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Design and Fabrication of Light-Emitting Electrochemical Cells
Umeå University, Faculty of Science and Technology, Department of Physics. (Organic Photonics and Electronics)
2013 (English)Doctoral thesis, comprehensive summary (Other academic)Alternative title
Design och tillverkning av ljusemitterande elektrokemiska celler (Swedish)
Abstract [sv]

Glödlampan, en gång symbolen för mänsklig uppfinningsförmåga, är idag på väg att försvinna. Lysdioder och lågenergilampor har istället tagit över då dessa har betydligt längre livstid och högre effektivitet. Den tidigare så hyllade glödlampan anses numera vara en miljöbov, och förbud och restriktioner mot den blir allt vanligare. Trots detta så är de nya alternativen bara att betrakta som provisoriska steg på vägen mot en ideal ljuskälla, som idag tyvärr inte existerar. Lågenergilampor innehåller exempelvis kvicksilver, och utgör därmed ett direkt hot mot en användares hälsa. Både lysdioder och lågenergilampor består även av höga halter av andra tungmetaller, och är väldigt komplicerade att tillverka. Återvinning är därför ett måste, och en fullödig energibesparingsanalys måste ta hänsyn till den betydande energin som går åt vid tillverkningen. Till viss del kan detta lösas genom att göra komponenterna små och ljusstarka, men för att göra en sådan belysning angenäm används istället utrymmeskrävande och ofta energislukande lampskärmar. Lysdioder och lågenergilampor är helt enkelt bra, men långt ifrån perfekta.All elektronisk utrustning är idag beroende av metaller och inorganiska halvledare, vilket gör återvinning viktig och tillverkning komplicerad. Detta är kanske på väg att ändras då även organiska material, t.ex. plast, har visat sig kunna ha elektroniska egenskaper. Idag är organisk elektronik ett hett forskningsområde där material med liknande egenskaper som plast, fast med funktionella elektroniska egenskaper, undersöks och appliceras. Något som gör organiska material extra intressanta är att många kan lösas upp i vätskor, vilket möjliggör för skapandet av bläck. Detta leder i sin tur till möjligheter för användandet av storskaliga trycktekniker, t.ex. tidningspressar och bläckstråleskrivare, vilka leder till en stor kostnadsreduktion och förenklad tillverkning av lysande komponenter. Idag har plast redan ersatt många andra material i en mängd olika tillämpningar. Plastflaskor är vanligare än glasflaskor, och ylletröjor konkurerar idag med kläder gjorda av fleece och andra syntetiska fibrer. Med ljusemitterande plast finns det helt klart en möjlighet att en liknande utveckling kan ske även för lampor.Den här avhandlingen fokuserar på den fortsatta utvecklingen av den ljusemitterande elektrokemiska cellen (LEC), som 1995 uppfanns av Pei et al. LEC-tekniken använder sig av organiska halvledare för att konvertera elektrisk ström till ljus, men även en elektrolyt som möjliggör elektrokemisk dopning. Detta förbättrar den organiska halvledarens elektroniska egenskaper signifikant, vilket leder till mindre resistans och högre effektivitet hos den färdiga lysande komponenten.Visionen för denna och besläktade tekniker har sedan länge varit förverkligandet av en lysande tapet. Den här avhandlingen har försökt närma sig denna vision genom att visa hur en LEC kan uppnå hög effektivitet och lång livslängd, och samtidigt tillverkas i luft med storskaliga produktionsmetoder. Orsaker till en tidigare begränsad livslängd har identifierats och minimerats med hjälp av nya komponentstrukturer och materialformuleringar. En inkapslingsmetod presenteras också, vilken skyddar komponenten från syre och vatten som annars lätt reagerar med det dopade organiska materialet. Detta resulterar i en signifikant förbättring av livslängden.Genom att använda slot-die bestrykning och sprayning, båda kompatibla med rulle-till-rulle tillverkning, har möjligheter för storskalig produktion demonstrerats. Slutligen har en speciell metod för spraymålning av stora lysande ytor utvecklats.

Abstract [en]

