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A Flexible Encapsulation Structure for Ambient-Air Operation of Light-Emitting Electrochemical Cells
Umeå University, Faculty of Science and Technology, Department of Physics.
Umeå University, Faculty of Science and Technology, Department of Physics.
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.

Place, publisher, year, edition, pages
2016. Vol. 18, no 1, 105-110 p.
National Category
Nano Technology
Research subject
Physics
Identifiers
URN: urn:nbn:se:umu:diva-102398DOI: 10.1002/adem.201500245ISI: 000370146000014OAI: oai:DiVA.org:umu-102398DiVA: diva2:807534
Note

Originally included in thesis in manuscript form.

Available from: 2015-04-23 Created: 2015-04-23 Last updated: 2017-12-04Bibliographically approved
In thesis
1. Functional and Flexible Light-Emitting Electrochemical Cells
Open this publication in new window or tab >>Functional and Flexible Light-Emitting Electrochemical Cells
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
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:nbn:se:umu:diva-102400 (URN)978-91-7601-257-4 (ISBN)
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

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