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  • 51.
    Lanz, Thomas
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sandström, Andreas
    Umeå University, Faculty of Science and Technology, Department of Physics. LunaLEC AB, Tvistevägen 47, PO Box 7970, SE-90719 Umeå, Sweden.
    Tang, Shi
    Umeå University, Faculty of Science and Technology, Department of Physics. LunaLEC AB, Tvistevägen 47, PO Box 7970, SE-90719 Umeå, Sweden.
    Chabrecek, Peter
    Sefar AG.
    Sonderegger, Uriel
    Sefar AG.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics. LunaLEC AB, Tvistevägen 47, PO Box 7970, SE-90719 Umeå, Sweden.
    A light–emission textile device: conformal spray-sintering of a woven fabric electrode2016In: Flexible and Printed Electronics, ISSN 2058-8585, Vol. 1, no 2, article id 025004Article in journal (Refereed)
    Abstract [en]

    We report on the realization of an ultra-flexible, light-weight and large-area emissive textile device. The anode and active material of a light-emitting electrochemical cell (LEC) were deposited by conformal spray-coating of a transparent fabric-based electrode, comprising a weave of fine Ag-coated Cu wires and poly(ethylene naphthalene) monofilament fibers embedded in a polyurethane matrix. The yellow-emitting textile featured low turn-on voltage (5 V), high maximum brightness (>4000 cd m−2), good efficiency (3.4 cd A−1), and reasonable lifetime (180 h at >100 cd m−2). Uniform emission to the eye was attained from thin and highly flexible textiles featuring a large emission area of 42 cm2, without resorting to planarization of the partially wavy-shaped (valley-to-peak height = 2.7 μm) fabric electrode. The key enabling factors for the functional emissive textile are the characteristic in situ electrochemical doping of LEC devices, the 'dry' spray-sintering deposition of the active material, and the attractive mechanical, electronic and optical properties of the fabric-based electrode.

  • 52.
    Larsen, Christian
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Barzegar, Hamid Reza
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Nitze, Florian
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    On the fabrication of crystalline C-60 nanorod transistors from solution2012In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 23, no 34, p. 344015-Article in journal (Refereed)
    Abstract [en]

    Flexible and high-aspect-ratio C-60 nanorods are synthesized using a liquid-liquid interfacial precipitation process. As-grown nanorods are shown to exhibit a hexagonal close-packed single-crystal structure, with m-dichlorobenzene solvent molecules incorporated into the crystalline structure in a C-60:m-dichlorobenzene ratio of 3.2. An annealing step at 200 degrees C transforms the nanorods into a solvent-free face-centred-cubic polycrystalline structure. The nanorods are deposited onto field-effect transistor structures using two solvent-based techniques: drop-casting and dip-coating. We find that dip-coating deposition results in a preferred alignment of non-bundled nanorods and a satisfying transistor performance. The latter is quantified by the attainment of an electron mobility of 0.08 cm(2) V-1 s(-1) and an on/off ratio of >10(4) for a single-crystal nanorod transistor, fabricated with a solution-based and low-temperature process that is compatible with flexible substrates.

  • 53.
    Larsen, Christian
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Forchheimer, Robert
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Tu, Deyu
    Design, fabrication and application of organic power converters: Driving light-emitting electrochemical cells from the AC mains2017In: Organic electronics, ISSN 1566-1199, E-ISSN 1878-5530, Vol. 45, p. 57-64Article in journal (Refereed)
    Abstract [en]

    The design, fabrication and operation of a range of functional power converter circuits, based on diode configured organic field-effect transistors as the rectifying unit and capable of transforming a high AC input voltage to a selectable DC voltage, are presented. The converter functionality is demonstrated by selecting and tuning its constituents so that it can effectively drive a low-voltage organic electronic device, a light-emitting electrochemical cell (LEC), when connected to high-voltage AC mains. It is established that the preferred converter circuit for this task comprises an organic full-wave rectifier and a regulation resistor but is void of a smoothing capacitor, and that such a circuit connected to the AC mains (230 V, 50 Hz) successfully can drive an LEC to bright luminance (360 cd m(-2)) and high efficiency (6.4 cd A(-1)).

  • 54.
    Larsen, Christian
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wang, Jia
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Complementary ring oscillator fabricated via direct laser-exposure and solution-processing of a single-layer organic film2012In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 520, no 7, p. 3009-3012Article in journal (Refereed)
    Abstract [en]

    A complementary ring oscillator is realized by exposing a solution-processed single-layer organic film to area-selective laser-light exposure and solution development. The pristine film comprises a blend of two organic semiconductors: p-type poly(3-hexylthiophene-2,5-diyl) (P3HT) and n-type [6,6]-phenyl C-61 butyric acid methyl ester (PCBM). The exposure transforms PCBM into an insoluble form, and the subsequent development selectively removes the non-exposed PCBM while leaving exposed PCBM and P3HT intact. The 5-step ring oscillator exhibits a frequency of 10 mHz, a power delay product of 2.0 mu J, and an energy delay product of 22 mu Js. Opportunities for performance improvements of the scalable fabrication technique are highlighted in an accompanying analysis.

  • 55.
    Lindh, E. Mattias
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Lundberg, Petter
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Lanz, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Optical analysis of light-emitting electrochemical cells2019In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 9, article id 10433Article in journal (Refereed)
    Abstract [en]

    The light-emitting electrochemical cell (LEC) is a contender for emerging applications of light, primarily because it offers low-cost solution fabrication of easily functionalized device architectures. The attractive properties originate in the in-situ formation of electrochemically doped transport regions that enclose an emissive intrinsic region, but the understanding of how this intricate doping structure affects the optical performance of the LEC is largely lacking. We combine angle- and doping-dependent measurements and simulations, and demonstrate that the emission zone in our high-performance LEC is centered at ~30% of the active-layer thickness (dal) from the anode. We further find that the emission intensity and efficiency are undulating with dal, and establish that the first emission maximum at dal ~ 100 nm is largely limited by the lossy coupling of excitons to the doping regions, whereas the most prominent loss channel at the second maximum at dal ~ 300 nm is wave-guided modes.

  • 56.
    Lindh, E. Mattias
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sandström, Andreas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Inkjet Printed Bilayer Light-Emitting Electrochemical Cells for Display and Lighting Applications2014In: Small, ISSN 1613-6810, E-ISSN 1613-6829, Vol. 10, no 20, p. 4148-4153Article in journal (Refereed)
    Abstract [en]

    A new bilayer light-emitting electrochemical cell (LEC) device, which allows well-defined patterned light emission through an easily adjustable, mask-free, and additive fabrication process, is reported. The bilayer stack comprises an inkjet-printed lattice of micrometer-sized electrolyte droplets, in a filled or patterned lattice configuration. On top of this, a thin layer of light-emitting compound is deposited from solution. The light emission is demonstrated to originate from regions proximate to the interfaces between the inkjetted electrolyte, the light-emitting compound, and one electrode, where bipolar electron/hole injection and electrochemical doping are facilitated by ion motion. By employing KCF3SO3 in poly(ethylene glycol) as the electrolyte, Super Yellow as the light-emitting compound, and two air-stabile electrodes, it is possible to realize filled lattice devices that feature uniform yellow-green light emission to the naked eye, and patterned lattice devices that deliver well-defined and high-contrast static messages with a pixel density of 170 PPI.

