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Now showing items 1 - 4 of 4

  • 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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  • Simultaneous Enhancement of Brightness, Efficiency, and Switching in RGB Organic Light Emitting Transistors

    Ullah, Mujeeb   Tandy, Kristen   Yambem, Soniya D.   Aljada, Muhsen   Burn, Paul L.   Meredith, Paul   Namdas, Ebinazar B.  

    An innovative design strategy for light emitting field effect transistors (LEFETs) to harvest higher luminance and switching is presented. The strategy uses a nonplanar electrode geometry in tri-layer LEFETs for simultaneous enhancement of the key parameters of quantum efficiency, brightness, switching, and mobility across the RGB color gamut.
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  • Channel II photocurrent quantification in narrow optical gap polymer-fullerene solar cells with complimentary acceptor absorption

    Zhang, Yuliang   Pandey, Ajay K.   Tandy, Kristen   Dutta, Gitish K.   Burn, Paul L.   Meredith, Paul   Namdas, Ebinazar B.   Patil, Satish  

    Most charge generation studies on organic solar cells focus on the conventional mode of photocurrent generation derived from light absorption in the electron donor component (so called channel I). In contrast, relatively little attention has been paid to the alternate generation pathway: light absorption in the electron acceptor followed by photo-induced hole transfer (channel II). By using the narrow optical gap polymer poly(3,6-dithieno[3,2-b] thiophen-2-yl)-2,5-bis(2-octyldodecyl)-pyrrolo-[ 3,4-c]pyrrole-1,4-dione-5',5 ''-diyl-alt-4,8-bis(dodecyloxy) benzo[1,2-b:4,5-b'] dithiophene-2,6-diyl with two complimentary fullerene absorbers; phenyl-C-61-butyric acid methyl ester, and phenyl-C-71-butyric acid methyl ester (70-PCBM), we have been able to quantify the photocurrent generated each of the mechanisms and find a significant fraction (>30%), which is derived in particular from 70-PCBM light absorption. (C) 2013 AIP Publishing LLC.
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  • Host-Free Blue Phosphorescent Dendrimer Organic Light-Emitting Field-Effect Transistors and Equivalent Light-Emitting Diodes:A Comparative Study

    Ullah, Mujeeb   Tandy, Kristen   Clulow, Andrew J.   Burn, Paul L.   Gentle, Ian R.   Meredith, Paul   Lo, Shih-Chun   Namdas, Ebinazar B.  

    Light-emitting field-effect transistors (LEFETs) integrate functions of an organic light-emitting diode (OLED) and a field-effect transistor, and hence offer significant advantages in simplifying the device architecture for next-generation active matrix full-color displays as well as having potential in communications and electrically pumped lasers. There is little work on phosphorescent light-emitting field-effect transistors, particularly those based on host-free phosphorescent light-emitting materials. In this report, we demonstrate solution-processed host-free LEFETs and OLEDs based on a blue phosphorescent dendrimer as the active emitter and compare their performance. The LEFETs exhibit excellent electrical and optical characteristics with a luminance of 650 cd m(-2) and an EQE of 2.1%, which is comparable to the equivalent OLEDs based on the same dendrimer. The LEFETs were fabricated in a heterostructure bilayer configuration using a p-type charge transport material, poly(2,5-bis(3-n-hexadecylthiophene-2-yOthieno[3,2-b]thiophene) (PBTTT), underneath the emissive layer. The equivalent OLEDs were fabricated using PBTTT and MoOx, as the hole-injecting and -transporting layers. Remarkably, negligible EQE roll -off in the LEFETs at high current density and brightness was observed. These results indicate that for phosphorescent materials there could be an advantage in using LEFETs over OLEDs at high current density or brightness. In addition, we discuss the operating mechanism and effects of solvent used to deposit the dendrimer layer on the interface formed with the PBTTT layer. X-ray reflectometry showed that the interface between the PBTTT and dendrimer layer changed in terms of the lamellar ordering of the PBTTT layer upon solution deposition of the dendrimer layer, resulting in a lower charge carrier mobility in the devices.
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