Publications
203 results found
Wood S, Kim J-H, Wade J, et al., 2016, Systematic control of heteroatoms in donor-acceptor copolymers and its effects on molecular conformation and photovoltaic performance, JOURNAL OF MATERIALS CHEMISTRY C, Vol: 4, Pages: 7966-7978, ISSN: 2050-7526
Perevedentsev A, Chander N, Kim J-S, et al., 2016, Spectroscopic properties of poly(9,9-dioctylfluorene) thin films possessing varied fractions of -phase chain segments: enhanced photoluminescence efficiency via conformation structuring, Journal of Polymer Science Part B-Polymer Physics, Vol: 54, Pages: 1995-2006, ISSN: 1099-0488
Poly(9,9-dioctylfluorene) (PFO) is a widely studied blue-emitting conjugated polymer, the optoelectronic properties of which are strongly affected by the presence of a well-defined chain-extended “β-phase” conformational isomer. In this study, optical and Raman spectroscopy are used to systematically investigate the properties of PFO thin films featuring a varied fraction of β-phase chain segments. Results show that the photoluminescence quantum efficiency (PLQE) of PFO films is highly sensitive to both the β-phase fraction and the method by which it was induced. Notably, a PLQE of ∼69% is measured for PFO films possessing a ∼6% β-phase fraction induced by immersion in solvent/nonsolvent mixtures; this value is substantially higher than the average PLQE of ∼55% recorded for other β-phase films. Furthermore, a linear relationship is observed between the intensity ratios of selected Raman peaks and the β-phase fraction determined by commonly used absorption calibrations, suggesting that Raman spectroscopy can be used as an alternative means to quantify the β-phase fraction. As a specific example, spatial Raman mapping is used to image a mm-scale β-phase stripe patterned in a glassy PFO film, with the extracted β-phase fraction showing excellent agreement with the results of optical spectroscopy.
Razzell-Hollis J, Limbu S, Kim J-S, 2016, Spectroscopic investigations of three-phase morphology evolution in polymer: fullerene solar cell blends, Journal of Physical Chemistry C, Vol: 120, Pages: 10806-10814, ISSN: 1932-7447
Nanoscale morphology is critical to determining the device efficiency of bulk heterojunction organic solar cells, and the ideal structure is often described as a three-phase network with one well-mixed phase for efficient charge separation and two purer phases for efficient charge transport. In order to understand such nanoscale morphology, we have performed detailed spectroscopic investigations and identified the three-phase morphology evolution in one of the classic blend systems, P3HT:PCBM. The impact of different phases on polymer molecular (chain conformational) order and blend thermal and optical properties were monitored in situ using resonant Raman, absorption, and photoluminescence spectroscopy techniques. Semicrystalline P3HT was found to accommodate up to ∼25% PCBM (by weight) in its amorphous phase, with very little impact on either polymer molecular order or aggregation. Higher concentrations of PCBM resulted in a greater proportion of amorphous mixed phase and reduced polymer molecular order and aggregation. On the other hand, the formation of crystalline purer phases via phase separation was evident during in situ thermal annealing, revealing a consistent glass transition temperature (Tg) of ∼50 °C in blends with up to 50% wt PCBM. This indicates similar local chemical compositions in the amorphous mixed phase present in blends despite different overall blend ratios. A much higher Tg (80–100 °C) was observed for blends with >50% wt PCBM, indicating a stronger impact of PCBM on P3HT molecular order and thermal properties, requiring a higher annealing temperature to ensure formation of the preferred three-phase morphology.
