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11 Feb 2008

Volume 92, Issue 6, Articles (06xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 92, 063101 (2008); http://dx.doi.org/10.1063/1.2839572 (3 pages)

M. N. Ou, T. J. Yang, S. R. Harutyunyan, Y. Y. Chen, C. D. Chen, and S. J. Lai
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Monolithic vertical microcavities based on tetracene single crystals

Pompilio Del Carro, Andrea Camposeo, Luana Persano, Silvia Tavazzi, Marcello Campione, Antonio Papagni, Luisa Raimondo, Leonardo Silvestri, Peter Spearman, Roberto Cingolani, and Dario Pisignano

Appl. Phys. Lett. 92, 063301 (2008); http://dx.doi.org/10.1063/1.2840153 (3 pages) | Cited 1 time

Online Publication Date: 11 February 2008

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The authors report on monolithic, light-emitting vertical microcavities based on an organic semiconductor single crystal. The devices are realized by reactive electron-beam deposition of dielectric mirrors and growth of tetracene crystals by physical vapor transport. The microcavities exhibit optical cavity modes in the visible range (550–580 nm) with full width at half maximum down to 2–3 nm, corresponding to a Q factor of about 200, and polarization-induced modal splitting up to 20 meV. These results open perspectives for the realization of polarized-emitting optoelectronic devices based on organic crystals.
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42.55.Px Semiconductor lasers; laser diodes
42.55.Sa Microcavity and microdisk lasers
42.60.By Design of specific laser systems
42.82.-m Integrated optics
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Anisotropic mobility in large grain size solution processed organic semiconductor thin films

R. L. Headrick, S. Wo, F. Sansoz, and J. E. Anthony

Appl. Phys. Lett. 92, 063302 (2008); http://dx.doi.org/10.1063/1.2839394 (3 pages) | Cited 9 times

Online Publication Date: 11 February 2008

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The hollow pen method for writing thin films of materials from solution is utilized to deposit films of 6,13-bis(tri-isopropylsilylethynyl) pentacene (TIPS pentacene) onto SiO2 surfaces with pre-patterned source/drain gold contacts. We demonstrate that large domains are obtained for TIPS pentacene films deposited from 0.5–4.0 wt % solutions with toluene. Crystalline grains with (001) orientation are observed to grow with sizes that can exceed 1 mm along the writing direction. A preferred azimuthal orientation is also selected by the process, resulting in anisotropic field effect transistor mobility in the films.
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68.55.ag Semiconductors
73.50.Dn Low-field transport and mobility; piezoresistance
72.20.Fr Low-field transport and mobility; piezoresistance
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High-efficiency and solution processible multilayer white polymer light-emitting diodes using neutral conjugated surfactant as an electron injection layer

Yong Zhang, Fei Huang, Alex K.-Y. Jen, and Yun Chi

Appl. Phys. Lett. 92, 063303 (2008); http://dx.doi.org/10.1063/1.2841637 (3 pages) | Cited 8 times

Online Publication Date: 11 February 2008

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High-efficiency white polymer light-emitting diodes were fabricated by using an yellow-emitting osmium complex Os(fptz)2(dppe) [fptz = 3-trifluoromethyl-5-(2-pyridyl)-1,2,4-triazole, dppe = cis-1,2-bis-(dipheneyl-phosphino) ethylene] doped into blue fluorescent copolymer based on an ultraviolet-blue light emitting host poly[2,7-(9,9-dioctylfluorene)-co-1,3-(5-carbazolphenylene)] and a blue light emitting component 4-N,N-diphenylaminostilbene (PFCz-DPS1-OXD5) as the emissive layer and a neutral conjugated surfactant, poly[9,9-bis(6′(diethanolamino)hexyl)-fluorene] (PFN-OH), as the electron injection layer sandwiched between the emissive layer and Al cathode. The device with the configuration of indium tin oxide/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid)/poly(N-vinylcarbazole)/Os(fptz)2(dppe)(1 wt %):PFCz-DPS1-OXD5/PFN-OH/Al exhibited efficient white light emission at the Commission Internationale de I’Eclairage coordinates of (0.33, 0.34) and a maximum luminance efficiency of 16.9 cd/A and brightness of 22100 cd/m2.
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85.60.Jb Light-emitting devices
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Laminated active matrix organic light-emitting devices

