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21 May 2012

Volume 100, Issue 21, Articles (21xxxx)

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Appl. Phys. Lett. 100, 213701 (2012); http://dx.doi.org/10.1063/1.3701135 (4 pages)

Wen Lo, Ara Ghazaryan, Chien-Hsin Tso, Po-Sheng Hu, Wei-Liang Chen, Tsung-Rong Kuo, Sung-Jan Lin, Shean-Jen Chen, Chia-Chun Chen, and Chen-Yuan Dong
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High efficiency blue phosphorescent organic light-emitting diode based on blend of hole- and electron-transporting materials as a co-host

Yonghua Chen, Jiangshan Chen, Yongbiao Zhao, and Dongge Ma

Appl. Phys. Lett. 100, 213301 (2012); http://dx.doi.org/10.1063/1.4720512 (4 pages) | Cited 4 times

Online Publication Date: 21 May 2012

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Highly efficient blue phosphorescent organic light-emitting diodes (PHOLEDs) were achieved by blending the same hole- and electron-transporting layer materials in device as the host in the emissive layer. The design of this kind of device structure not only decreases the amount of used organic materials but also greatly reduces the structural heterogeneities and effectively facilitates the charge injection into the emissive layer. The resulting blue PHOLEDs exhibit higher electroluminescent efficiency. The maximum external quantum efficiency and power efficiency reach 20.4% and 55.4 lm W−1, respectively, yet keep 19.5% and 49.9 lm W−1, 18.3% and 40.9 lm W−1, respectively, at a luminance of 100 and 1000 cd m−2, showing a low efficiency roll-off property. The mechanism studies fully demonstrate that the bipolar co-host system extends the lifetime of excitons, broadens the recombination zone, and improves the charge carrier injection and transport balance, which are of greatly critical to get the improved efficiency and efficiency roll-off at high luminance in the blue PHOLEDs.
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85.60.Jb Light-emitting devices
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Transparent conductive electrodes of mixed TiO2−x–indium tin oxide for organic photovoltaics

Kyu-Sung Lee, Jong-Wook Lim, Han-Ki Kim, T. L. Alford, and Ghassan E. Jabbour

Appl. Phys. Lett. 100, 213302 (2012); http://dx.doi.org/10.1063/1.4707381 (3 pages) | Cited 2 times

Online Publication Date: 22 May 2012

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A transparent conductive electrode of mixed titanium dioxide (TiO2−x)–indium tin oxide (ITO) with an overall reduction in the use of indium metal is demonstrated. When used in organic photovoltaic devices based on bulk heterojunction photoactive layer of poly (3-hexylthiophene) and [6,6]-phenyl C61 butyric acid methyl ester, a power conversion efficiency of 3.67% was obtained, a value comparable to devices having sputtered ITO electrode. Surface roughness and optical efficiency are improved when using the mixed TiO2−x–ITO electrode. The consumption of less indium allows for lower fabrication cost of such mixed thin film electrode.
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84.60.Jt Photoelectric conversion
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Nonvolatile organic write-once-read-many-times memory devices based on hexadecafluoro-copper-phthalocyanine

Lidan Wang, Zisheng Su, and Cheng Wang

Appl. Phys. Lett. 100, 213303 (2012); http://dx.doi.org/10.1063/1.4721518 (4 pages) | Cited 2 times

Online Publication Date: 22 May 2012

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Nonvolatile organic write-once-read-many-times memory device was demonstrated based on hexadecafluoro-copper-phthalocyanine (F16CuPc) single layer sandwiched between indium tin oxide (ITO) anode and Al cathode. The as fabricated device remains in ON state and it can be tuned to OFF state by applying a reverse bias. The ON/OFF current ratio of the device can reach up to 2.3 × 103. Simultaneously, the device shows long-term storage stability and long retention time in air. The ON/OFF transition is attributed to the formation and destruction of the interfacial dipole layer in the ITO/F16CuPc interface, and such a mechanism is different from previously reported ones.
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84.30.Sk Pulse and digital circuits
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Optically pumped lasing from organic two-dimensional planar photonic crystal microcavity