Bogatko SA, Haynes PD, Sathian J, et al., 2016, Molecular design of a room-temperature maser, The Journal of Physical Chemistry C, Vol: 120, Pages: 8251-8260, ISSN: 1932-7447
Kim J-H, Wood S, Park JB, et al., 2016, Optimization and Analysis of Conjugated Polymer Side Chains for High-Performance Organic Photovoltaic Cells, ADVANCED FUNCTIONAL MATERIALS, Vol: 26, Pages: 1517-1525, ISSN: 1616-301X
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- Citations: 61
Kang C-M, Wade J, Yun S, et al., 2016, 1 GHz Pentacene Diode Rectifiers Enabled by Controlled Film Deposition on SAM-Treated Au Anodes, ADVANCED ELECTRONIC MATERIALS, Vol: 2, ISSN: 2199-160X
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- Citations: 46
Suh M, Bailey J, Kim SW, et al., 2015, High-Efficiency Polymer LEDs with Fast Response Times Fabricated via Selection of Electron-Injecting Conjugated Polyelectrolyte Backbone Structure., ACS Applied Materials & Interfaces, Vol: 7, Pages: 26566-26571, ISSN: 1944-8244
Imidazolium ionic side-group-containing fluorene-based conjugated polyelectrolytes (CPEs) with different π-conjugated structures, poly[(9,9-bis(8'-(3″-methyl-1″-imidazolium)octyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] dibromide (F8im-Br) and poly[(9,9-bis(8'-(3″-methyl-1″-imidazolium)octyl)-2,7-fluorene)-alt-(benzo(2,1,3)thiadiazol-4,8-diyl) dibromide (F8imBT-Br), are synthesized and utilized as an electron injection layer (EIL) in green-emitting F8BT polymer light-emitting diodes (PLEDs). Both CPE EIL devices significantly outperform Ca cathode devices; 17.9 cd A(-1) (at 3.8 V) and 16.6 lm W(-1) (at 3.0 V) for F8imBT-Br devices, 11.1 cd A(-1) (at 4.2 V) and 9.1 lm W(-1) (at 3.4 V) for F8im-Br devices, and 7.2 cd A(-1) (at 3.6 V) and 7.0 lm W(-1) (at 3.0 V) for Ca devices. Importantly, unlike the F8im-Br EIL devices, F8imBT-Br PLEDs exhibit much faster electroluminescence turn-on times (<10 μs) despite both EILs possessing the same tethered imidazolium and mobile bromide ions. The F8imBT-Br devices represent, to the best of our knowledge, the highest efficiency in thin (70 nm) single-layer F8BT PLEDs in conventional device architecture with the fastest EL response time using CPE EIL with mobile ions. Our results clearly indicate the importance of an additional factor of EIL materials, specifically the conjugated backbone structure, to determine the device efficiency and response times.
Abdulla M, Renero-Lecuna C, Kim JS, et al., 2015, Morphological study of F8BT:PFB thin film blends, ORGANIC ELECTRONICS, Vol: 23, Pages: 87-98, ISSN: 1566-1199
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- Citations: 8
Wade J, Wood S, Beatrup D, et al., 2015, Operational electrochemical stability of thiophene-thiazole copolymers probed by resonant Raman spectroscopy., Journal of Chemical Physics, Vol: 142, Pages: 244904-244904, ISSN: 1089-7690
We report on the electrochemical stability of hole polarons in three conjugated polymers probed by resonant Raman spectroscopy. The materials considered are all isostructural to poly(3-hexyl)thiophene, where thiazole units have been included to systematically deepen the energy level of the highest occupied molecular orbital (HOMO). We demonstrate that increasing the thiazole content planarizes the main conjugated backbone of the polymer and improves the electrochemical stability in the ground state. However, these more planar thiazole containing polymers are increasingly susceptible to electrochemical degradation in the polaronic excited state. We identify the degradation mechanism, which targets the C=N bond in the thiazole units and results in disruption of the main polymer backbone conjugation. The introduction of thiazole units to deepen the HOMO energy level and increase the conjugated backbone planarity can be beneficial for the performance of certain optoelectronic devices, but the reduced electrochemical stability of the hole polaron may compromise their operational stability.
Wood S, Kim J-H, Hwang D-H, et al., 2015, Effects of Fluorination and Side Chain Branching on Molecular Conformation and Photovoltaic Performance of Donor-Acceptor Copolymers, CHEMISTRY OF MATERIALS, Vol: 27, Pages: 4196-4204, ISSN: 0897-4756
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- Citations: 39
Fei Z, Boufflet P, Wood S, et al., 2015, Influence of backbone fluorination in regioregular poly(3-alkyl-4-fluoro)thiophenes, Journal of the American Chemical Society, Vol: 137, Pages: 6866-6879, ISSN: 1520-5126
We report two strategies toward the synthesis of 3-alkyl-4-fluorothiophenes containing straight (hexyl and octyl) and branched (2-ethylhexyl) alkyl groups. We demonstrate that treatment of the dibrominated monomer with 1 equiv of alkyl Grignard reagent leads to the formation of a single regioisomer as a result of the pronounced directing effect of the fluorine group. Polymerization of the resulting species affords highly regioregular poly(3-alkyl-4-fluoro)thiophenes. Comparison of their properties to those of the analogous non-fluorinated polymers shows that backbone fluorination leads to an increase in the polymer ionization potential without a significant change in optical band gap. Fluorination also results in an enhanced tendency to aggregate in solution, which is ascribed to a more co-planar backbone on the basis of Raman and DFT calculations. Average charge carrier mobilities in field-effect transistors are found to increase by up to a factor of 5 for the fluorinated polymers.