Hongyu Liu and Runguang Sun

Appl. Phys. Lett. 92, 063304 (2008); http://dx.doi.org/10.1063/1.2844854 (3 pages)

Online Publication Date: 13 February 2008

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Laminated active matrix organic light-emitting device (AMOLED) realizing top emission by using bottom-emitting organic light-emitting diode (OLED) structure was proposed. The multilayer structure of OLED deposited in the conventional sequence is not on the thin film transistor (TFT) backplane but on the OLED plane. The contact between the indium tin oxide (ITO) electrode of TFT backplane and metal cathode of OLED plane is implemented by using transfer electrode. The stringent pixel design for aperture ratio of the bottom-emitting AMOLED, as well as special technology for the top ITO electrode of top-emitting AMOLED, is unnecessary in the laminated AMOLED.
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85.60.Jb Light-emitting devices
85.30.Tv Field effect devices
82.45.Fk Electrodes
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Bias stress instability in pentacene thin film transistors: Contact resistance change and channel threshold voltage shift

S. D. Wang, T. Minari, T. Miyadera, Y. Aoyagi, and K. Tsukagoshi

Appl. Phys. Lett. 92, 063305 (2008); http://dx.doi.org/10.1063/1.2844857 (3 pages) | Cited 26 times

Online Publication Date: 13 February 2008

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Bias stress instability in top-contact pentacene thin film transistors was observed to be correlated not only to the channel but also to the metal/organic contact. The drain current decay under bias stress results from the combination of the contact resistance change and the threshold voltage shift in the channel. The contact resistance change is contact-metal dependent, though the corresponding channel threshold voltage shifts are similar. The results suggest that the time-dependent charge trapping into the deep trap states in both the contact and channel regions is responsible for the bias stress effect in organic thin film transistors.
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85.30.Tv Field effect devices
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Suppression of exciton annihilation at high current densities in organic light-emitting diode resulting from energy-level alignments of carrier transport layers

Toshinori Matsushima and Chihaya Adachi

Appl. Phys. Lett. 92, 063306 (2008); http://dx.doi.org/10.1063/1.2844891 (3 pages) | Cited 7 times

Online Publication Date: 14 February 2008

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We manufactured an organic light-emitting diode (OLED) in which the hole and electron transport layers are chemically doped with p- and n-type dopants and energy levels in between neighboring carrier transport layers and emitting molecules are aligned. From the results of the electroluminescence (EL) characteristics of the OLED, we found that (1) the OLED has an extremely low driving voltage of 2.65±0.05 0.05 V at a current density of 100 mA/cm2; (2) the onset voltage of EL ( ≈ 2.4 V) corresponds to the photon energy of emitting molecules ( ≈ 2.5 eV), while the onset voltage of currents is ≈ 1.8 V; and (3) a decrease in EL efficiency at high current densities can be suppressed by matching the energy levels.
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85.60.Jb Light-emitting devices
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High work function materials for source/drain contacts in printed polymer thin film transistors

V. Sholin, S. A. Carter, R. A. Street, and A. C. Arias

Appl. Phys. Lett. 92, 063307 (2008); http://dx.doi.org/10.1063/1.2857461 (3 pages) | Cited 4 times

