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Now showing items 1 - 16 of 37

  • A thiocarbonyl-containing small molecule for optoelectronics

    Gendron, David   Maasoumi, Fatemeh   Armin, Ardalan   Pattison, Katherine   Burn, Paul L.   Meredith, Paul   Namdas, Ebinazar B.   Powell, Benjamin J.  

    We report the synthesis and characterization of a novel thiocarbonyl iso-DPP derivative, namely 1,3,4,6-tetraphenylpyrrolo[3,2-b]pyrrole-2,5(1H, 4H)-dithione. Even without solubilising alkyl chains, the small molecule could be processed from organic solvents such as dichloromethane, chloroform or dichlorobenzene, and it was found that the optical properties of neat thin films were strongly dependent on the solvent used. Field effect hole mobilities were of the order 10(-4) cm(2) V-1 s(-1), with mobilities measured in a diode configuration solvent dependent and at least an order of magnitude lower. Importantly, blends of the iso-DPP derivative with PC70BM, a typically used electron acceptor in bulk heterojunction solar cells, were found to possess hole mobilities of up to 10(-3) cm(2) V-1 s(-1) in a diode configuration, which was an order of magnitude larger than the electron mobility. Finally, simple bulk heterojunction solar cells were fabricated with maximum power conversion efficiencies of 2.3%.
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  • High-Performance, Solution-Processed Non-polymeric Organic Photodiodes

    Kim, Il Ku   Pal, Bhola N.   Ullah, Mujeeb   Burn, Paul L.   Lo, Shih-Chun   Meredith, Paul   Namdas, Ebinazar B.  

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  • Mobility Evaluation of BTBT Derivatives: Limitation and Impact on Charge Transport

    Wawrzinek, Robert   Sobus, Jan   Chaudhry, Mujeeb Ullah   Ahmad, Viqar   Grosjean, Arnaud   Clegg, Jack K.   Namdas, Ebinazar B.   Lo, Shih-Chun  

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  • Hybrid Area-Emitting Transistors:Solution Processable and with High Aperture Ratios

    Muhieddine, Khalid   Ullah, Mujeeb   Maasoumi, Fatemeh   Burn, Paul L.   Namdas, Ebinazar B.  

    Area emission is realized in all-solution-processed hybrid light-emitting transistors (HLETs). A new HLET design is presented with increased aperture ratio, and optical and electrical characteristics are shown.
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  • Organic light emitting complementary inverters

    Namdas, Ebinazar B.   Samuel, Ifor D. W.   Shukla, Deepak   Meyer, Dianne M.   Sun, Yanming   Hsu, Ben B. Y.   Moses, Daniel   Heeger, Alan J.  

    We show that p- and n-type light emitting field-effect transistors (LEFETs) can be made using "superyellow" as a light-emitting polymer, poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene) as a p-type material and a naphthalene di-imide as an n-type material. By connecting two of these LEFETs, we have demonstrated a light emitting complementary inverter (LECI). The LECI exhibited electrical and optical characteristics in the first and third quadrant of the transfer characteristics with voltage gain of 6 and 8, respectively.
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  • Organic light emitting complementary inverters RID F-5849-2010

    Namdas, Ebinazar B.   Samuel, Ifor D. W.   Shukla, Deepak   Meyer, Dianne M.   Sun, Yanming   Hsu, Ben B. Y.   Moses, Daniel   Heeger, Alan J.  

    We show that p- and n-type light emitting field-effect transistors (LEFETs) can be made using "superyellow" as a light-emitting polymer, poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene) as a p-type material and a naphthalene di-imide as an n-type material. By connecting two of these LEFETs, we have demonstrated a light emitting complementary inverter (LECI). The LECI exhibited electrical and optical characteristics in the first and third quadrant of the transfer characteristics with voltage gain of 6 and 8, respectively.
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  • High-Performance,Fullerene-Free Organic Photodiodes Based on a Solution-Processable Indigo

    Kim, Il Ku   Li, Xin   Ullah, Mujeeb   Shaw, Paul E.   Wawrzinek, Robert   Namdas, Ebinazar B.   Lo, Shih-Chun  