The incandescent light bulb, once the very symbol for human ingenuity, is now being replaced by the next generation of lighting technologies such as the compact fluorescent lamp (CFL) and the light emitting diode (LED). The higher efficiencies and longer operational lifetimes of these new sources of illumination have led to the demise of the classic traditional bulb. However, it should be pointed out that the light sources that are taking over are better, but not perfect. The complex high-voltage electronic circuits and health hazardous materials required for their operation make them far from a sustainable eco-friendly option. Their fabrication is also complex, making the final product expensive. A new path forward might be through the use of plastics or other organic materials. Though not traditionally seen as electronically active, some organic materials do behave like inorganic semiconductors and substantial conductivity can be achieved by doping. Since plastics can be easily molded into complex shapes, or made into an ink using a solvent, it is expected that organic materials could revolutionize how we fabricate electronic devices in the future, and possibly replace inorganic crystals in the same way as plastics have replaced glass and wool for food storage and clothes. This thesis has focused on the light-emitting electrochemical cell (LEC), which was invented by Pei et al. in 1995. It employs organic semiconductors that can convert electricity to light, but also an electrolyte that further enhances the electronic properties of the semiconductor by allowing it to be electrochemically doped. This allows light-emitting films to be driven by a low-voltage source at a high efficiency. Unfortunately, the electrolyte has been shown to facilitate rapid degradation of the device under operation, which has historically severely limited the operational lifetime. Realizing the predicted high efficiency has also proven difficult. The purpose of this thesis is to bridge the gap between the LEC and the CFL. This is done by demonstrating efficient devices and improved operational lifetimes. Possible degradation mechanisms are identified and minimized using novel device architectures and optimized active layer compositions. An encapsulation method is presented, and shown to increase the LEC stability significantly by protecting it from ambient oxygen and water. The thesis further focuses on up-scaled fabrication under ambient air conditions, proving that light-emitting devices are compatible with solution-based and cost-efficient printing. This is achieved by a roll-to-roll compatible slot-die coating and a novel spray-depositing technique that alleviates problems stemming from dust particles and phase separation. A practical ambient air fabrication and a subsequent operation of light-emitting electrochemical cells with high efficiency are thus shown possible.

 

Place, publisher, year, edition, pages
Umeå: Umeå universitet , 2013. , 61 p.
Keyword [en]
Light-emitting electrochemical cell, fabrication, organic semiconductors, organic electronics, ambient fabrication, roll-to-roll
National Category
Atom and Molecular Physics and Optics
Research subject
Physics
Identifiers
URN: urn:nbn:se:umu:diva-79544ISBN: 978-91-7459-691-5 (print)OAI: oai:DiVA.org:umu-79544DiVA: diva2:642494
Public defence
2013-09-13, N300, Umeå universitet, Umeå, 09:47 (English)
Opponent
Supervisors
Available from: 2013-08-23 Created: 2013-08-22 Last updated: 2013-08-22Bibliographically approved
List of papers
1. Encapsulating light-emitting electrochemical cells for improved performance
Open this publication in new window or tab >>Encapsulating light-emitting electrochemical cells for improved performance
Show others...
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
2. Ambient fabrication of flexible and large-area organic light-emitting devices using slot-die coating
Open this publication in new window or tab >>Ambient fabrication of flexible and large-area organic light-emitting devices using slot-die coating
2012 (English)In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 3, 1002- p.Article in journal (Refereed) Published
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.

National Category
Physical Sciences
Identifiers
urn:nbn:se:umu:diva-61219 (URN)10.1038/ncomms2002 (DOI)000308801100018 ()
Available from: 2012-11-08 Created: 2012-11-07 Last updated: 2017-12-07Bibliographically approved
3. Yellow-green light-emitting electrochemical cells with long lifetime and high efficiency
Open this publication in new window or tab >>Yellow-green light-emitting electrochemical cells with long lifetime and high efficiency
2010 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 96, no 5, 053303- p.Article in journal (Refereed) Published
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.”

Identifiers
urn:nbn:se:umu:diva-35841 (URN)10.1063/1.3299018 (DOI)000274319500102 ()
Available from: 2010-09-07 Created: 2010-09-07 Last updated: 2013-08-22Bibliographically approved
4. Separating ion and and electron transport: the bi-layer light-emitting electrochemical cell
Open this publication in new window or tab >>Separating ion and and electron transport: the bi-layer light-emitting electrochemical cell
2010 (English)In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 132, no 19, 6646-6647 p.Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
ACS Publications, 2010
Identifiers
urn:nbn:se:umu:diva-35843 (URN)10.1021/ja102038e (DOI)000277721500017 ()
Available from: 2010-09-07 Created: 2010-09-07 Last updated: 2013-08-22Bibliographically approved
5. A Solution-Processed Trilayer Electrochemical Device: Localizing the Light Emission for Optimized Performance
Open this publication in new window or tab >>A Solution-Processed Trilayer Electrochemical Device: Localizing the Light Emission for Optimized Performance
2012 (English)In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 134, no 34, 14050-14055 p.Article in journal (Refereed) Published
Abstract [en]

We present a solution-processed trilayer light-emitting device architecture, comprising two hydrophobic and mobile-ion-containing "transport layers" sandwiching a hydrophilic and ion-free "intermediate layer", which allows for lowered self-absorption, minimized electrode quenching, and tunable light emission. Our results reveal that the transport layers can be doped in situ when a voltage is applied, that the intermediate layer as desired can contribute significantly to the light emission, and that the key to a successful operation is the employment of a porous and (similar to 5-10 nm) thin intermediate layer allowing for facile ion transport. We report that such a solution-processed device, comprising a thick trilayer material (similar to 250 nm) and air-stable electrodes, emits blue light (lambda(peak) = 450, 484 nm) with high efficiency (5.3 cd/A) at a low drive voltage of 5 V.

National Category
Physical Sciences
Identifiers
urn:nbn:se:umu:diva-61213 (URN)10.1021/ja3041916 (DOI)000308043400027 ()
Available from: 2012-11-08 Created: 2012-11-07 Last updated: 2017-12-07Bibliographically approved

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