  • 57.
    Lindh, Erik Mattias
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sandström, Andreas
    Umeå University, Faculty of Science and Technology, Department of Physics. LunaLEC AB, Umeå, Sweden .
    Andersson, Mats Roland
    University of South Australia.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics. LunaLEC AB, Umeå, Sweden .
    Luminescent line art by direct-write patterning2016In: Light: Science & Applications, ISSN 2047-7538, Vol. 5, article id e16050Article in journal (Refereed)
    Abstract [en]

    We present a direct-write patterning method for the realization of electroluminescent (EL) line art using a surface-emissive light-emitting electrochemical cell with its electrolyte and EL material separated into a bilayer structure. The line-art emission isachieved through subtractive patterning of the electrolyte layer with a stylus, and the single-step patterning can be either manual for personalization and uniqueness or automated for high throughput and repeatability. We demonstrate that the light emission is effectuated by cation-assisted electron injection in the patterned regions and that the resulting emissive lines can be as narrow as a few micrometers. The versatility of the method is demonstrated through the attainment of a wide range of light-emission patterns and colors using a variety of different materials. We propose that this low-voltage-driven and easy-to-modify luminescent line-art technology could be of interest for emerging applications, such as active packaging and personalized gadgets.

  • 58.
    Lundberg, Petter
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Lindh, Mattias
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Tang, Shi
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Toward Efficient and Metal-Free Emissive Devices: A Solution Processed Host Guest Light-Emitting Electrochemical Cell Featuring Thermally Activated Delayed Fluorescence2017In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 9, no 34, p. 28810-28816Article in journal (Refereed)
    Abstract [en]

    The next generation of emissive devices should preferably be efficient, low-cost, and environmentally sustainable, and as such utilize all electrically generated excitons (both singlets and triplets) for the light emission, while being free from rare metals such as iridium. Here, we report on a step toward this vision through the design, fabrication, and operation of a host guest light-emitting electrochemical cell (LEC) featuring an organic thermally activated delayed fluorescence (TADF) guest that harvests both singlet and triplet excitons for the emission. The rare-metal-free active material also consists of a polymeric electrolyte and a polymeric compatibilizer for the facilitation of a cost-efficient and scalable solution-based fabrication, and for the use of air-stable electrodes. We report that such TADF-LEC devices can deliver uniform green light emission with a maximum luminance of 228 cd m(-2) when driven by a constant-current density of 770 A m(-2), and 760 cd m(-2) during a voltage ramp, which represents a one-order-of-magnitude improvement in comparison to previous TADF-emitting LECs.

  • 59.
    Matyba, Piotr
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Andersson, Mats R.
    Department of Polymer Technology, Chalmers University of Technology, SE-412 96 Göteborg, Sweden.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    On the desired properties of a conjugated polymer-electrolyte blend in a light-emitting electrochemical cell2008In: Organic electronics, ISSN 1566-1199, E-ISSN 1878-5530, Vol. 9, no 5, p. 699-710Article in journal (Refereed)
  • 60.
    Matyba, Piotr
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Maturova, Klara
    Eindhoven University of Technology.
    Kemerink, Martijn
    Eindhoven University of Technology.
    Robinson, Nathaniel
    Department of Physics, Chemistry and Biology, Linköping University, Sweden .
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    The dynamic organic p-n junction2009In: Nature Materials, ISSN 1476-1122, E-ISSN 1476-4660, Vol. 8, no 8, p. 672-676Article in journal (Refereed)
  • 61.
    Matyba, Piotr
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Yamaguchi, Hisato
    Rutgers University.
    Chhowalla, Manish
    Rutgers University.
    Robinson, Nathaniel D.
    Linköpings universitet.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Flexible and Metal-Free Light-Emitting Electrochemical Cells Based on Graphene and PEDOT-PSS as the Electrode Materials2011In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 5, no 1, p. 574-580Article in journal (Refereed)
    Abstract [en]

    We report flexible and metal-free light-emitting electrochemical cells (LECs) using exclusively solution-processed organic materials and illustrate interesting design opportunities offered by such conformable devices with transparent electrodes. Flexible LEC devices based on chemically derived graphene (CDG) as the cathode and poly(3,4-ethylenedioxythiophene) mixed with poly(styrenesulfonate) as the anode exhibit a low turn-on voltage for yellow light emission (V = 2.8 V) and a good efficiency 2.4 (4.0) cd/A at a brightness of 100 (50) cd/m2. We also find that CDG is electrochemically inert over a wide potential range (+1.2 to −2.8 V vsferrocene/ferrocenium) and exploit this property to demonstrate planar LEC devices with CDG as both the anode and the cathode.

  • 62.
    Matyba, Piotr
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Yamaguchi, Hisato
    Rutgers University.
    Eda, Goki
    Rutgers University.
    Chhowalla, Manish
    Rutgers University.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Robinson, Nathaniel D.
    Linköpings universitet.
    Graphene and mobile ions: the key to all-plastic, solution-processed light-emitting devices2010In: ACS Nano, ISSN 1936-0851, Vol. 4, no 2, p. 637-642Article in journal (Refereed)
    Abstract [en]

    The emerging field of “organic” or “plastic” electronics has brought low-voltage, ultrathin, and energy-efficient lighting and displays to market as organic light-emitting diode (OLED) televisions and displays in cameras and mobile phones. Despite using carbon-based materials as the light-emitting layer, previous efficient organic electronic light-emitting devices have required at least one metal electrode. Here, we utilize chemically derived graphene for the transparent cathode in an all-plastic sandwich-structure device, similar to an OLED, called a light-emitting electrochemical cell (LEC). Using a screen-printable conducting polymer as a partially transparent anode and a micrometer-thick active layer solution-deposited from a blend of a light-emitting polymer and a polymer electrolyte, we demonstrate a light-emitting device based solely on solution-processable carbon-based materials. Our results demonstrate that low-voltage, inexpensive, and efficient light-emitting devices can be made without using metals. In other words, electronics can truly be “organic”.

