a NTCDA insertion layer were explored. The NTCDA layer generates an interface state when it interacts with ITO and also induces large interface dipole. The interface state assists hole transport and the interface dipole pulls entire energy levels of NPB up, reducing the hole injection barrier.
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85.60.Jb Light-emitting devices
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Charge carrier extraction dynamics for organic field effect transistor structures

Hsiu-Chuang Chang, P. Paul Ruden, Yan Liang, and C. Daniel Frisbie

Appl. Phys. Lett. 99, 073306 (2011); http://dx.doi.org/10.1063/1.3625945 (3 pages) | Cited 1 time

Online Publication Date: 18 August 2011

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We present experimental data and a model for charge carrier extraction from the channel of a device structure resembling an organic field effect transistor. The initially accumulated channel is depleted by a sudden change of the gate voltage. The measured discharge current transient decreases either as a power law or exponentially if the final state of the channel is completely or partially depleted, respectively. The extraction process is modeled with a capacitor/resistor circuit with a time-dependent resistance that increases with decreasing channel carrier density. Analytical and numerical results are discussed and compared with the experimental data.
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85.30.Tv Field effect devices
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Magnetoconductance responses in organic charge-transfer-complex molecules

Tsung-Hsun Lee, Jhen-Hao Li, Wei-Shun Huang, Bin Hu, J. C. A. Huang, Tzung-Fang Guo, and Ten-Chin Wen

Appl. Phys. Lett. 99, 073307 (2011); http://dx.doi.org/10.1063/1.3627170 (3 pages) | Cited 4 times

Online Publication Date: 19 August 2011

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Blending 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ), a high electron affinity organic molecule, with N,N′-bis-(1-naphyl)-N,N′-diphenyl-1,1′-biphenyl′-4,4′-diamine (NPB) creates the charge-transfer-complex molecules and modulates the magnetoconductance (MC) responses of devices by an applied electrical bias. A negative MC response (−0.60%) is observed for the device made of NPB:F4-TCNQ(30%) film as the active layer, which has a distinct characteristic to negligible MC responses in pristine NPB- and F4-TCNQ-based devices. We attribute the MC responses to the magnetic-field-dependent transport of injected charge carriers through charge-transfer-complex molecules in the NPB:F4-TCNQ system, which are varied with the F4-TCNQ blending concentrations and the injection of minority charge carriers. Results of this study demonstrate a turning point of MC responses at the bias voltage near the threshold of the bipolar injection.
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72.20.My Galvanomagnetic and other magnetotransport effects
75.47.Pq Other materials
73.61.Ph Polymers; organic compounds
81.05.Fb Organic semiconductors
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Effect of electron transport layer crystallinity on the transient characteristics of inverted organic solar cells

Yong-Jin Kang, Chang Su Kim, Dae Sung You, Sung Hoon Jung, Kyounga Lim, Do-Geun Kim, Jong-Kuk Kim, Soo Hyung Kim, Yu-Ri Shin, Se-Hun Kwon, and Jae-Wook Kang

Appl. Phys. Lett. 99, 073308 (2011); http://dx.doi.org/10.1063/1.3628319 (3 pages) | Cited 3 times

Online Publication Date: 19 August 2011

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We present how the crystallinity of the electron transport layer can dramatically influence the transient characteristics of organic solar cells. We employed an inverted cell structure using TiOx prepared by atomic layer deposition as an electron transport layer. The device possessing the amorphous phase TiOx exhibited a continuous increase in the device characteristics upon continuous illumination at ambient, which is attributed to the filling of shallow electron traps within the amorphous phase TiOx upon illumination. In contrast, the characteristics of the device with the crystalline phase TiOx showed a negligible increase upon continuous illumination.
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88.40.jr Organic photovoltaics
88.40.hj Efficiency and performance of solar cells
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