Higgins SG, Muir BVO, Wade J, et al., 2015, Organic Transistors: Self-Aligned Megahertz Organic Transistors Solution-Processed on Plastic (Adv. Electron. Mater. 5/2015), Advanced Electronic Materials, Vol: 1
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- Citations: 1
Higgins SG, Muir BVO, Wade J, et al., 2015, Self-aligned megahertz organic transistors solution-processed on plastic, Advanced Electronic Materials, Vol: 1, ISSN: 2199-160X
Hellmann C, Treat ND, Scaccabarozzi AD, et al., 2015, Solution Processing of Polymer Semiconductor: Insulator Blends-Tailored Optical Properties Through Liquid-Liquid Phase Separation Control, JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS, Vol: 53, Pages: 304-310, ISSN: 0887-6266
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- Citations: 27
Perevedentsev A, Sonnefraud Y, Belton CR, et al., 2015, Dip-pen patterning of poly(9,9-dioctylfluorene) chain-conformation-based nano-photonic elements, Nature Communications, Vol: 6, Pages: 1-9, ISSN: 2041-1723
Metamaterials are a promising new class of materials, in which sub-wavelength physical structures, rather than variations in chemical composition, can be used to modify the nature of their interaction with electromagnetic radiation. Here we show that a metamaterials approach, using a discrete physical geometry (conformation) of the segments of a polymer chain as the vector for a substantial refractive index change, can be used to enable visible wavelength, conjugated polymer photonic elements. In particular, we demonstrate that a novel form of dip-pen nanolithography provides an effective means to pattern the so-called β-phase conformation in poly(9,9-dioctylfluorene) thin films. This can be done on length scales ≤500 nm, as required to fabricate a variety of such elements, two of which are theoretically modelled using complex photonic dispersion calculations.
Kim JS, Wood S, Shoaee S, et al., 2015, Morphology-performance relationships in polymer/fullerene blends probed by complementary characterisation techniques - effects of nanowire formation and subsequent thermal annealing, JOURNAL OF MATERIALS CHEMISTRY C, Vol: 3, Pages: 9224-9232, ISSN: 2050-7526
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- Citations: 10
Wood S, Wade J, Shahid M, et al., 2015, Natures of optical absorption transitions and excitation energy dependent photostability of diketopyrrolopyrrole (DPP)-based photovoltaic copolymers, ENERGY & ENVIRONMENTAL SCIENCE, Vol: 8, Pages: 3222-3232, ISSN: 1754-5692
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- Citations: 73
Wade J, Steiner F, Niedzialek D, et al., 2014, Charge mobility anisotropy of functionalized pentacenes in organic field effect transistors fabricated by solution processing, JOURNAL OF MATERIALS CHEMISTRY C, Vol: 2, Pages: 10110-10115, ISSN: 2050-7526
Lee S, Lee BR, Kim J-S, et al., 2014, Combination effect of polar solvent treatment on ZnO and polyfluorene-based polymer blends for highly efficient blue-based hybrid organic-inorganic polymer light-emitting diodes, JOURNAL OF MATERIALS CHEMISTRY C, Vol: 2, Pages: 8673-8677, ISSN: 2050-7526
Lee BR, Jung ED, Park JS, et al., 2014, Highly efficient inverted polymer light-emitting diodes using surface modifications of ZnO layer, NATURE COMMUNICATIONS, Vol: 5, ISSN: 2041-1723
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- Citations: 119
Kim JS, Fei Z, Wood S, et al., 2014, Germanium- and Silicon-Substituted Donor–Acceptor Type Copolymers: Effect of the Bridging Heteroatom on Molecular Packing and Photovoltaic Device Performance, Advanced Energy Materials
The effects of heteroatom substitution from a silicon atom to a germanium atom in donor-acceptor type low band gap copolymers, poly[(4,4′-bis(2-ethylhexyl)dithieno[3,2-b:2′,3′-d]silole)-2,6-diyl-alt-(2,1,3-benzothiadiazole)-4,7-diyl] (PSiBTBT) and poly[(4,4′-bis(2-ethylhexyl)dithieno[3,2-b:2′,3′-d]germole)-2,6-diyl-alt-(2,1,3-benzothiadiazole)-4,7-diyl] (PGeBTBT), are studied. The optoelectronic and charge transport properties of these polymers are investigated with a particular focus on their use for organic photovoltaic (OPV) devices in blends with phenyl-C70-butyric acid methyl ester (PC70BM). It is found that the longer C-Ge bond length, in comparison to C-Si, modifies the molecular conformation and leads to a more planar chain conformation in PGeBTBT than PSiBTBT. This increase in molecular planarity leads to enhanced crystallinity and an increased preference for a face-on backbone orientation, thus leading to higher charge carrier mobility in the diode configuration. These results provide important insight into the impact of the heavy atom substitution on the molecular packing and device performance of polymers based on the poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b]-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole) (PCPDTBT) backbone.