  • 63. McRae, Edward
    et al.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Physics.
    Hérold, A.
    Lelaurain, Michelle
    Marêché, Jean-Francois
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    C-axis transport studies and in-plane intercalate layer structure in sodium halide intercalated graphite1998In: Extended Abstracts of Eurocarbon´98, European Conference Science and Technology of Carbon, Strasbourg 1998, volume 2, Deutsche Keramische Gesellschaft, Arbeitskreis Kohlenstoff , 1998, p. 767-768Conference paper (Other academic)
  • 64.
    Mindemark, Jonas
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Illuminating the electrolyte in light-emitting electrochemical cells2016In: Journal of Materials Chemistry C, ISSN 2050-7526, E-ISSN 2050-7534, Vol. 4, no 3, p. 420-432Article, review/survey (Refereed)
    Abstract [en]

    Light-emitting electrochemical cells (LECs) convert electric current to light within an active material comprising an electroluminescent organic semiconductor and an electrolyte. It is well established that it is the presence of this electrolyte that enabled the recent development of low-cost fabrication methods of functional LECs as well as the realisation of unique device architectures. At the same time, it should be acknowledged that the current lower performance of LECs in comparison to the more commonplace organic light-emitting diode, at least in part, is intimately linked to the utilisation of non-ideal electrolytes. In this review, we present the tasks that the electrolyte should fulfil during the various stages of LEC operation, and how the characteristics of the electrolyte can affect the LEC performance, specifically the turn-on time, the efficiency and the operational stability. We thereafter introduce the different classes of electrolytes that have been implemented in LEC devices up to date, and discuss how these electrolytes have been able to meet the specific requirements of the LEC technology.

  • 65.
    Mindemark, Jonas
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. Department of Chemistry, Ångström Laboratory, Uppsala University.
    Tang, Shi
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Li, Hu
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ion Transport beyond the Polyether Paradigm: Introducing Oligocarbonate Ion Transporters for Efficient Light-Emitting Electrochemical Cells2018In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 28, no 32, article id 1801295Article in journal (Refereed)
    Abstract [en]

    The light-emitting electrochemical cell (LEC) is fundamentally dependent on mobile ions for its operation. In polymer LECs, the mobile ions are commonly provided by dissolving a salt in an ion transporter, with the latter almost invariably being an ether-based compound. Here, the synthesis, characterization, and application of a new class of carbonate-based ion transporters are reported. A polymer LEC, comprising a star-branched oligocarbonate endowed with aliphatic side groups as the ion transporter, features a current efficacy of 13.8 cd A(-1) at a luminance of 1060 cd m(-2), which is a record-high efficiency/luminance combination for a singlet-emitting LEC. It is further established that the design principles of a high-performance carbonate ion transporter constitute the selection of an oligomeric structure over a corresponding polymeric structure and the endowment of the oligomer with functional side chains to render it compatible with the polymeric emitter.

  • 66.
    Mindemark, Jonas
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Tang, Shi
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wang, Jia
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Kaihovirta, Nikolai
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Brandell, Daniel
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    High-Performance Light-Emitting Electrochemical Cells by Electrolyte Design2016In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 28, no 8, p. 2618-2623Article in journal (Refereed)
    Abstract [en]

    Polymer light-emitting electrochemical cells (LECs) are inherently dependent on a suitable electrolyte for proper function. Here, we design and synthesize a series of alkyl carbonate-capped star-branched oligoether-based electrolytes with large electrochemical stability windows, facile ion release, and high compatibility with common light-emitting materials. LECs based on such designed electrolytes feature fast turn-on, a long operational lifetime of 1400 h at >100 cd m(-2) and a record-high power conversion efficiency of 18.1 lm W-1, when equipped with an external outcoupling film.

  • 67.
    Modestov, Mikhail
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Bychkov, Vitaly
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Brodin, Gert
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Valiev, Damir
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Marklund, Mattias
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Matyba, Piotr
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Model of the electrochemical conversion of an undoped organic semiconductor film to a doped conductor film.2010In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, no 8, p. 081203(R)-Article in journal (Refereed)
    Abstract [en]

    We develop a model describing the electrochemical conversion of an organic semiconductor (specifically, the active material in a light-emitting electrochemical cell) from the undoped nonconducting state to the doped conducting state. The model, an extended Nernst-Planck-Poisson model, takes into account both strongly concentration-dependent mobility and diffusion for the electronic charge carriers and the Nernst equation in the doped conducting regions. The standard Nernst-Planck-Poisson model is shown to fail in its description of the properties of the doping front. Solving our extended model numerically, we demonstrate that doping front progression in light-emitting electrochemical cells can be accurately described.

  • 68.
    Munar, Antoni
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sandström, Andreas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Tang, Shi
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Shedding light on the operation of polymer light-emitting electrochemical cells using impedance spectroscopy2012In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 22, no 7, p. 1511-1517Article in journal (Refereed)
    Abstract [en]

    A combination of impedance spectroscopy, device characterization, and modeling is used to pinpoint key processes in the operation of polymer light-emitting electrochemical cells (LECs). At low applied voltage, electric double layers with a thickness of similar to 23 nm are shown to exist at the electrode interfaces. At voltages exceeding the bandgap potential of the conjugated polymer (V = 2.5 V for superyellow), a light-emitting pn junction forms in situ, with a steady-state structure that is found to depend strongly on the applied voltage. This is exemplified by that the effective pn junction thickness (dpn) for a device with an interelectrode gap of 90 nm decreases from similar to 23 nm at 2.5 V to similar to 6 nm at 3.9 V. The current increases with decreasing dpn in a concerted manner, while the brightness reaches its peak at V = 3.4 V when dpn similar to 10 nm. The existence of an optimum dpn for high brightness in LECs is attributed to an offset between an increase in the exciton formation rate with decreasing dpn, due to an increasing current, and a simultaneous decrease in the exciton radiative decay rate, when an increasing fraction of excitons diffuses away from the pn junction into the surrounding non-radiative doping regions.

  • 69. Murto, Petri
    et al.
    Tang, Shi
    Umeå University, Faculty of Science and Technology, Department of Physics. LunaLEC AB, Umeå University, SE-90187 Umeå, Sweden.
    Larsen, Christian
    Umeå University, Faculty of Science and Technology, Department of Physics. LunaLEC AB, Umeå University, SE-90187 Umeå, Sweden.
    Xu, Xiaofeng
    Sandström, Andreas
    Pietarinen, Juuso
    Bagemihl, Benedikt
    Abdulahi, Birhan A.
    Mammo, Wendimagegn
    Andersson, Mats R.
    Wang, Ergang
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics. LunaLEC AB, Umeå University, SE-90187 Umeå, Sweden.
    Incorporation of Designed Donor-Acceptor-Donor Segments in a Host Polymer for Strong Near-Infrared Emission from a Large-Area Light-Emitting Electrochemical Cell2018In: ACS Applied Energy Materials, ISSN 2574-0962, Vol. 1, no 4, p. 1753-1761Article in journal (Refereed)
    Abstract [en]

    Cost-efficient thin-film devices that emit in the near-infrared (NIR) range promise a wide range of important applications. Here, the synthesis and NIR application of a series of copolymers comprising poly[indacenodithieno[3,2-b]thiophene-2,8-diyl] (PIDTT) as the host and different donor–acceptor–donor (DAD) segments as the guest are reported. We find that a key design criterion for efficient solid-state host-to-guest energy transfer is that the DAD conformation is compatible with the conformation of the host. Such host–guest copolymers are evaluated as the emitter in light-emitting electrochemical cells (LECs) and organic light-emitting diodes, and the best performance is invariably attained from the LEC devices because of the observed balanced electrochemical doping that alleviates issues with a noncentered emission zone. An LEC device comprising a host–guest copolymer with 4,4-bis(2-ethylhexyl)-4H-silolo[3,2-b:4,5-b′]dithiophene as the donor and benzo[c][1,2,5]thiadiazole as the acceptor delivers an impressive near-infrared (NIR) performance in the form of a high radiance of 1458 μW/cm2 at a peak wavelength of 725 nm when driven by a current density of 500 mA/cm2, a second-fast turn-on, and a good stress stability as manifested in a constant radiance output during 3 days of uninterrupted operation. The high-molecular-weight copolymer features excellent processability, and the potential for low-cost and scalable NIR applications is verified through a spray-coating fabrication of a >40 cm2 large-area device, which emits intense and uniform NIR light at a low drive voltage of 4.5 V.

