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Functional and Flexible Light-Emitting Electrochemical Cells
Umeå University, Faculty of Science and Technology, Department of Physics. (Institutionen för fysik, Department of Physics)ORCID iD: 0000-0003-3759-6381
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The introduction of artificial illumination has brought extensive benefits to mankind, and during the last years we have seen a tremendous progress in this field with the introduction of the energy-efficient light-emitting diode (LED) and the high-contrast organic LED display. These high-end technologies are, however, produced using costly and complex processes, and it is anticipated that the next big thing in the field will be the advent of a low-cost and “green” illumination technology, which can be fabricated in a cost- and material-efficient manner using non-toxic and abundant raw materials, and which features attractive form factors such as flexibility, robustness and light-weight. The light-emitting electrochemical cell (LEC) is a newly invented illumination technology, and in this thesis we present results that imply that it can turn the above vision into reality.

The thin-film LEC comprises an active material sandwiched between a cathode and an anode as its key constituent parts. With the aid of a handheld air-brush, we show that functional large-area LECs can be fabricated by simply spraying three layers of solution -- forming the anode, active material, and cathode -- on top of a substrate. We also demonstrate that such “spray-sintered” LECs can feature multicolored emission patterns, and be fabricated directly on complex-shaped surfaces, with one notable example being the realization of a light-emission fork!

Almost all LECs up-to-date have been fabricated on glass substrates, but for a flexible and light-weight emissive device, it is obviously relevant to identify more appropriate substrate materials. For this end, we show that it is possible to spray-coat the entire LEC directly on conventional copy paper, and that such paper-LECs feature uniform light-emission even under heavy bending and flexing.

We have further looked into the fundamental aspects of the LEC operation and demonstrated that the in-situ doping formation, which is a characteristic and heralded feature of LECs, can bring problems in the form of doping-induced self-absorption. By quantitatively analyzing this phenomenon, we provided straightforward guidelines on how future efficiency-optimized LEC devices should be designed.

The in-situ doping formation process brings the important advantage that LECs can be fabricated from solely air-stabile materials, but during light emission the device needs to be protected from the ambient air. We have therefore developed a functional glass/epoxy encapsulation procedure for the attainment of LEC devices that feature a record-long ambient-air operational lifetime of 5600 h. For the light-emission device of the future, it is however critical that the encapsulation is flexible, and in our last study, we show that the use of multi-layer barrier can result in high-performance flexible LECs.

Place, publisher, year, edition, pages
Umeå: Umeå University , 2015. , 57 p.
Keyword [en]
all-ambient fabrication, ambient-air lifetime, encapsulation, flexible, light-emitting electrochemical cells, light-emitting paper
National Category
Nano Technology Other Physics Topics
Research subject
Physics
Identifiers
URN: urn:nbn:se:umu:diva-102400ISBN: 978-91-7601-257-4 (print)OAI: oai:DiVA.org:umu-102400DiVA: diva2:807559
Public defence
2015-05-22, N300, Naturvetarhuset, Umeå University, Umeå, 10:00 (English)
Opponent
Supervisors
Available from: 2015-04-30 Created: 2015-04-23 Last updated: 2015-05-08Bibliographically approved
List of papers
1. Light-Emitting Paper
Open this publication in new window or tab >>Light-Emitting Paper
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2015 (English)In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 25, no 21, 3238-3245 p.Article in journal (Refereed) Published
Abstract [en]

A solution-based fabrication of flexible and light-weight light-emitting devices on paper substrates is reported. Two different types of paper substrates are coated with a surface-emitting light-emitting electrochemical cell (LEC) device: a multilayer-coated specialty paper with an intermediate surface roughness of 0.4 μm and a low-end and low-cost copy paper with a large surface roughness of 5 μm. The entire device fabrication is executed using a handheld airbrush, and it is notable that all of the constituent layers are deposited from solution under ambient air. The top-emitting paper-LECs are highly flexible, and display a uniform light emission with a luminance of 200 cd m−2 at a current conversion efficacy of 1.4 cd A−1.

Keyword
Ag nanowires, all-ambient fabrication, light-emitting electrochemical cells, paper substrates, spray coating
National Category
Other Physics Topics Nano Technology
Identifiers
urn:nbn:se:umu:diva-101921 (URN)10.1002/adfm.201500528 (DOI)000355635300015 ()
Available from: 2015-04-15 Created: 2015-04-15 Last updated: 2017-12-04Bibliographically approved
2. Spraying Light: Ambient-Air Fabrication of Large-Area Emissive Devices on Complex-Shaped Surfaces
Open this publication in new window or tab >>Spraying Light: Ambient-Air Fabrication of Large-Area Emissive Devices on Complex-Shaped Surfaces
2014 (English)In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 26, no 29, 4975-4980 p.Article in journal (Refereed) Published
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.

