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Now showing items 1 - 16 of 42

  • Tuning the Optoelectronic Properties of Nonfullerene Electron Acceptors

    Fang, Yuan   Pandey, Ajay K.   Lyons, Dani M.   Shaw, Paul E.   Watkins, Scott E.   Burn, Paul L.   Lo, Shih-Chun   Meredith, Paul  

    Broad spectral coverage over the solar spectrum is necessary for photovoltaic technologies and is a focus for organic solar cells. We report a series of small-molecule, nonfullerene electron acceptors containing the [(benzo[c][1,2,5]thiadiazol-4-yl)methylene]malononitrile unit as a high electron affinity component. The optoelectronic properties of these molecules were fine-tuned with the objective of attaining strong absorption at longer wavelengths by changing the low-ionization-potential moiety. The electron-accepting function of these materials was investigated with poly(3-n-hexylthiophene) (P3HT) as a standard electron donor. Significant photocurrent generation in the near infrared region, with an external quantum yield reaching as high as 22% at 700 nm and an onset >800 nm was achieved. The results support efficient hole transfer to P3HT taking place after light absorption by the acceptor molecules. A Channel II-dominated power conversion efficiency of up to 1.5% was, thus, achieved.
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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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    In a general form, there is provided a cyclometalated iridium complex, which in one application can be used as a catalyst for water splitting. In one form, the cyclometalated iridium complex includes bandgap lowering ligands, for example aryl quinoline. In another form, the cyclometalated iridium complex includes bandgap widening ligands, for example aryl triazole. In a particular example, one or more additional linking groups are included to improve solubility of the complex. In another particular example, one or more additional linking groups are included to improve attachment of the complex to a semiconductor or an electrode. According to a specific example, there is a cyclometalated iridium complex having the structure wherein, Ar is an aryl group, or a fused or heterocyclic arene or ring.
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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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  • The 'double dendron' approach to host free phosphorescent poly(dendrimer) OLEDs

    Lai, Wen-Yong   Levell, Jack W.   Balfour, Michael N.   Burn, Paul L.   Lo, Shih-Chun   Samuel, Ifor D. W.  

    The addition of dendrons to iridium(III) complexes attached to a poly(styrene) backbone is shown to improve the physical and optoelectronic properties of the phosphorescent materials. The iridium(III) complexes have two 2-phenylpyridyl ligands and one phenyltriazolyl ligand, with the latter providing the attachment point to the polymer backbone. It was found that by increasing the number of dendrons (from zero to two) per 2-phenylpyridyl ligand, the intra-and interchain interactions could be more effectively controlled. The poly(dendrimer) with two dendrons per ligand had solution and solid-state photoluminescence quantum yields of 67% and 47%, respectively. Organic light-emitting diodes containing the doubly dendronised (two dendrons per ligand) poly(dendrimer) had a low turn on voltage of 3.6 V (>1.0 cd m(-2)), a maximum luminance of 6 700 cd m(-2) (at 12.2 V), and 100 cd m(-2) was achieved at 6.0 V with an external quantum efficiency (EQE) of 9.2% (28.1 cd A-1) and power efficiency of 14.7 lm/W. A solution of the doubly dendronised poly(dendrimer) in N-methyl-2-pyrolidinone was found to have a viscosity of 4.6 mPa s, which falls in the range of solutions that can be inkjet printed.
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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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  • The development of phenylethylene dendrons for blue phosphorescent emitters

    Lo, Shih-Chun   Harding, Ruth E.   Brightman, Edward   Burn, Paul L.   Samuel, Ifor D. W.  

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  • Electrochemically tuneable multi-colour electrochemiluminescence using a single emitter

    Haghighatbin, Mohammad A.   Lo, Shih-Chun   Burn, Paul L.   Hogan, Conor F.  