  • 70. Murto, Petri
    et al.
    Tang, Shi
    Umeå University, Faculty of Science and Technology, Department of Physics. LunaLEC AB, Umeå University, Umeå, Sweden.
    Larsen, Christian
    Umeå University, Faculty of Science and Technology, Department of Physics. LunaLEC AB, Umeå University, Umeå, Sweden.
    Xu, Xiaofeng
    Sandström, Andreas
    LunaLEC AB, Umeå University, Umeå, Sweden.
    Pietarinen, Juuso
    Bagemihl, Benedikt
    Abdulahi, Birhan A.
    Mammo, Wendimagegn
    Andersson, Mats R.
    Wang, Ergang
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics. LunaLEC AB, Umeå University, Umeå, Sweden.
    Incorporation of Designed Donor-Acceptor-Donor Segments in a Host Polymer for Strong Near-Infrared Emission from a Large-Area Light-Emitting Electrochemical Cell2018In: ACS Applied Energy Materials, ISSN 2574-0962, Vol. 1, no 4, p. 1753-1761Article in journal (Refereed)
    Abstract [en]

    Cost-efficient thin-film devices that emit in the near infrared (NIR) range promise a wide range of important applications. Here, the synthesis and NIR application of a series of copolymers comprising poly[indacenodithieno[3,2-b]thiophene-2,8-diyl] (PIDTT) as the host and different donor acceptor donor (DAD) segments as the guest are reported. We find that a key design criterion for efficient solid-state host-to-guest energy transfer is that the DAD conformation is compatible with the conformation of the host. Such host guest copolymers are evaluated as the emitter in light-emitting electrochemical cells (LECs) and organic light-emitting diodes, and the best performance is invariably attained from the LEC devices because of the observed balanced electrochemical doping that alleviates issues with a noncentered emission zone. An LEC device comprising a host guest copolymer with 4,4-bis(2-ethylhexyl)-4H-silolo[3,2-b:4,5-b']dithiophene as the donor and benzo[c][1,2,5]thiadiazole as the acceptor delivers an impressive near-infrared (NIR) performance in the form of a high radiance of 1458 mu W/cm(2) at a peak wavelength of 725 nm when driven by a current density of 500 mA/cm(2), a second-fast turn-on, and a good stress stability as manifested in a constant radiance output during 3 days of uninterrupted operation. The high-molecular-weight copolymer features excellent processability, and the potential for low-cost and scalable NIR applications is verified through a spray-coating fabrication of a >40 cm(2) large-area device, which emits intense and uniform NIR light at a low drive voltage of 4.5 V.

  • 71. Ortony, Julia
    et al.
    Yang, Reiquyang
    Brzezinski, Jacek
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Physics.
    Nguyen, Thuq
    Bazan, Guillermo
    Thermal Properties of Conjugated Polyelectrolytes.2008In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 20, no 2, p. 298-302Article in journal (Refereed)
  • 72.
    Orädd, Greger
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Edman, Ludvig
    Physics.
    Ferry, Anders
    Umeå University, Faculty of Science and Technology, Chemistry.
    Diffusion: a comparision between liquid and solid polymer LiTFSI electrolytes2001In: 13th International Conference on Solid State Ionics (8-14 July 2001), Cairns, AUSTRALIA, 2001Conference paper (Refereed)
    Abstract [en]

    From careful analyses of pfg-NMR data, it is demonstrated that the size of the diffusing Li+·xH2O complex in an aqueous solution of LiTFSI is strongly dependent on salt concentration, with the number of solvating water units ranging from six in dilute (H2O)500LiTFSI to two in highly concentrated (H2O)5LiTFSI. Such a relationship is explained by a mass tendency toward a lower solvation number as the number of available H2O molecules per lithium ion decreases. In a liquid (PEO)nLiTFSI system, a contrasting situation prevails, since the size of the diffusing Li+ complex is almost constant over a large salt concentration range (5≤n≤50). Our interpretations of these data imply that one PEO chain, containing on average nine ether oxygen units, is able to dissolve up to two lithium ions, but exclude the possibility of cationic crosslinks between different PEO chains and direct ionic interactions. For solid P(EO)nLiTFSI eletrolytes, a significantly lower value for the diffusion coefficient of the small lithium ions as compared to that of the large TFSI ions (DLi=0.2DTFSI) was found for all salt concentrations investigated (5≤n≤50). This observation fits in with recent structural observations, which suggest that lithium ions move as single entities in this specific system and require a rather complicated solvation–desolvation step for long-range motion. In all electrolytes investigated, both liquid and solid, the large and bulky TFSI ion appears to be moving as a single unit, thus manifesting the excellent ionization properties of the LiTFSI salt.

  • 73.
    Orädd, Greger
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Edman, Ludvig
    Physics.
    Ferry, Anders
    Physics.
    Diffusion: a comparison between liquid and solid polymer LiTFSI electrolytes2002In: Solid State Ionics, Vol. 152-153, p. 131-6Article in journal (Refereed)
    Abstract [en]

    From careful analyses of pfg-NMR data, it is demonstrated that the size of the diffusing Li+·xH2O complex in an aqueous solution of LiTFSI is strongly dependent on salt concentration, with the number of solvating water units ranging from six in dilute (H2O)500LiTFSI to two in highly concentrated (H2O)5LiTFSI. Such a relationship is explained by a mass tendency toward a lower solvation number as the number of available H2O molecules per lithium ion decreases. In a liquid (PEO)nLiTFSI system, a contrasting situation prevails, since the size of the diffusing Li+ complex is almost constant over a large salt concentration range (5≤n≤50). Our interpretations of these data imply that one PEO chain, containing on average nine ether oxygen units, is able to dissolve up to two lithium ions, but exclude the possibility of cationic crosslinks between different PEO chains and direct ionic interactions. For solid P(EO)nLiTFSI eletrolytes, a significantly lower value for the diffusion coefficient of the small lithium ions as compared to that of the large TFSI ions (DLi=0.2DTFSI) was found for all salt concentrations investigated (5≤n≤50). This observation fits in with recent structural observations, which suggest that lithium ions move as single entities in this specific system and require a rather complicated solvation–desolvation step for long-range motion. In all electrolytes investigated, both liquid and solid, the large and bulky TFSI ion appears to be moving as a single unit, thus manifesting the excellent ionization properties of the LiTFSI salt.

