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20 Feb 2012

Volume 100, Issue 8, Articles (08xxxx)

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Appl. Phys. Lett. 100, 082401 (2012); http://dx.doi.org/10.1063/1.3684972 (4 pages)

Elizabeth Rapoport and Geoffrey S. D. Beach
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High efficiency organic solar cells with spray coated active layers comprised of a low band gap conjugated polymer

Wanyi Nie, Robert C. Coffin, Jiwen Liu, Yuan Li, Eric D. Peterson, Christopher M. MacNeill, Ronald E. Noftle, and David L. Carroll

Appl. Phys. Lett. 100, 083301 (2012); http://dx.doi.org/10.1063/1.3687911 (4 pages) | Cited 5 times

Online Publication Date: 22 February 2012

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Airbrush is a promising tool for large scale organic thin film deposition in photovoltaic devices fabrication. This paper reports a detailed study on solar cell performance using airbrush spray deposition for active layer composed with recently developed low band gap donor material poly[4,8-bis(1-pentylhexyloxy)benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl-alt-2,1,3-benzoxadiazole-4,7-diyl and [6,6]-phenyl-C61-butyric acid methyl ester. The effect of carrier solvent and substrate temperature on film morphology are studied; a formula in 1,2-dichlorobenzene sprayed at a substrate temperature of 80 °C is found to be the optimum condition that produces a peak power conversion efficiency of 5.8%.
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88.40.jr Organic photovoltaics
88.40.hj Efficiency and performance of solar cells
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Enhanced electrical stability of organic thin-film transistors with polymer semiconductor-insulator blended active layers

Jiyoul Lee, Ji Young Jung, Do Hwan Kim, Joo-Young Kim, Bang-Lin Lee, Jeong-Il Park, Jong Won Chung, Joon Seok Park, Bonwon Koo, Yong Wan Jin, and Sangyoon Lee

Appl. Phys. Lett. 100, 083302 (2012); http://dx.doi.org/10.1063/1.3688177 (5 pages) | Cited 4 times

Online Publication Date: 22 February 2012

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We report on an enhanced electrical stability of organic thin-film transistors (OTFTs), where an organic semiconductor (poly(didodecylquaterthiophene-alt-didodecylbithiazole) (PQTBTz-C12)) and a polymer insulator (poly(methyl methacrylate) (PMMA)) blended film were used as the active layer, in comparison with a single PQTBTz-C12 OTFT. While both devices exhibit similar electrical performance in terms of mobility and ON/OFF ratios, the blended device is less susceptible to OFF-bias stress. It is suggested that the carboxyl groups of PMMA in the blend may act as suppressors with regards to hole accumulation in the channel, and thus, the PQTBTz-C12/PMMA blend based OTFTs exhibit delayed threshold voltage shifts under OFF-bias stress.
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85.30.Tv Field effect devices
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Characterizing the charge collection efficiency in bulk heterojunction organic photovoltaic cells

Richa Pandey and Russell J. Holmes

Appl. Phys. Lett. 100, 083303 (2012); http://dx.doi.org/10.1063/1.3686909 (3 pages) | Cited 2 times

Online Publication Date: 22 February 2012

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We demonstrate a technique for determining the charge collection efficiency (ηCC) in bulk heterojunction organic photovoltaic cells (OPVs). To extract ηCC, we describe an approach to measure the optical absorption efficiency by examining the external quantum efficiency under reverse bias. Using estimates of the exciton diffusion efficiency obtained from photoluminescence quenching measurements, ηCC is calculated without any input from optical field simulations. For bulk heterojunction OPVs based on the donor-acceptor pairing of boron subphthalocyanine chloride and C60, a peak ηCC of (79 ± 2)% is realized for films containing 80 wt. % C60 under short-circuit conditions. This optimum composition also coincides with a peak in the fill factor and the short-circuit current density.
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88.40.hj Efficiency and performance of solar cells
88.40.jr Organic photovoltaics
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Small molecular phosphorescent organic light-emitting diodes using a spin-coated hole blocking layer

Yan Zhao, Lian Duan, Deqiang Zhang, Liudong Hou, Juan Qiao, Liduo Wang, and Yong Qiu

Appl. Phys. Lett. 100, 083304 (2012); http://dx.doi.org/10.1063/1.3688300 (4 pages) | Cited 3 times

Online Publication Date: 23 February 2012

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Small molecular green phosphorescent organic light-emitting diodes (OLEDs) have been studied using a solution processed polyethyleneoxide (PEO) hole blocking layer (HBL) and a Cs2CO3/Al cathode. PEO is soluable in alcoholic solvents and allows the fabrication of multilayer OLEDs by successive spin-coating. The current efficiency of the optimized OLED with the PEO HBL increases from 18.8 cd/A to 32.1 cd/A, and the turn-on voltage reduces from 4.8 V to 3.4 V, compared with the device without the PEO HBL. Photovoltaic measurements indicate that the injection barrier for electron is reduced by inserting the PEO layer. X-ray photoelectron spectroscopy measurements further reveal that improvement in device performance is due to the partial penetration of Cs into the PEO layer.
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85.60.Jb Light-emitting devices
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Solution doping of organic semiconductors using air-stable n-dopants

Yabing Qi, Swagat K. Mohapatra, Sang Bok Kim, Stephen Barlow, Seth R. Marder, and Antoine Kahn

Appl. Phys. Lett. 100, 083305 (2012); http://dx.doi.org/10.1063/1.3689760 (4 pages) | Cited 6 times

Online Publication Date: 24 February 2012

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Solution-based n-doping of the polymer poly{[N,N′-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)} [P(NDI2OD-T2)] and the small molecule 6,13-bis(tri(isopropyl)silylethynyl)pentacene (TIPS-pentacene) is realized with the air-stable dimers of rhodocene, [RhCp2]2, and ruthenium(pentamethylcyclopentdienyl)(1,3,5-triethylbenzene), [Cp*Ru(TEB)]2. Fermi level shifts, measured by direct and inverse photoemission spectroscopy, and orders of magnitude increase in current density and film conductivity point to strong n-doping in both materials. The strong reducing power of these air-stable dopants is demonstrated through the n-doping of TIPS-pentacene, a material with low electron affinity (3.0 eV). Doping-induced reduction of the hopping transport activation energy indicates that the increase in film conductivity is due in part to the filling of deep gap states by carriers released by the dopants.
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81.05.Fb Organic semiconductors
72.20.Ee Mobility edges; hopping transport
73.61.Ph Polymers; organic compounds
78.66.Qn Polymers; organic compounds
79.60.Bm Clean metal, semiconductor, and insulator surfaces
61.72.up Other materials
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