    A solution-processable dibromoindigo with an alkyoxyphenyl solubilizing group is developed and used as a new electron acceptor in organic photodiodes. The solution-processed fullerene-free organic photodiodes show an almost spectrally flat response with a high responsivity (0.4 A W-1) and a high detectivity (1 x 10(12) Jones). These values are comparable to silicon-based photodiodes.
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  • Phosphorescent Light-Emitting Transistors: Harvesting Triplet Excitons

    Namdas, Ebinazar B.   Hsu, Ben B. Y.   Liu, Zehua   Lo, Shih-Chun   Burn, Paul L.   Samuel, Ifor D. W.  

    Phosphorescent light-emitting transistors, in which light emission from singlet and triplet energy levels is harvested using solution-processed materials (see figure), are presented. While a green phosphorescent dendrimer exhibits an external quantum efficiency of 0.45% at 480 cd m(-2), a red polymer/phosphorescent small-molecule blend produces a brightness exceeding 30 cd m(-2) with a relatively high hole mobility of 2.5 x 10(-2) cm(2) V(-1) s(-1).
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  • Conjugated polyelectrolytes for organic light emitting transistors RID F-5849-2010

    Seo, Jung Hwa   Namdas, Ebinazar B.   Gutacker, Andrea   Heeger, Alan J.   Bazan, Guillermo C.  

    We report on solution-processed light emitting field-effect transistors (LEFETs) that incorporate symmetric high work function (WF) source and drain metal electrodes. A key architectural design is the incorporation of a conjugated polyelectrolyte (CPE) electron injection layer atop the emissive layer. The device structure also comprises a hole-transporting layer underneath the emissive layer. Both holes and electrons are injected from stable, high WF metal though the CPE layer leading to electroluminescence near the electron-injecting electrode. With the benefits of the simplicity in device fabrication, the LEFETs incorporating CPEs are interesting structures for integrated organic optoelectronic devices. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3467856]
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  • Gate-controlled light emitting diodes RID F-5849-2010

    Namdas, Ebinazar B.   Swensen, James S.   Ledochowitsch, Peter   Yuen, Jonathan D.   Moses, Daniel   Heeger, Alan J.  

    The structure and operation of a gate-controlled LED is reported (see figure). The device is properly described as a unipolar organic transistor in series with an OLED. Light emission was visible with brightness exceeding 310cd m(-2) at external quantum efficiency of 0.5%; the brightness is controlled by the gate voltage.
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  • High performance light emitting transistors

    Namdas, Ebinazar B.   Ledochowitsch, Peter   Yuen, Jonathan D.   Moses, Daniel   Heeger, Alan J.  

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  • High performance light emitting transistors RID F-5849-2010

    Namdas, Ebinazar B.   Ledochowitsch, Peter   Yuen, Jonathan D.   Moses, Daniel   Heeger, Alan J.  

    Solution processed light emitting field-effect transistors (LEFETs) with peak brightness exceeding 2500 cd/m(2) and external quantum efficiency of 0.15% are demonstrated. The devices utilized a bilayer film comprising a hole transporting polymer, poly (2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b] thiophene) and a light emitting polymer, Super Yellow, a polyphenylenevinylene derivative. The LEFETs were fabricated in the bottom gate architecture with top-contact Ca/Ag as source/drain electrodes. Light emission was controlled by the gate voltage which controls the hole current. These results indicate that high brightness LEFETs can be made by using the bilayer film (hole transporting layer and a light emitting polymer). (C) 2008 American Institute of Physics.
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  • Nonlinear transport in semiconducting polymers at high carrier densities RID B-9530-2008

    Yuen, Jonathan D.   Menon, Reghu   Coates, Nelson E.   Namdas, Ebinazar B.   Cho, Shinuk   Hannahs, Scott T.   Moses, Daniel   Heeger, Alan J.  