Blakesley JC, Castro FA, Kylberg W, et al., 2014, Towards reliable charge-mobility benchmark measurements for organic semiconductors, ORGANIC ELECTRONICS, Vol: 15, Pages: 1263-1272, ISSN: 1566-1199
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- Citations: 226
Bailey J, Wright EN, Wang X, et al., 2014, Understanding the role of ultra-thin polymeric interlayers in improving efficiency of polymer light emitting diodes, JOURNAL OF APPLIED PHYSICS, Vol: 115, ISSN: 0021-8979
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- Citations: 15
Vaklev NL, Müller R, Muir BVO, et al., 2014, High-Performance Flexible Bottom-Gate Organic Field-Effect Transistors with Gravure Printed Thin Organic Dielectric, Advanced Materials Interfaces
Gravure-printed dielectric films are presented, which are 100-nm thick, have about 1-nm root mean-square surface roughness and show high electric field strength (>300 MV/m). This dielectric is combined with an ultra-thin—less than 10 nm—layer of poly(α-methylstyrene) on top which gives state-of-the-art field-effect mobility in transistors with thermally-evaporated pentacene (0.6 cm2/Vs) and zone-cast TIPS-pentacene (0.3 cm2/Vs).
Razzell-Hollis J, Wade J, Tsoi WC, et al., 2014, Photochemical stability of high efficiency PTB7:PC<sub>70</sub>BM solar cell blends, JOURNAL OF MATERIALS CHEMISTRY A, Vol: 2, Pages: 20189-20195, ISSN: 2050-7488
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- Citations: 126
Wood S, Garnett O, Tokmoldin N, et al., 2014, <i>In situ</i> formation of organic-inorganic hybrid nanostructures for photovoltaic applications, FARADAY DISCUSSIONS, Vol: 174, Pages: 267-279, ISSN: 1359-6640
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- Citations: 3
Beatrup D, Wade J, Biniek L, et al., 2014, Polaron stability in semiconducting polymer neat films, CHEMICAL COMMUNICATIONS, Vol: 50, Pages: 14425-14428, ISSN: 1359-7345
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- Citations: 14
Hodgkiss J, Conboy G, Hutchings G, et al., 2014, Organic photovoltaics and energy: general discussion, FARADAY DISCUSSIONS, Vol: 174, Pages: 341-355, ISSN: 1359-6640
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- Citations: 1
Kim J-H, Song CE, Shin N, et al., 2013, High-Crystalline Medium-Band-Gap Polymers Consisting of Benzodithiophene and Benzotriazole Derivatives for Organic Photovoltaic Cells, ACS APPLIED MATERIALS & INTERFACES, Vol: 5, Pages: 12820-12831, ISSN: 1944-8244
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- Citations: 61
Combe CMS, James DT, Wade J, et al., 2013, Synthesis and morphology of asymmetric, alkyne-functionalised pentacene and 2-fluoroanthradithiophene, TETRAHEDRON LETTERS, Vol: 54, Pages: 6814-6818, ISSN: 0040-4039
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- Citations: 1
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