    A single starting component electrochemiluminescence system from which red, green, blue or white emission can be obtained, depending on the applied potential or the mode of the ECL experiment, is described. The convoluted ECL spectral responses observed at different potentials are readily explained using a 3D-ECL technique, where the ECL spectral profile is continuously monitored as a function of potential during voltammetric scanning. The 3D plots obtained using this technique implicate cross-annihilation ECL reactions involving the complex itself and stable products resulting from its electrolysis. Combining this information with knowledge of the energetic requirements of the various reactions involved, suggests a mechanism involving traces of two emissive products, related to the loss of a methyl group from the triazole moiety. These products, while barely detectable electrochemically, are sufficiently emissive to influence and even dominate the ECL emission under some conditions.
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  • The development of light-emitting dendrimers for displays RID B-4369-2010

    Burn, Paul L.   Lo, Shih-Chun   Samuel, Ifor D. W.  

    Dendrimers are now an important class of light-emitting material for use in organic light-emitting diodes (OLEDs). Dendrimers are branched macromolecules that consist of a core, one or more dendrons, and surface groups. The different parts of the macromolecule can be selected to give the desired optoelectronic and processing properties. The first light-emitting dendrimers were fluorescent but more recently highly efficient phosphorescent dendrimers have been developed. OLEDs containing light-emitting dendrimers have been reported to have external quantum efficiencies of up to 16%. The solubility of the dendrimers opens the way for simple processing and a new class of flat-panel displays. In this Review we show how the structure of the light-emitting dendrimers controls key features such as intermolecular interactions and charge transport, which are important for all OLED materials. The advantages of the dendrimer architecture for phosphorescent emitters and the way the structure can be varied to enhance materials performance and device design are illustrated.
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  • Blue Phosphorescence from Iridium(III) Complexes at Room Temperature

    Lo, Shih-Chun   Shipley, Christopher P.   Bera, Raghu N.   Harding, Ruth E.   Cowley, Andrew R.   Burn, Paul L.   Samuel, Ifor D. W.  

    We report a new family of homoleptic iridium(III) complexes that emit blue phosphorescence at room temperature. The iridium( III) complexes are comprised of phenyltriazole ligands and were easily prepared via short synthetic routes. The parent fac-tris(1-methyl-5-phenyl-3-propyl-[1,2,4]triazolyl)iridium(III) complex exhibits blue photoluminescence (PL) with emission peaks at 449 and 479 nm and has a solution PL quantum yield of 66%. The emission was sequentially blue-shifted by the attachment of one and two fluorine atoms to the ligand phenyl ring with the fac-tris{1-methyl-5-(4,6-difluorophenyl)-3-propyl-[1,2,4]triazolyl} iridium( III) complex having the 1931 Commission Internationale de l'Eclairage coordinates of (0.16, 0.12) at room temperature. In contrast, when the phenyl ring of the ligands was substituted by trifluoromethyl, the PL spectrum was red-shifted when compared to the parent compound whereas if the trifluoromethyl group was attached to the triazole ring, the emission was blue-shifted. The radiative rates of these new blue iridium( III) complexes were found to be in the range of 2-6 x 105 s(-1), indicating that the emission had varying amounts of metal-to-ligand charge-transfer character. Molecular orbital calculations showed that for the fluorinated complexes the contribution of the ligand triplet character to the emissive energy state increased with the hypsochromic shift in emission. This was confirmed by time-resolved PL measurements, which showed that the complex with the deepest blue emission had the slowest radiative decay rate.
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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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  • A dendronised polymer for bulk heterojunction solar cells RID A-1507-2011 RID B-4369-2010

    Yu, Justin   Lee, Kwan H.   Zhang, Yuliang   Klein, Michael F. G.   Colsmann, Alexander   Lemmer, Uli   Burn, Paul L.   Lo, Shih-Chun   Meredith, Paul  

    A Gilch polymerisation was used to form a high molecular weight poly[1,4-phenylenevinylene] with pendent first generation biphenyl dendrons attached to every monomer unit of the backbone. The attachment of the bulky side-chain was found not to disrupt the conjugation of the polymer backbone and the polymer formed an ordered intramolecular structure in the solid-state. Bulk heterojunction (BHJ) organic solar cells were manufactured by blending the polymer at different ratios with [6,6]-phenyl-C(61)-butyric acid methyl ester (PCBM). Under AM1.5 testing conditions the device with the polymer: PCBM ratio 1 : 3 by weight was found to have an optimum V(oc) = 0.86 V, J(sc) = 1.4 mA cm(-2), FF = 37% and PCE of 0.44%, with the PCE 30 times higher than the only other report on a dendronised polymer used in a BHJ device.
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  • Development of Dendrimers:? Macromolecules for Use in Organic Light-Emitting Diodes and Solar Cells

    Lo, Shih-Chun   Burn, Paul L.  

