| 11. |
- Ouyang, Liangqi, et al.
(författare)
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Imaging the Phase Separation Between PEDOT and Polyelectrolytes During Processing of Highly Conductive PEDOT:PSS Films
- 2015
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Ingår i: ACS Applied Materials and Interfaces. - : AMER CHEMICAL SOC. - 1944-8244 .- 1944-8252. ; 7:35, s. 19764-19773
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Tidskriftsartikel (refereegranskat)abstract
- Treating PEDOT:PSS (Clevios) with certain additives, such as ethylene glycol (EG), dimethyl sulfoxide (DMSO) and sorbitol, has been shown to increase the conductivity of this material from roughly 1 to nearly 1000 S/cm. Using a slow drying method, we show that the additive induced a separation between free PSS and reorganized PEDOT:PSS complexes in the highly conductive PEDOT:PSS films. Additives (DMSO, DEG, and PEG 400) were included in PEDOT:PSS aqueous dispersions at large volume fractions. The mixtures were slowly dried under room conditions. During drying, the evaporation of water resulted in an additive-rich solvent mixture from which the reorganized PEDOT:PSS complexes aggregated " into a dense film while free PSS remained in the solution. Upon complete drying, PSS formed a transparent rim film around the conducting PEDOT film. The chemical compositions of the two phases were studied using an infrared microscope. This removal of PSS resulted in more compact packing of PEDOT molecules, as confirmed by X-ray diffraction measurements. X-ray photoelectron spectroscopy and atomic force microscope measurements suggested the enrichment of PEDOT on the film surface after PSS separation. Through a simple drying process in an additive-containing dispersion, the conductivity of PEDOT films increased from 0.1 to 200-400 S/cm. Through this method, we confirmed the existence of two phases in additive-treated and highly conductive PEDOT:PSS films. The proper separation between PSS and PEDOT will be of relevance in designing strategies to process high-performance plastic electrodes.
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| 12. |
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| 13. |
- Ouyang, Liangqi, et al.
(författare)
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The contraction of PEDOT films formed on a macromolecular liquid-like surface
- 2018
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Ingår i: Journal of Materials Chemistry C. - : ROYAL SOC CHEMISTRY. - 2050-7526 .- 2050-7534. ; 6:3, s. 654-660
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Tidskriftsartikel (refereegranskat)abstract
- Vapour phase polymerized (VPP) PEDOT obtained using triblock copolymer PEG-PPG-PEG: Fe(III) tosylate polymeric oxidative layers has shown record-high conductivity and unique thermoelectric properties. These properties are related to the molecular weight, morphology and doping of PEDOT. Here we show that in its unwashed condition, the PEDOT chain adopts a neutral benzenoid conformation. The polymer chain converts into the charged quinoid structure after the removal of oxidizers with solvent washing. X-ray diffraction results suggest that the dopant is also incorporated into the packed polymer after the washing process. The changes in the chain structure and doping lead to the characteristic polaron and bipolaron absorption in the 800 and 1200 nm range. We observed a large contraction of the film after washing that is likely due to these changes, along with the removal of excessive polymer: oxidizer trapped in the PEDOT matrix. The contraction of films can be completely suppressed by mechanical clamping. PEDOT films without contraction show both a higher conductivity and higher optical transparency.
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| 14. |
- Ponseca, Carlito, et al.
(författare)
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Terahertz Helical Antenna Based on Celery Stalks
- 2019
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Ingår i: International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz. - : IEEE Computer Society. - 9781538682852 - 9781538682869
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Konferensbidrag (refereegranskat)abstract
- Cellulose-based helices retrieved from the plant celery with a conductive poly(4-(2,3-dihydrothieno [3,4-b]-[1,4]dioxin-2-yl-methoxy)-1-butanesulfonate (PEDOT-S). A resonance close to 1 THz and a broad shoulder that extends to 3.5 THz was obtained, consistent with electromagnetic models. As helical antennas, it was shown that both axial and normal modes are present, which are correlated to the orientation and antenna electrical lengths of the coated helices. This work opens the possibility of designing tunable terahertz antennas through simple control of their dimensions and orientation. © 2019 IEEE.
