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Bilayer Light-Emitting Electrochemical Cells for Signage and Lighting Applications
Umeå University, Faculty of Science and Technology, Department of Physics. (The Organic Photonics and Electronics Group)ORCID iD: 0000-0002-1903-9875
2016 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Artificial light surrounds us in a manifold of shapes. It is mainly utilized for illumination, but also for graphical communication of complex and evolving messages and information, among other things. It can be generated in different ways with incandescent lamps and fluorescent tubes constituting two common examples. Organic solid state light-generation technologies, which boast advantages such as solution processability, thin and flexible form factors, and large versatility, are modern additions to the field. But regardless of the means of generation, whenever light is to be used to communicate information, as signage or displays, it needs to be patterned. Unfortunately patterning is often complicated and expensive from a fabrication point of view, or renders the devices inefficient. To bridge the gap between present technologies and the need for low-cost and low-complexity patterned light emitters, it is important to develop new device architectures and/or fabrication procedures.

In this thesis we show that patterned light emission can be attained from solution processable bilayer light-emitting electrochemical cells (LECs), in which the bilayer stack comprises an electrolyte and an organic semiconductor as the first and second layer, respectively. We investigate a subtractive direct-write approach, in which electrolyte is displaced and patterned by the contact motion of a thin stylus, as well as an additive inkjet-patterning technique. Both result in electroluminescent patterns, e.g., light-emitting sketches and microscopic signage with high pixel density. But they can also build macroscopic patterned regions with homogeneous emission depending on the design of electrolyte features. Using an in-operando optical microscopy study we have investigated the operational physics and some limiting factors of the bilayer LECs. More specifically we find that the electrolyte film homogeneity is a key property for high optical quality, and that the emitting region is defined by the location of the interfaces between electrolyte, anode, and organic semiconductor. We observe that the cationic diffusion length is less than one micrometer in our employed organic semiconductors, and rationalize the localized emission by cationic electric double-layer formation at the cathode, and the electronically insulating electrolyte at the anode.

To date, the presented luminescent signage devices feature high-resolution patterns, in both pixelated and line-art form, and show great robustness in terms of fabrication and material compatibility. Being LECs, they have the potential for truly low-cost solution processing, which opens up for new applications and implementations. However, these first reports on patterned bilayer LECs leave plenty of room for improvements of the optical and electronic characteristics. For instance, if the optoelectronic properties of the devices were better understood, a rational design of microscopic electrolyte features could provide for both more efficient LECs, and for more homogeneous light emission from the patterned regions.

Place, publisher, year, edition, pages
Umeå: Umeå universitet , 2016. , 30 p.
Keyword [en]
Organic electronics, Light-emitting electrochemical cell, Signage, Display, Luminescent line art, Inkjet printing, Direct-write printing
National Category
Atom and Molecular Physics and Optics Condensed Matter Physics
Research subject
Physics; Electronics
Identifiers
URN: urn:nbn:se:umu:diva-114500ISBN: 978-91-7601-390-8 (print)OAI: oai:DiVA.org:umu-114500DiVA: diva2:896406
Presentation
2016-02-19, N430, Naturvetarhuset, Umeå, 09:00 (English)
Supervisors
Funder
ÅForsk (Ångpanneföreningen's Foundation for Research and Development)Swedish Foundation for Strategic Research Swedish Energy AgencyKnut and Alice Wallenberg FoundationThe Kempe Foundations
Available from: 2016-01-22 Created: 2016-01-21 Last updated: 2016-01-22Bibliographically approved
List of papers
1. Inkjet Printed Bilayer Light-Emitting Electrochemical Cells for Display and Lighting Applications
Open this publication in new window or tab >>Inkjet Printed Bilayer Light-Emitting Electrochemical Cells for Display and Lighting Applications
2014 (English)In: Small, ISSN 1613-6810, E-ISSN 1613-6829, Vol. 10, no 20, 4148-4153 p.Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
John Wiley & Sons, 2014
Keyword
inkjet printing, light-emitting electrochemical cells, displays, patterning, conjugated polymers
National Category
Physical Sciences
Identifiers
urn:nbn:se:umu:diva-96951 (URN)10.1002/smll.201400840 (DOI)000344452500015 ()
Available from: 2015-02-25 Created: 2014-12-05 Last updated: 2017-12-04Bibliographically approved
2. Luminescent line art by direct-write patterning
Open this publication in new window or tab >>Luminescent line art by direct-write patterning
2016 (English)In: Light: Science & Applications, ISSN 2047-7538, Vol. 5, e16050Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Nature Publishing Group, 2016
Keyword
direct-write patterning, light-emitting electrochemical cell, luminescent line art, organic electronics
National Category
Other Physics Topics
Research subject
Physics
Identifiers
urn:nbn:se:umu:diva-114168 (URN)10.1038/lsa.2016.50 (DOI)000374463100006 ()
Funder
Knut and Alice Wallenberg FoundationThe Kempe FoundationsÅForsk (Ångpanneföreningen's Foundation for Research and Development)Swedish Energy AgencySwedish Research CouncilSwedish Foundation for Strategic Research
Available from: 2016-01-15 Created: 2016-01-15 Last updated: 2016-06-17Bibliographically approved

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