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Luminescent line art by direct-write patterning
Umeå University, Faculty of Science and Technology, Department of Physics. (The Organic Photonics and Electronics Group)ORCID iD: 0000-0002-1903-9875
Umeå University, Faculty of Science and Technology, Department of Physics. LunaLEC AB, Umeå, Sweden . (The Organic Photonics and Electronics Group)
University of South Australia.
Umeå University, Faculty of Science and Technology, Department of Physics. LunaLEC AB, Umeå, Sweden . (The Organic Photonics and Electronics Group)ORCID iD: 0000-0003-2495-7037
2016 (English)In: Light: Science & Applications, ISSN 2047-7538, Vol. 5, article id 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. Vol. 5, article id e16050
Keywords [en]
direct-write patterning, light-emitting electrochemical cell, luminescent line art, organic electronics
National Category
Other Physics Topics
Research subject
Physics
Identifiers
URN: urn:nbn:se:umu:diva-114168DOI: 10.1038/lsa.2016.50ISI: 000374463100006OAI: oai:DiVA.org:umu-114168DiVA, id: diva2:894664
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: 2019-02-05Bibliographically approved
In thesis
1. Bilayer Light-Emitting Electrochemical Cells for Signage and Lighting Applications
Open this publication in new window or tab >>Bilayer Light-Emitting Electrochemical Cells for Signage and Lighting Applications
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. p. 30
Keywords
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:nbn:se:umu:diva-114500 (URN)978-91-7601-390-8 (ISBN)
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: 2018-06-07Bibliographically approved
2. On the operation of light-emitting electrochemical cells
Open this publication in new window or tab >>On the operation of light-emitting electrochemical cells
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

We are in the midst of a technological revolution that permeates nearly all human activities; artificial light is one of the most visible contributors in this societal change. If more efficient, green, and versatile light sources can be developed, they might improve the life of millions of people around the world while causing minimal damage to our climate and environment. The unique operational mechanism of the light-emitting electrochemical cell (LEC) makes it an ideal fit for some unconventional and emerging uses of light, in for example medicine and security.

By exploiting this operational mechanism, in which mobile ions enable electrochemical doping of a luminescent polymer, we have designed and fabricated new bilayer LEC architectures. The bilayer LEC features patterned light emission that is easily adjustable during fabrication, and that can be configured to suit new applications of light. Given the light-emitting nature of the LEC, it is somewhat surprising that the optical understanding of its operation is rather limited. To fill this knowledge gap, we investigate how the optical properties of the luminescent polymer respond to electrochemical doping. We find that the complex-refractive index spectrum in the active layer of an LEC, as a direct result of the doping, varies in both space and time. The thin-film structure of an LEC implies that computational predictions of its luminous output need to consider internal reflections and interference. Finally, we implement a doping dependent optical thin-film simulation model. It enables us to precisely replicate the experimental luminance and angle-dependent emission spectrum for a range of LECs with different thicknesses. Using the model we can also identify and quantify many of the different optical loss mechanisms in LECs, which has not previously been done. The insights that we have collected on the path towards our present model will be useful for computational determination of device parameters that are otherwise difficult to acquire.

The improved understanding of the optical operation of LECs is important for the maturation of the technology, as it facilitates formulation of relevant and accurate research questions. Hopefully, our results will accelerate the development of the field, so that useful products based on this technology can become available in the not too distant future.

Abstract [sv]

Just nu pågår en teknologisk revolution som genomsyrar nära nog alla samhällsfunktioner, och där artificiellt ljus har en påfallande viktig roll. Nya ljuskällor, som är mer miljövänliga, effektiva och mångsidiga, skulle kunna förbättra livskvaliten för miljoner människor över hela världen, utan att för den skull skapa problem för vår miljö och vårt klimat. Den ljusemitterande elektrokemiska cellen (LEC) är en teknik som fungerar på ett unikt sätt. Det gör att den är lämplig för nya och okonventionella användningsområden av ljus, exempelvis inom medicin och säkerhetsprodukter.

Vi har kunnat designa och tillverka en ny sorts dubbellagers-LEC genom att utnyttja den interna funktionen i en LEC. Den innebär att rörliga joner möjliggör elektrokemiska oxidations- och reduktionsprocesser (dopning) av en lysande polymer. En dubbellagers-LEC lyser i mönster som enkelt kan anpassas utefter önskemål, och skulle kunna användas i nya sorters ljusapplikationer. Med tanke på att en LEC är en lysande komponent är förståelsen för dess optik förvånansvärt begränsad. För att förbättra dessa kunskaper börjar vi med att undersöka hur den lysande polymerens optiska egenskaper förändras när den dopas. Vi finner att dess optiska egenskaper varierar i tid och rum i det aktiva skiktet i en LEC, som en direkt följd av dopningen. För att sedan med hjälp av de optiska egenskaperna kunna beräkna hur mängden ljus påverkas, måste vi också ta hänsyn till att ljus i tunna skikt kan reflekteras vid gränsytor och interagera med sig själv. Slutligen implementerar vi en dopningsberoende optisk beräkningsmodell för tunna skikt, och lyckas återskapa den experimentellt uppmätta luminansen och de vinkelberoende ljusspektrumen för en serie LECer med olika tjocklek. Utifrån modellen kan vi också identifiera och kvantifiera många av de olika optiska förlustkanalerna i en LEC, vilket inte gjorts tidigare. Vägen fram till den nuvarande modellen har bjudit oss på en rad insikter som gör att vi beräkningsmässigt kan uppskatta komponentegenskaper som annars skulle förbli okända, då de inte går att mäta med direkta metoder.

Den förbättrade optiska förståelsen för LEC-tekniken är viktig för forskningen inom fältet. Våra resultat kan förhoppningsvis accelerera utvecklingen mot bra och användbara produkter, så att dessa blir tillgängliga inom en inte alltför avlägsen framtid.

Place, publisher, year, edition, pages
Umeå: Umeå Universitet, 2019. p. 63
Keywords
Artificial Light, Organic Electronics, Light-emitting Electrochemical Cells, Electrochemical Doping, Thin-film Optical Model, Optical Modes
National Category
Nano Technology Other Physics Topics Condensed Matter Physics
Identifiers
urn:nbn:se:umu:diva-156093 (URN)978-91-7855-000-5 (ISBN)
Public defence
2019-03-01, Lilla hörsalen, KB.E3.01, KBC-huset, Umeå, 09:15 (English)
Opponent
Supervisors
Funder
Swedish Foundation for Strategic Research Swedish Energy AgencyÅForsk (Ångpanneföreningen's Foundation for Research and Development)Knut and Alice Wallenberg FoundationThe Kempe FoundationsSwedish Research Council
Available from: 2019-02-08 Created: 2019-02-05 Last updated: 2019-02-06Bibliographically approved

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