Keyword
large-area light emission, complex surfaces, solution-based processing, ambient fabrication, light-emitting electrochemical cell
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:umu:diva-93224 (URN)10.1002/adma.201401286 (DOI)000340500700011 ()
Available from: 2014-12-22 Created: 2014-09-15 Last updated: 2017-12-05Bibliographically approved
3. Encapsulating light-emitting electrochemical cells for improved performance
Open this publication in new window or tab >>Encapsulating light-emitting electrochemical cells for improved performance
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2012 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 100, 193508Article in journal (Refereed) Published
Abstract [en]

We present a functional and scalable encapsulation of light-emitting electrochemical cells (LECs), which results in a measured ambient operation of >400 h at a brightness of >300 cd/m(2) with a maximum efficacy of 6 lm/W, and a linearly extrapolated ambient operation of similar to 5600 h at >100 cd/m(2). Our findings suggest that previous studies have underestimated the practical stability of appropriately encapsulated LECs. We also report that the dominant ambient degradation for non-encapsulated LECs is water-induced delamination of the cathode from the active layer, while encapsulated LECs in contrast are found to decay from spatial variations in the active layer composition. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4714696]

National Category
Physical Sciences
Identifiers
urn:nbn:se:umu:diva-56420 (URN)10.1063/1.4714696 (DOI)000304108000097 ()
Available from: 2012-06-19 Created: 2012-06-18 Last updated: 2017-12-07Bibliographically approved
4. A Flexible Encapsulation Structure for Ambient-Air Operation of Light-Emitting Electrochemical Cells
Open this publication in new window or tab >>A Flexible Encapsulation Structure for Ambient-Air Operation of Light-Emitting Electrochemical Cells
2016 (English)In: Advanced Engineering Materials, ISSN 1438-1656, E-ISSN 1527-2648, Vol. 18, no 1, 105-110 p.Article in journal (Other academic) Published
Abstract [en]

The emerging field of organic electronics is heralded because it promises low-cost and flexible devices, and it was recently demonstrated that a light-emitting electrochemical cell (LEC) can be fabricated with cost-efficient methods under ambient air. However, the LEC turns sensitive to oxygen and water during light-emission, and it is therefore timely to identify flexible encapsulation structures. Here, we demonstrate that a multilayer film, featuring a water and oxygen barrier property of ≈1 × 10–3 g/m2/day and ≈1 × 10–3 cm3/m2/bar/day respectively, is fit for this task. By sandwiching an LEC between such multilayer barriers, as attached by a UV-curable epoxy, we realize flexible LECs with performance on par with identical glass-encapsulated devices, and which remain functional after one year storage under air.

National Category
Nano Technology
Research subject
Physics
Identifiers
urn:nbn:se:umu:diva-102398 (URN)10.1002/adem.201500245 (DOI)000370146000014 ()
Note

Originally included in thesis in manuscript form.

Available from: 2015-04-23 Created: 2015-04-23 Last updated: 2017-12-04Bibliographically approved
5. Doping-Induced Self-Absorption in Light-Emitting Electrochemical Cells
Open this publication in new window or tab >>Doping-Induced Self-Absorption in Light-Emitting Electrochemical Cells
2014 (English)In: ACS PHOTONICS, ISSN 2330-4022, Vol. 1, no 3, 182-189 p.Article in journal (Refereed) Published
Abstract [en]

We report on the quantitative effects of doping-induced self-absorption in light-emitting electrochemical cells (LECs) as a function of active material (AM) thickness and doping concentration. For state-of-the-art polymer LECs with optimized doping concentration and comprising Super Yellow as the electroluminescent (EL) polymer and poly(ethylene oxide)-KCF3SO3 as the electrolyte, we find that the self-absorption loss at the EL peak wavelength is similar to 10% for a 100 nm thin AM and >70% for a 1 mu m thick AM. This implies that the utilization of micrometer-thick AMs fit for fault-tolerant large-scale fabrication can be concomitant with a notable penalty in device performance, and that spatial variations in AM thickness will be manifested in a corresponding spatial light-intensity variation. Moreover, we find that inclusion of a poly(ethylene oxide)-KCF3SO3 electrolyte can inhibit the out-coupling of light and suggest that the culprit is light scattering from dispersed crystalline-electrolyte domains. Finally, we demonstrate evidence for that the selected initial salt concentration in an LEC device dictates the maximum doping concentration that can be attained at steady-state operation.

Keyword
light-emitting device, organic electronics, electroluminescence, electrochemical doping, cyclic voltammetry, conjugated polymer
National Category
Physical Sciences
Identifiers
urn:nbn:se:umu:diva-90793 (URN)10.1021/ph400050t (DOI)000335802900006 ()
Available from: 2014-10-09 Created: 2014-07-01 Last updated: 2015-04-24Bibliographically approved

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