    Conducting and semiconducting polymers are important materials in the development of printed, flexible, large-area electronics such as flat-panel displays and photovoltaic cells. There has been rapid progress in developing conjugated polymers with high transport mobility required for high-performance field-effect transistors (FETs), beginning(1) with mobilities around 10(-4) cm(2) V(-1) s(-1) to a recent report(2) of 1 cm(2) V(-1) s(-1) for poly(2,5-bis(3-tetradecylthiophen-2-yl) thieno[3,2-b] thiophene) (PBTTT). Here, the electrical properties of PBTTT are studied at high charge densities both as the semiconductor layer in FETs and in electrochemically doped films to determine the transport mechanism. We show that data obtained using a wide range of parameters (temperature, gate-induced carrier density, source-drain voltage and doping level) scale onto the universal curve predicted for transport in the Luttinger liquid description of the one-dimensional 'metal'.
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  • Simple color tuning of phosphorescent dendrimer light emitting diodes

    Namdas, Ebinazar B.   Anthopoulos, Thomas D.   Samuel, Ifor D. W.   Frampton, Michael J.   Lo, Shih-Chun   Burn, Paul L.  

    A simple way of tuning the emission color in solution processed phosphorescent organic light emitting diodes is demonstrated. For each color a single emissive spin-coated layer consisting of a blend of three materials, a fac-tris(2-phenylpyridyl)iridium (III) cored dendrimer (Ir-G1) as the green emitter, a heteroleptic [bis(2-phenylpyridyl)-2-(2'-benzo[4,5-alpha]thienyl)pyridyl] iridium (III) cored dendrimer [Ir(ppy)(2)btp] as the red emitter, and 4,4'-bis(N-carbazolyl) biphenyl (CBP) as the host was employed. By adjusting the relative amount of green and red dendrimers in the blends, the color of the light emission was tuned from green to red. High efficiency two layer devices were achieved by evaporating a layer of electron transporting 1,3,5-tris(2-N-phenylbenzimidazolyl)benzene (TPBI) on top of the spin-coated emissive layer. A brightness of 100 cd/m(2) was achieved at drive voltages in the range 5.3-7.3 V. The peak external efficiencies at this brightness ranged from 31 cd/A (18 lm/W) to 7 cd/A (4 lm/W). (c) 2005 American Institute of Physics.
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  • Control of Efficiency, Brightness, and Recombination Zone in Light-Emitting Field Effect Transistors

    Hsu, Ben B. Y.   Duan, Chunhui   Namdas, Ebinazar B.   Gutacker, Andrea   Yuen, Jonathan D.   Huang, Fei   Cao, Yong   Bazan, Guillermo C.   Samuel, Ifor D. W.   Heeger, Alan J.  

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  • A new diketopyrrolopyrrole-based co-polymer for ambipolar field-effect transistors and solar cells

    Tandy, Kristen   Dutta, Gitish K.   Zhang, Yuliang   Venkatramaiah, N.   Aljada, Muhsen   Burn, Paul L.   Meredith, Paul   Namdas, Ebinazar B.   Patil, Satish  

    A new thieno[3,2-b]thiophenediketopyrrolopyrrole-benzo[1,2-b:4,5-b']dithiophene based narrow optical gap co-polymer (PTTDPP-BDT) has been synthesized and characterized for field-effect transistors and solar cells. In field-effect transistors the polymer exhibited ambipolar charge transport behaviour with maximum hole and electron mobilities of 10(-3) cm(2) V-1 s(-1) and 10(-5) cm(2)V(-1) s(-1), respectively. The respectable charge transporting properties of the polymer were consistent with X-ray diffraction measurements that showed close molecular packing in the solid state. The difference in hole and electron mobilities was explained by density functional theory calculations, which showed that the highest occupied molecular orbital was delocalized along the polymer backbone with the lowest unoccupied molecular orbital localized on the bis(thieno[3,2-b]thiophene)diketopyrrolopyrrole units. Bulk heterojunction photovoltaic devices with the fullerene acceptor PC70BM were fabricated and delivered a maximum conversion efficiency of 3.3% under AM1.5G illumination. (C) 2012 Elsevier B.V. All rights reserved.
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