  • 74. Robinson, Nate D.
    et al.
    Fang, Junfeng
    Umeå University, Faculty of Science and Technology, Physics.
    Matyba, Piotr
    Umeå University, Faculty of Science and Technology, Physics.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Physics.
    Electrochemical doping during light emission in polymer light-emitting electrochemical cells2008In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 78, no 24, p. 245202-Article in journal (Refereed)
  • 75. Robinson, Nathaniel D.
    et al.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Chhowalla, Manish
    Graphene electrodes for organic metal-free light-emitting devices2012In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T146, p. 014023-Article in journal (Refereed)
    Abstract [en]

    In addition to its fascinating electrical and mechanical properties, graphene is also an electrochemically stable and transparent electrode material. We demonstrate its applicability as both anode and cathode in a light-emitting electrochemical cell (LEC), an electrochemical analogue to a polymer organic light-emitting diode. Specifically, we summarize recent progress in carbon-based metal-free light-emitting devices enabled by chemically derived graphene cathodes on quartz and plastic substrates, and explain the advantages of using LECs in manufacturing large-area devices.

  • 76.
    Robinson, Nathaniel D
    et al.
    Linköpings universitet.
    Matyba, Piotr
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    A light-emitting electrochemical device, a system comprising such a device and use of such a device2011Patent (Other (popular science, discussion, etc.))
  • 77. Robinson, N.D.
    et al.
    Shin, Joon-Ho
    Umeå University, Faculty of Science and Technology, Physics.
    Berggren, Magnus
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Physics.
    Doping Front Propagation in Light-Emitting Electrochemical Cells2006In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 74, no 15, p. 155210-Article in journal (Refereed)
  • 78.
    Sandström, Andreas
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Asadpoordarvish, Amir
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Enevold, Jenny
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Spraying Light: Ambient-Air Fabrication of Large-Area Emissive Devices on Complex-Shaped Surfaces2014In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 26, no 29, p. 4975-4980Article in journal (Refereed)
    Abstract [en]

    Light-emitting electrochemical cells, featuring uniform and efficient light emission over areas of 200 cm(2), are fabricated under ambient air with a for-the-purpose developed "spray-sintering" process. This fault-tolerant fabrication technique can also produce multicolored emission patterns via sequential deposition of different inks based on identical solvents. Significantly, additive spray-sintering using a mobile airbrush allows a straightforward addition of emissive function onto a wide variety of complex-shaped surfaces, as exemplified by the realization of a light-emitting kitchenware fork.

  • 79.
    Sandström, Andreas
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Dam, Henrik F.
    Krebs, Frederik C.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ambient fabrication of flexible and large-area organic light-emitting devices using slot-die coating2012In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 3, p. 1002-Article in journal (Refereed)
    Abstract [en]

    The grand vision of manufacturing large-area emissive devices with low-cost roll-to-roll coating methods, akin to how newspapers are produced, appeared with the emergence of the organic light-emitting diode about 20 years ago. Today, small organic light-emitting diode displays are commercially available in smartphones, but the promise of a continuous ambient fabrication has unfortunately not materialized yet, as organic light-emitting diodes invariably depend on the use of one or more time-and energy-consuming process steps under vacuum. Here we report an all-solution-based fabrication of an alternative emissive device, a light-emitting electrochemical cell, using a slot-die roll-coating apparatus. The fabricated flexible sheets exhibit bidirectional and uniform light emission, and feature a fault-tolerant >1-mu m-thick active material that is doped in situ during operation. It is notable that the initial preparation of inks, the subsequent coating of the constituent layers and the final device operation all could be executed under ambient air.

  • 80.
    Sandström, Andreas
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Towards High-Throughput Coating and Printing of Light-Emitting Electrochemical Cells: A Review and Cost Analysis of Current and Future Methods2015In: Energy Technology, ISSN 2194-4288, Vol. 3, no 4, p. 329-339Article, review/survey (Refereed)
    Abstract [en]

    A revolution is ongoing in the field of artificial light emission, with two prime examples being the quickly growing application of the energy-efficient light-emitting diode (LED) in illumination and the introduction of the high-contrast organic LED (OLED) display in various handheld appliances. It is anticipated that the next big breakthrough will constitute the emergence of a true low-cost technology, which features novel and attractive form factors such as flexibility, light-weight, and large-area emission. To realize this challenging vision, it is mandatory to identify an emissive technology that can be fabricated in a low-energy and material-conservative manner. In this context, recent demonstrations of a roll-to-roll (R2R) compatible coating and printing of thin-film light-emitting electrochemical cells (LECs) on flexible substrates are highly interesting. Here, we review these achievements, and perform a first analysis of the merits of different LEC fabrication methods with regard to material consumption, capital investment, running cost, and throughput. Among our findings we mention a fault-tolerant, small-volume batch fabrication of LEC devices using spray sintering, which can be executed at a low installment cost of 100000Euro, but where the large-area devices currently carry a fabrication cost tag of 14000Eurom(-2). The true appeal of the technology is, therefore, better visualized in the high-volume R2R-coating scenario, for which the installment cost is 20times higher, but where the projected price tag is much more attractive (11Euro per m(2)). If such flexible and light-weight (and potentially metal-free) sheets are driven at a luminance of 1000cdm(-2), the cost per lumen is a mere 0.0036Eurolm(-1), which is one order of magnitude lower than the projected future costs for LEDs and OLEDs.

  • 81.
    Sandström, Andreas
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Matyba, Piotr
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Yellow-green light-emitting electrochemical cells with long lifetime and high efficiency2010In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 96, no 5, p. 053303-Article in journal (Refereed)
    Abstract [en]

     We show that the electrochemical stability window of the constituent components in light-emitting electrochemical cells (LECs), e.g., the electrolyte, should be considered in order to minimize undesired side reactions. By designing and operating LECs in accordance with straightforward principles, we demonstrate sandwich cells that turn on fast at room temperature (<2 s), and which emit significant yellow-green light (>100 cd/m2) during 25 days of uninterrupted operation at low voltage (<4 V) and high power conversion efficacy ~6 lm/W. We further demonstrate that it is possible to attain balanced p- and n-type doping and a centered p-n junction in such planar LECs based on the conjugated polymer “superyellow.”