F. Gourdon, M. Chakaroun, N. Fabre, J. Solard, E. Cambril, A.-M. Yacomotti, S. Bouchoule, A. Fischer, and A. Boudrioua

Appl. Phys. Lett. 100, 213304 (2012); http://dx.doi.org/10.1063/1.4720178 (4 pages) | Cited 1 time

Online Publication Date: 23 May 2012

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In this letter, we report the realization and characterization of a planar two-dimensional organic photonic crystal microcavity laser. The gain medium consists of a tris(8-hydroxyquinolinato) aluminum doped with 4-(dicyanomethylene)-2-t-butyl-6(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran and is deposited on a lithographically patterned silicon nitride two dimensional photonic crystal H2 microcavity. The experimental results show a laser emission at 662 nm with a threshold of 9.7 μJ/cm2.
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42.55.Px Semiconductor lasers; laser diodes
42.82.Gw Other integrated-optical elements and systems
42.70.Qs Photonic bandgap materials
42.55.Tv Photonic crystal lasers and coherent effects
42.55.Sa Microcavity and microdisk lasers
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
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Biased internal potential distributions in a bulk-heterojunction organic solar cell incorporated with a TiOx interlayer

Jaemin Kong, Jongjin Lee, Yonkil Jeong, Maengjun Kim, Sung-Oong Kang, and Kwanghee Lee

Appl. Phys. Lett. 100, 213305 (2012); http://dx.doi.org/10.1063/1.4722802 (3 pages) | Cited 1 time

Online Publication Date: 24 May 2012

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External-biased potential distributions of a polymer bulk-heterojunction (BHJ) solar cell, incorporated with electron/hole transporting layers, were directly obseved through a cross-sectional Kelvin probe force microscopy. The bulk electric field of BHJ was found to be nearly field-free even under reverse biases, and the field-free region was probed to expand with the incorporation of TiOx electron transporting layer; as a result, inducing a decrease of quasi-Fermi level splitting region in obtaining a high fill factor in the TiOx-interlayered junction photodiodes.
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88.40.H- Solar cells (photovoltaics)
85.60.Dw Photodiodes; phototransistors; photoresistors
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Photophysics and morphology of poly (3-dodecylthienylenevinylene)-[6,6]–phenyl-C61-butyric acid methyl ester composite

E. Lafalce, P. Toglia, C. Zhang, and X. Jiang

Appl. Phys. Lett. 100, 213306 (2012); http://dx.doi.org/10.1063/1.4720091 (5 pages)

Online Publication Date: 25 May 2012

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A series of low band gap poly(3-dodecylthienylenevinylene) (PTV) with controlled morphological order have been synthesized and blended with the electron acceptor [6,6]–phenyl-C61-butyric acid methyl ester (PCBM) for organic photovoltaic devices. Two polymers with the most and least side chain regioregularity were chosen in this work, namely the PTV010 and PTV55, respectively. Using photoluminescence, photo-induced absorption spectroscopy, and atomic force microscopy, we find no direct evidence of photoinduced charge transfer between the two constituents, independent of the bulk-heterojunction morphology of the film, although the possibility of formation of P+/C60− charge transfer complex was not completely ruled out. The large exciton binding energy (Eb = 0.6 eV) in PTV inhibits the photoinduced electron transfer from PTV to PCBM. In addition, excitons formed on polymer chains suffer ultrafast (<ps) intrachain decay to the dark 2Ag state in both PTV010 and PTV55 cases, whereas excitons generated on PCBM molecules undergo energy transfer only to PTV55 in the blend film. Thus, the addition of PCBM increases the photoluminescence yield with respect to neat polymer yield. The efficiency of the energy transfer process is shown to depend on the degree of polymer and PCBM intermixing within the film, which in turn is governed by the polymer chain orders. The effect of such intermixing on the resulting kinetics of photo-induced excitations is also discussed. Our results show limited effect of polymer crystallinity of PTV to its excitonic properties, much the contrary of the case with poly (3-hexylthiophene) which has similar chemical structure with PTV.
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78.66.Sq Composite materials
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
68.35.B- Structure of clean surfaces (and surface reconstruction)
71.20.-b Electron density of states and band structure of crystalline solids
71.35.-y Excitons and related phenomena
78.55.-m Photoluminescence, properties and materials
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