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| 15. |
- Qian, Deping, et al.
(författare)
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Design rules for minimizing voltage losses in high-efficiency organic solar cells
- 2018
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Ingår i: Nature Materials. - : NATURE PUBLISHING GROUP. - 1476-1122 .- 1476-4660. ; 17:8, s. 703-
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Tidskriftsartikel (refereegranskat)abstract
- The open-circuit voltage of organic solar cells is usually lower than the values achieved in inorganic or perovskite photovoltaic devices with comparable bandgaps. Energy losses during charge separation at the donor-acceptor interface and non-radiative recombination are among the main causes of such voltage losses. Here we combine spectroscopic and quantum-chemistry approaches to identify key rules for minimizing voltage losses: (1) a low energy offset between donor and acceptor molecular states and (2) high photoluminescence yield of the low-gap material in the blend. Following these rules, we present a range of existing and new donor-acceptor systems that combine efficient photocurrent generation with electroluminescence yield up to 0.03%, leading to non-radiative voltage losses as small as 0.21 V. This study provides a rationale to explain and further improve the performance of recently demonstrated high-open-circuit-voltage organic solar cells.
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| 16. |
- Qu, Jing, et al.
(författare)
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Stiffness, strength and adhesion characterization of electrochemically deposited conjugated polymer films
- 2016
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Ingår i: Acta Biomaterialia. - : ELSEVIER SCI LTD. - 1742-7061 .- 1878-7568. ; 31, s. 114-121
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Tidskriftsartikel (refereegranskat)abstract
- Conjugated polymers such as poly(3,4-ethylenedioxythiphene) (PEDOT) are of interest for a variety of applications including interfaces between electronic biomedical devices and living tissue. The mechanical properties, strength, and adhesion of these materials to solid substrates are all vital for long-term applications. We have been developing methods to quantify the mechanical properties of conjugated polymer thin films. In this paper, the stiffness, strength and the interfacial shear strength (adhesion) of electrochemically deposited PEDOT and PEDOT-co-1,3,5-tri[2-(3,4-ethylene dioxythienyl)]-benzene (EPh) were studied. The estimated Youngs modulus of the PEDOT films was 2.6 +/- 1.4 GPa, and the strain to failure was around 2%. The tensile strength was measured to be 56 +/- 27 MPa. The effective interfacial shear strength was estimated with a shear-lag model by measuring the crack spacing as a function of film thickness. For PEDOT on gold/palladium-coated hydrocarbon film substrates an interfacial shear strength of 0.7 +/- 0.3 MPa was determined. The addition of 5 mole% of a tri-functional EDOT crosslinker (EPh) increased the tensile strength of the films to 283 +/- 67 MPa, while the strain to failure remained about the same (2%). The effective interfacial shear strength was increased to 2.4 +/- 0.6 MPa. Statement of significance This paper describes methods for estimating the ultimate mechanical properties of electrochemically deposited conjugated polymer (here PEDOT and PEDOT copolymers) films. Of particular interest and novelty is our implementation of a cracking test to quantify the shear strength of the PEDOT thin films on these solid substrates. There is considerable interest in these materials as interfaces between biomedical devices and living tissue, however potential mechanisms and modes of failure are areas of continuing concern, and establishing methods to quantify the strengths of these interfaces are therefore of particular current interest. We are confident that these results will be useful to the broader biological materials community and are worthy of broader dissemination. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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| 17. |
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| 18. |
- Tian, Weiqian, et al.