  • 82.
    Sandström, Andreas
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Matyba, Piotr
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Inganäs, Olle
    Linköpings universitet.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Separating ion and and electron transport: the bi-layer light-emitting electrochemical cell2010In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 132, no 19, p. 6646-6647Article in journal (Refereed)
    Abstract [en]

    The current generation of polymer light-emitting electrochemical cells (LECs) suffers from insufficient stability during operation. One identified culprit is the active material, which comprises an intimate blend between an ion-conducting electrolyte and an electron-transporting conjugated polymer, as it tends to undergo phase separation during long-term operation and the intimate contact between the ion- and electron-transporting components provokes side reactions. To address these stability issues, we present here a bilayer LEC structure in which the electrolyte is spatially separated from the conjugated polymer. We demonstrate that employing this novel device structure, with its clearly separated ion- and electron-transport paths, leads to distinctly improved LEC performance in the form of decreased turn-on time and improved light emission. We also point out that it will allow for the utilization of combinations of active materials having mutually incompatible solubilities.

  • 83. Shafikov, Marsel Z.
    et al.
    Tang, Shi
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Larsen, Christian
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Bodensteiner, Michael
    Kozhevnikov, Valery N.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    An efficient heterodinuclear Ir(III)/Pt(II) complex: synthesis, photophysics and application in light-emitting electrochemical cells2019In: Journal of Materials Chemistry C, ISSN 2050-7526, E-ISSN 2050-7534, Vol. 7, no 34, p. 10672-10682Article in journal (Refereed)
    Abstract [en]

    We report on the design, synthesis, characterization and successful application of a heterodinuclear Ir(III)/Pt(II) complex endowed with two 4,6-diphenylpyrimidine ligands and two acetylacetonate ligands, with one of the former being the rigid bridging unit between the two metal centers. The heterodinuclear complex exhibits red phosphorescence with a high quantum yield of Phi(PL) = 85% and a short room-temperature decay time of tau = 640 ns in degassed toluene solution. The high efficiency of the spin-forbidden T-1 -> S-0 transition is demonstrated to originate in a strong spin-orbit coupling of the T-1 state with a manifold of excited singlet states, which contributes to the record-breaking zero-field splitting of the T-1 state of 240 cm(-1). The high-solubility and non-ionic hetero-dinuclear complex was employed as the emissive guest compound in host-guest light-emitting electrochemical cells, and such optimized devices delivered vibrant red emission (lambda(peak) = 615 nm) with a second-fast turn-on and a high external quantum efficiency of 2.7% at a luminance of 265 cd m(-2).

  • 84.
    Sharifi, Tiva
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Larsen, Christian
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wang, Jia
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Kwong, Wai Ling
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Gracia-Espino, Eduardo
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Mercier, Guillaume
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Messinger, Johannes
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Toward a Low-Cost Artificial Leaf: Driving Carbon-Based and Bifunctional Catalyst Electrodes with Solution-Processed Perovskite Photovoltaics2016In: Advanced Energy Materials, ISSN 1614-6832, Vol. 6, no 20, p. 1-10, article id 1600738Article in journal (Refereed)
    Abstract [en]

    Molecular hydrogen can be generated renewably by water splitting with an artificial-leaf device, which essentially comprises two electrocatalyst electrodes immersed in water and powered by photovoltaics. Ideally, this device should operate efficiently and be fabricated with cost-efficient means using earth-abundant materials. Here, a lightweight electrocatalyst electrode, comprising large surface-area NiCo2O4 nanorods that are firmly anchored onto a carbon-paper current collector via a dense network of nitrogen-doped carbon nanotubes is presented. This electrocatalyst electrode is bifunctional in that it can efficiently operate as both anode and cathode in the same alkaline solution, as quantified by a delivered current density of 10 mA cm(-2) at an overpotential of 400 mV for each of the oxygen and hydrogen evolution reactions. By driving two such identical electrodes with a solution-processed thin-film perovskite photovoltaic assembly, a wired artificial-leaf device is obtained that features a Faradaic H-2 evolution efficiency of 100%, and a solar-to-hydrogen conversion efficiency of 6.2%. A detailed cost analysis is presented, which implies that the material-payback time of this device is of the order of 100 days.

  • 85.
    Shin, Joon Ho
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Matyba, Piotr
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Robinson, Nathaniel D.
    Department of Science and Technology, Linköpings Universitet, SE-601 74 Norrköping, Sweden.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    The influence of electrodes on the performance of light-emitting electrochemical cells2007In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 52, no 23, p. 6456–6462-Article in journal (Refereed)
    Abstract [en]

    We demonstrate that the electrochemical properties of the electrode material can have a dramatic impact on the performance of light-emitting electrochemical cells (LECs). Specifically, we report results from planar wide-gap LECs containing a blend of poly(2-methoxy,5-(2’-ethylhexyloxy)-p-phenylene vinylene) (MEH-PPV), poly(ethylene oxide) and LiCF3SO3 as the active material. We find that Au electrodes are preferable over Al electrodes, since Au-electrode devices exhibit fast turn-on (i.e., p-n junction formation time) and clearly visible light emission during operation at 5 V and 360 K, while Al-electrode devices exhibit slow turn-on (due to a delayed onset of p-doping progression) and no visible light emission. These results are rationalized with a cyclic voltammetry study, which demonstrates that Al is oxidized at a lower potential than the p-doping (oxidation) potential of MEH-PPV, while Au is electrochemically inert over the entire voltage range spanned by the p- and n-doping potentials of MEH-PPV. Consequently, the oxidation charge injected into Al-electrode devices results in a combination of p-doping of MEH-PPV and formation of Al ions. The latter process is undesired since it results in a slow turn-on time and quenched light emission. Finally, we find that planar LECs in a bottom-electrode configuration exhibit a faster turn-on time than identical devices with the electrodes on top of the active material.

  • 86. Shin, Joon Ho
    et al.
    Robinson, Nathaniel D.
    Xiao, Steven
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Physics.
    Polymer Light-Emitting Electrochemical Cells: Doping Concentration, Emission Zone Position, and Turn-on Time.2007In: Advanced Functional Materials, Vol. 17, p. 1807-1813Article in journal (Refereed)
    Abstract [en]

    By direct optical probing of the doping progression and simultaneous recording of the current-time behavior, we are able to establish the position of the light-emitting p-n junction, the doping concentrations in the p- and n-type regions, and the turn-on time for a number of planar light-emitting electrochemical cells (LECs) with a 1 mm interelectrode gap. We find that the position of the p-n junction in such LECs with Au electrodes contacting an active material mixture of poly(2-methoxy,5-(2’-ethylhexyloxy)-p-phenylene vinylene) (MEH-PPV), poly(ethylene oxide), and a XCF3SO3 salt (X = Li, K, Rb) is dependent on the salt selection: for X = Li the p-n junction is positioned very close to the negative electrode, while for X = K, Rb it is significantly more centered in the interelectrode gap. We demonstrate that this results from that the p-type doping concentration is independent on salt selection at ~21020 cm-3 (~0.1 dopants/MEH-PPV repeat unit), while the n-type doping concentration exhibits a strong dependence: for X = K it is ~51020 cm-3 (~0.2 dopants/repeat unit), for X = Rb it is ~91020 cm-3 (~0.4 dopants/repeat unit), and for X = Li it is ~31021 /cm-3 (~1 dopants/repeat unit). Finally, we demonstrate that X = K, Rb devices exhibit significantly faster turn-on times than X = Li devices, which is a consequence of a higher ionic conductivity in the former devices.