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  • Energetic requirements of iridium(III) complex based photosensitisers in photocatalytic hydrogen generation

    Fan, Shengqiang   Zong, Xu   Shaw, Paul E.   Wang, Xin   Geng, Yan   Smith, Arthur R. G.   Burn, Paul L.   Wang, Lianzhou   Lo, Shih-Chun  

    A new family of Ir(III) complexes were synthesised and employed as light-induced hydrogen-production photosensitisers in aqueous systems, where hydrogen evolution was observed only when the PS* was reduced by the sacrificial agent, NEt3, signifying that a minimum potential difference of >0.2 V between E(PS*/PS-) and E(NEt3+/NEt3) is required for efficient hydrogen production [i.e., E(PS*/PS-) >1.19 V versus NHE].The analytical method developed here is demonstrated to be useful for screening new photosensitisers for light-driven hydrogen generation.
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  • Efficient Phosphorescence by Reducing lntrachain Chromophore Interactions in Dendrimer-Containing Polymers

    Levell, Jack W.   Lai, Wen-Yong   Borthwick, Robert J.   Lo, Shih-Chun   Burn, Paul L.   Samuel, Ifor D. W.  

    Poly(dendrimers) comprised of a poly(styrene) backbone with dendrimer side chains containing an iridium(III) complex core, first-generation biphenyl dendrons, and (2-ethylhexyl)oxy surface groups show increased viscosity compared to their individual dendrimer components, which is important for inkjet printing processes. However, intrachain interchromophore interactions lead to lower photoluminescence quantum yields even in solution relative to the simple isolated dendrimers. We demonstrate that the phosphorescence efficiency of a polymer can be enhanced by incorporating the dendrirner monomer unit(s) into a copolymer with poly(styrene) spacer units. The poly(styrene) spacer units remove the intrachain interchromophore interactions between the chromophores in solution. The copolymer gives a >50% increase in solution photoluminescence quantum yields (to 94%) and an improved organic light-emitting diode performance with an external quantum efficiency of 6.7% at 100 cd/m(2) at 11 V when compared to the homopolymer with the same dendrimer side chain.
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  • High-Speed OLEDs and Area-Emitting Light-Emitting Transistors from a Tetracyclic Lactim Semiconducting Polymer

    Ahmad, Viqar   Shukla, Atul   Sobus, Jan   Sharma, Anirudh   Gedefaw, Desta   Andersson, Gunther G.   Andersson, Mats R.   Lo, Shih-Chun   Namdas, Ebinazar B.  

    Development of a new class of luminescent materials that show high-speed response, high charge carrier mobility, and high brightness is desirable toward realization of next generation of devices, such as electrically pumped organic lasers, visible light communication instruments, and organic light-emitting transistors. In this paper, high-speed organic light-emitting diodes (OLEDs) and high-performance hybrid light-emitting transistors from a new type of solution processable luminescent material, poly[thiophene-2,5-diyl-alt-5,10-bis((2-hexyldecyl)oxy)dithieno[3,2-c:3 ',2 '-h][1,5]naphthyridine-2,7-diyl] (PTNT), are reported. The OLEDs based on PTNT polymer exhibit a peak brightness of 8 x 10(5) cd m(-2) and 40 MHz modulation frequency under 10 ns pulse operation. This modulation frequency is significantly higher than that of commercially available LEDs, used for visible light communication. Additionally, solution-processed area-emitting hybrid light-emitting transistors with an external quantum yield of 0.25% at brightness of 250 cd m(-2) are demonstrated. Finally, the paper provides device physics and optoelectronic properties of PTNT polymer using ultraviolet photon spectroscopy, inversed photoelectron spectroscopy, and photophysical measurements.
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