Online Publication Date: 14 February 2008

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Studies of materials for source-drain electrodes in ink-jet printed polymer-based thin film transistors (TFTs) are reported. Two systems are studied: a blend of Ag nanoparticles with poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) and an ethylene glycol-doped PEDOT:PSS solution (modified-PEDOT). The semiconductor used is the polythiophene derivative poly [5,5′-bis(3-dodecyl-2-thienyl)-2,2,2′-bithiophene]. PEDOT:Ag blends and modified-PEDOT yield TFTs with mobilities around 10−2 and 10−3 cm2/V s, respectively, subthreshold slopes around 1.6 V/decade and on-to-off current ratios of 106–107. Both systems show considerable improvement over printed TFTs with Ag nanoparticle source-drain electrodes. Results on film resistivity and morphology are discussed along with device characteristic analysis.
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85.30.Tv Field effect devices
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Molecular orientation dependent interfacial dipole at the F16CuPc/CuPc organic heterojunction interface

Wei Chen, Shi Chen, Han Huang, Dong Chen Qi, Xing Yu. Gao, and Andrew Thye Shen Wee

Appl. Phys. Lett. 92, 063308 (2008); http://dx.doi.org/10.1063/1.2857460 (3 pages) | Cited 31 times

Online Publication Date: 15 February 2008

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In situ synchrotron-based near-edge x-ray absorption fine structure measurements and photoemission spectroscopy have been used to investigate the effect of molecular orientation on the interfacial dipole and the energy level alignment at the interfaces of organic heterojunctions comprising copper-hexadecafluoro-phthalocyanine (F16CuPc) on both standing-up and lying-down copper(II) phthalocyanine (CuPc) thin films. It is found that F16CuPc thin films adopt the same molecular orientation of the underlying CuPc thin films. An interfacial dipole of 0.45 eV forms at the interface of lying-down F16CuPc/CuPc on highly ordered pyrolytic graphite. In contrast, a much larger interfacial dipole of 1.35 eV appears at the interface of standing-up F16CuPc/CuPc on octane-1-thiol terminated Au(111).
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78.70.Dm X-ray absorption spectra
79.60.Jv Interfaces; heterostructures; nanostructures
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
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Two-photon energy transfer enhanced three-dimensional optical memory in quantum-dot and azo-dye doped polymers

Xiangping Li, James W. M. Chon, Richard A. Evans, and Min Gu

Appl. Phys. Lett. 92, 063309 (2008); http://dx.doi.org/10.1063/1.2857497 (3 pages) | Cited 11 times

Online Publication Date: 15 February 2008

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A three-dimensional bit-by-bit optical memory system in quantum-dot and azo-dye doped polymers is demonstrated in this paper. It is shown that two-photon absorption can be used to excite resonance energy transfer from luminescent CdS quantum dots to azo-dye molecules. As a result, the isomerization of azo-dye molecules leads to a pronounced refractive index change. This two-photon-excited energy transfer process in the quantum-dot and azo-dye polymer not only allows for high efficient multilayer information recording into the volume of thick samples but also offers a refractive index window for readout.
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42.79.Vb Optical storage systems, optical disks
42.70.Jk Polymers and organics
78.67.Hc Quantum dots
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
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High performance polythiophene thin-film transistors doped with very small amounts of an electron acceptor

Liang Ma, Wi Hyoung Lee, Yeong Don Park, Jong Soo Kim, Hwa Sung Lee, and Kilwon Cho

Appl. Phys. Lett. 92, 063310 (2008); http://dx.doi.org/10.1063/1.2883927 (3 pages) | Cited 8 times

Online Publication Date: 15 February 2008

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The relationship between the electrical properties and the microstructure of poly(3-hexylthiophene) (P3HT) films doped with an electron acceptor, 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) has been studied. The introduction of F4-TCNQ in very small quantities improved the device performance of P3HT thin-film transistors significantly. The field-effect mobility of a device doped with only 0.2 wt % F4-TCNQ was enhanced by a factor of 30 with respect to that of a pure P3HT device. The threshold voltages of the P3HT thin-film transistors can also be controlled by adjusting the F4-TCNQ concentration. These improvements are attributed to the doping-induced formation of charge-transfer complexes and improved molecular orientation of the P3HT.
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85.30.Tv Field effect devices
73.61.Ph Polymers; organic compounds
61.41.+e Polymers, elastomers, and plastics
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
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