  • 87.
    Shin, Joon-Ho
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Dzwilewski, Andrzej
    Umeå University, Faculty of Science and Technology, Physics.
    Iwasiewicz, Agnieszka
    Umeå University, Faculty of Science and Technology, Physics.
    Xiao, Steven
    Fransson, Åke
    Applied Physics and Electronics.
    Ankah, Genesis Ngwa
    Umeå University, Faculty of Science and Technology, Physics.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Physics.
    Light emission at 5 V from a polymer device with a millimeter-sized interelectrode gap2006In: Applied Physics Letters, Vol. 89, p. 013509-Article in journal (Refereed)
  • 88.
    Shin, Joon-Ho
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Physics.
    Light-Emitting Electrochemical Cells with Millimeter-Sized Interelectrode Gap: Low-Voltage Operation at Room Temperature2006In: Journal of the American Chemical Society, Vol. 128, p. 15568-15569Article in journal (Refereed)
  • 89.
    Shin, Joon-Ho
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Xiao, S.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Physics.
    Polymer Light-Emitting Electrochemical Cells: The Formation and Effects of Doping-Induced Micro Shorts2006In: Advanced Functional Materials, Vol. 16, p. 949-56Article in journal (Refereed)
  • 90.
    Shin, Joon-Ho
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Xiao, Steven
    Fransson, Åke
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Polymer light-emitting electrochemical cells: frozen-junction operation of an “ionic liquid” device2005In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 87, no 4, article id 043506Article in journal (Refereed)
    Abstract [en]

    We report frozen-junction operation of a polymer light-emitting electrochemical cell containing a mixture of poly[2-methoxy-5-(2(')-ethyl-hexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and the ionic liquid tetra-n-butylammonium trifluoromethanesulfonate (TBA-TF) as the active material. We find fast turn-on time, unipolar light emission, and significant operational lifetime up to T=200 K for planar Au/(TBA-TF+MEH-PPV)/Au surface cells, which had been charged (i.e., electrochemically p- and n-type doped in situ) at T=393 K and V=4 V and then cooled to 80 K at V=4 V. We employed differential scanning calorimetry to demonstrate that (TBA-TF+MEH-PPV) exhibits two melting transitions of TBA-TF crystalline phases located at T(m,1)approximate to 280 K and T(m,2)approximate to 380 K, respectively. The lower T-m,T-1 sets the upper limit for frozen-junction operation (with zero-ionic conductivity), while the larger T-m,T-2 correlates to the lower limit for the charging regime (with high ionic conductivity).

  • 91. Summers, Melissa A.
    et al.
    Burrato, Steven K.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Physics.
    Morphology and Environment-Dependent Fluorescence in Blends Containing a Phenylenevinylene Conjugated Polymer.2007In: Thin Solid Films, Vol. 515, p. 8412-8418Article in journal (Refereed)
    Abstract [en]

    Near-field scanning optical microscopy and single molecule spectroscopy have been employed to study a large number of blends containing a highly fluorescent and amorphous conjugated polymer, ‘superyellow’ (a phenylenevinylene copolymer). We find that blend films with a non-fluorescent and semi-crystalline polymer, poly(ethylene oxide) (PEO), with a superyellow content between 9 and 50 mass% exhibit phase separation with no evidence for admixing of the two components, while films with a lower superyellow content of ≤ 1 mass% content comprise a solid-state solution of superyellow within a crystalline PEO matrix. Interestingly, films with approximately the same amount of superyellow as PEO (similar to those used in, e.g., light-emitting electrochemical cells) exhibit a bi-continuous network morphology. We also report that the superyellow fluorescence spectrum shows a remarkable sensitivity to the physical and chemical environment of superyellow.

  • 92. Summers, Melissa A.
    et al.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Physics.
    Burrato, Steven K.
    Heeger, Alan J.
    Morphology-Dependent Luminescence in Blends of a Phenylenevinylene-Based Polymer and Polyethylene Oxide.2005In: Extended Abstracts – 2005 Materials Research Society Fall Meeting, 2005Conference paper (Other academic)
  • 93. Summers, Melissa A.
    et al.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Physics.
    Swenson, James
    Heeger, Alan J.
    Burrato, Steven K.
    Applications of Near-Field Scanning Optical Microscopy to Organic Light-Emitting Electrochemical Cell Materials and Devices.2004In: Extended Abstracts – American Chemical Society Spring meeting, 2004Conference paper (Other academic)
  • 94.
    Tang, Shi
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. LunaLEC AB, Umeå.
    Buchholz, Herwig A.
    Merck KGaA, Darmstadt, Germany .
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    On the selection of a host compound for efficient host-guest light-emitting electrochemical cells2015In: Journal of Materials Chemistry C, ISSN 2050-7526, E-ISSN 2050-7534, Vol. 3, no 31, p. 8114-8120Article in journal (Refereed)
    Abstract [en]

    A light-emitting electrochemical cell (LEC) is characterized by its electrochemical doping operation that facilitates advantages as regards device fabrication and functionality, but it currently suffers from the drawback that the efficiency at significant luminance is not very high. A viable solution to this setback could be the implementation of a host-guest active material, where the majority host transports the electronic charge and the guest is a triplet emitter that features an appropriate energy structure for facile exciton transfer and trapping as well as for efficient light emission. Here, we demonstrate that an additional critical property of a functional host-guest LEC is that the host can be electrochemically p- and n-type doped, as can be deduced from screening studies on open planar devices and by cyclic voltammetry. LEC devices based on hosts that do not fulfill this fundamental criterion are shown to suffer from low luminance and poor efficiency, whereas host-guest LECs, based on a host material capable of electrochemical doping, exhibit a much improved luminance and efficiency, with the efficiency being well retained at high luminance values also.

  • 95.
    Tang, Shi
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. LunaLEC AB, Umeå, Sweden.
    Buchholz, Herwig A
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics. LunaLEC AB, Umeå, Sweden.
    White Light from a Light-Emitting Electrochemical Cell: Controlling the Energy-Transfer in a Conjugated Polymer/Triplet-Emitter Blend2015In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 7, no 46, p. 25955-25960Article in journal (Refereed)
    Abstract [en]

    We report on the attainment of broadband white light emission from a hostguest light-emitting electrochemical cell, comprising a blue-emitting conjugated polymer as the majority host and a red-emitting small-molecule triplet emitter as the minority guest. An analysis of the energy structure reveals that host-to-guest energy transfer can be effectuated by both Forster and Dexter processes, and through a careful optimization of the active material composition partial energy transfer and white emission is accomplished at a low guest concentration of 0.5%. By adding a small amount of a yellow-emitting conjugated polymer to the active material, white light emission with a high color rendering index of 79, and an efficiency of 4.3 cd/A at significant luminance (>200 cd/m2), is realized.