(författare)
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Layer-by-layer self-assembly of pillared two-dimensional multilayers
- 2019
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Ingår i: Nature Communications. - : Nature Publishing Group. - 2041-1723. ; 10
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Tidskriftsartikel (refereegranskat)abstract
- We report Layer-by-Layer (LbL) self-assembly of pillared two-dimensional (2D) multilayers, from water, onto a wide range of substrates. This LbL method uses a small molecule, tris(2-aminoethyl) amine (TAEA), and a colloidal dispersion of Ti3C2Tx MXene to LbL self-assemble (MXene/TAEA)(n )multilayers, where n denotes the number of bilayers. Assembly with TAEA results in highly ordered (MXene/TAEA)(n) multilayers where the TAEA expands the interlayer spacing of MXene flakes by only similar to 1 angstrom and reinforces the interconnection between them. The TAEA-pillared MXene multilayers show the highest electronic conductivity of 7.3 x10(4) S m(-1) compared with all reported MXene multilayers fabricated by LbL technique. The (MXene/ TAEA)(n) multilayers could be used as electrodes for flexible all-solid-state supercapacitors delivering a high volumetric capacitance of 583 F cm(-3) and high energy and power densities of 3.0 Wh L-1 and 4400 W L-1, respectively. This strategy enables large-scale fabrication of highly conductive pillared MXene multilayers, and potentially fabrication of other 2D heterostructures.
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| 19. |
- Tian, Weiqian, et al.
(författare)
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Multifunctional Nanocomposites with High Strength and Capacitance Using 2D MXene and 1D Nanocellulose
- 2019
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Ingår i: Advanced Materials. - : WILEY-V C H VERLAG GMBH. - 0935-9648 .- 1521-4095.
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Tidskriftsartikel (refereegranskat)abstract
- The family of two-dimensional (2D) metal carbides and nitrides, known as MXenes, are among the most promising electrode materials for supercapacitors thanks to their high metal-like electrical conductivity and surface-functional-group-enabled pseudocapacitance. A major drawback of these materials is, however, the low mechanical strength, which prevents their applications in lightweight, flexible electronics. A strategy of assembling freestanding and mechanically robust MXene (Ti3C2Tx) nanocomposites with one-dimensional (1D) cellulose nanofibrils (CNFs) from their stable colloidal dispersions is reported. The high aspect ratio of CNF (width of approximate to 3.5 nm and length reaching tens of micrometers) and their special interactions with MXene enable nanocomposites with high mechanical strength without sacrificing electrochemical performance. CNF loading up to 20%, for example, shows a remarkably high mechanical strength of 341 MPa (an order of magnitude higher than pristine MXene films of 29 MPa) while still maintaining a high capacitance of 298 F g(-1) and a high conductivity of 295 S cm(-1). It is also demonstrated that MXene/CNF hybrid dispersions can be used as inks to print flexible micro-supercapacitors with precise dimensions. This work paves the way for fabrication of robust multifunctional MXene nanocomposites for printed and lightweight structural devices.
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| 20. |
- Wang, Chuanfei, 1986-, et al.
(författare)
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Relationship of Ionization Potential and Oxidation Potential of Organic Semiconductor Films Used in Photovoltaics
- 2018
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Ingår i: Solar RRL. - : Wiley-Blackwell. - 2367-198X. ; 2:9
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Tidskriftsartikel (refereegranskat)abstract
- Ultraviolet photoelectron spectroscopy (UPS) and cyclic voltammetry (CV) are employed to measure energy levels for charge transport in organic semiconductor films. A series of classical molecules/polymers used in organic bulk heterojunction solar cells are deposited on platinum substrates/electrodes to form thin films and a linear relationship of vertical ionization potential (IP) measured by UPS and relative oxidation potential (Eox) obtained by CV is found, with a slope equal to unity. The intercept varies with the different reference redox couples and repeated potential sweep numbers during experiment processes. The relationship provides for an easy conversion of values obtained by the two techniques and correlates well with device parameters. The precision in the CV-derived IP values is not sufficient, however, to enable precise design of energy level alignment at heterojunction and the approach does not improve upon the current ?best practice? for obtaining donor ionization potential?acceptor electron affinity gaps at heterojunctions.
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