  • 96.
    Tang, Shi
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. LunaLEC, Umeå, Sweden.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics. LunaLEC, Umeå, Sweden.
    Light-Emitting Electrochemical Cells: A Review on Recent Progress2016In: Topics in Current Chemistry, ISSN 2365-0869, Vol. 374, no 4, article id 40Article, review/survey (Refereed)
    Abstract [en]

    The light-emitting electrochemical cell (LEC) is an area-emitting device, which features a complex turn-on process that ends with the formation of a p-n junction doping structure within the active material. This in-situ doping transformation is attractive in that it promises to pave the way for an unprecedented low-cost fabrication of thin and light-weight devices that present efficient light emission at low applied voltage. In this review, we present recent insights regarding the operational mechanism, breakthroughs in the development of scalable and adaptable solution-based methods for cost-efficient fabrication, and successful efforts toward the realization of LEC devices with improved efficiency and stability.

  • 97.
    Tang, Shi
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Quest for an Appropriate Electrolyte for High-Performance Light-Emitting Electrochemical Cells2010In: Journal of physical chemistry letters, Vol. 1, no 18, p. 2727-2732Article in journal (Refereed)
    Abstract [en]

    The electrolyte plays a critical role in the operation of light-emitting electrochemical cells (LECs), and the LEC operational stability and efficiency can be severely limited by electrolyte-induced side reactions. Here we employ a trimethylolpropane-LiCF3SO3 electrolyte with a particularly wide electrochemical stability window and for-the-purpose appropriate transport properties to minimize cathodic side reactions and to keep the emission zone free from electrolyte species during steady-state operation. We utilize an optimized blend of this electrolyte and the conjugated polymer superyellow as the active material sandwiched between air-stable electrodes, and we demonstrate that such LEC devices can exhibit a notably respectable operational lifetime (57 days of uninterrupted operation at a brightness of >100 cd/m2) and a high efficiency (>10 lm/W at >100 cd/m2).

  • 98.
    Tang, Shi
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Irgum, Knut
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Chemical stabilization of doping in conjugated polymers2010In: Organic electronics, ISSN 1566-1199, E-ISSN 1878-5530, Vol. 11, no 6, p. 1079-1087Article in journal (Refereed)
    Abstract [en]

    Conjugated polymers can be electrochemically doped to high-conductivity states under applied voltage, but such in situ formed doping structures are dynamic and dissipate when the formation voltage is removed. For some applications it is highly desirable to permanently stabilize the doping after its formation. Here, we report and compare results on four different approaches to chemical stabilization of an emissive and rectifying p–n junction doping structure in a light-emitting electrochemical cell (LEC) application: (i) polymerization of the dopant counter-ions, (ii) polymerization of the counter-ions utilizing a radical-initiator compound, (iii) polymerization of the ion-transport material, and (iv) polymerization of both the counter-ions and the ion-transport material utilizing a radical-initiator compound. We found that approach (i) resulted in LEC devices with poor stability, current rectification and light-emission, and that approach (ii) solely yielded a notable improvement in the light-emission. Approach (iii) resulted in good current rectification and stability, but the overall best results were clearly attained with approach (iv) as such stabilized LEC devices exhibited a respectable current rectification ratio of 2000, as well as a decent light-emission efficiency and long-term stability under idle conditions.

  • 99.
    Tang, Shi
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Mindemark, Jonas
    Department of Chemistry − Ångström Laboratory, Uppsala University, Uppsala, Sweden.
    Araujo, Carlos Moyses Graca
    Materials Theory Division, Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Brandell, Daniel
    Department of Chemistry − Ångström Laboratory, Uppsala University, Uppsala, Sweden.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics. ludvig.edman@physics.umu.se.
    Identifying Key Properties of Electrolytes for Light-Emitting Electrochemical Cells2014In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 26, no 17, p. 5083-5088Article in journal (Refereed)
    Abstract [en]

    The electrolyte is a key component in light-emitting electrochemical cells (LECs), as it facilitates in situ electrochemical doping and associated attractive device features. LiCF3SO3 dissolved in hydroxyl-capped trimethylolpropane ethoxylate (TMPE-OH) constitutes an electrolyte with which we have attained high stability and efficiency for polymer LECs, but the turn-on time of such devices is unfortunately slow. By replacing hydroxyl with methoxy as the TMPE end-group, we produced LECs with a desired combination of high efficiency, good stability, and fast turn-on time. Specifically, we showed that the turn-on time to high luminance (300 cd/m(2)) at a current density of 7.7 mA/cm(2) is lowered from 1740 to 16 s, that the efficiency is improved by similar to 20%, and that the other device properties are either maintained or improved. In a parallel modeling and experimental effort, we demonstrated that the faster kinetics following the shift in the TMPE end-group is attributed to a marked decrease in the level of both inter- and intramolecular interactions of the electrolyte, as manifested in a lowered electrolyte viscosity, faster ion transport, and more facile ion release during doping.

  • 100.
    Tang, Shi
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. LunaLEC AB.
    Murto, Petri
    Wang, Jia
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Larsen, Christian
    Umeå University, Faculty of Science and Technology, Department of Physics. LunaLEC AB.
    Andersson, Mats R.
    Wang, Ergang
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics. LunaLEC AB.
    On the Design of Host-Guest Light-Emitting Electrochemical Cells: Should the Guest be Physically Blended or Chemically Incorporated into the Host for Efficient Emission?2019In: Advanced Optical Materials, ISSN 2162-7568, E-ISSN 2195-1071, Vol. 7, no 18, article id 1900451Article in journal (Refereed)
    Abstract [en]

    It has recently been demonstrated that light‐emitting electrochemical cells (LECs) can be designed to deliver strong emission with high efficiency when the charge transport is effectuated by a majority host and the emission is executed by a minority guest. A relevant question is then: should the guest be physically blended with or chemically incorporated into the host? A systematic study is presented that establishes that for near‐infrared‐(NIR‐) emitting LECs based on poly(indacenodithieno[3,2‐b]thiophene) (PIDTT) as the host and 4,7‐bis(4,4‐bis(2‐ethylhexyl)‐4H‐silolo[3,2‐b:4,5‐b′]dithiophen‐2‐yl)benzo[c][1,2,5]‐thiadiazole (SBS) as the guest the chemical‐incorporation approach is preferable. The host‐to‐guest energy transfer in LEC devices is highly efficient at a low guest concentration of 0.5%, whereas guest aggregation and ion redistribution during device operation severly inhibits this transfer in the physical‐blend devices. The chemical‐incorporation approach also results in a redshifted emission with a somewhat lowered photoluminescence quantum yield, but the LEC performance is nevertheless very good. Specifically, an NIR‐LEC device comprising a guest‐dilute (0.5 molar%) PIDTT‐SBS copolymer delivers highly stabile operation at a high radiance of 263 µW cm−2 (peak wavelength = 725 nm) and with an external quantum efficiency of 0.214%, which is close to the theoretical limit for this particular emitter and device geometry.

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