Digitala Vetenskapliga Arkivet

Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Light for a brighter morrow: paving the way for sustainable light-emitting devices
Umeå University, Faculty of Science and Technology, Department of Physics. (The Organic Electronics and Photonics Group)ORCID iD: 0000-0003-3481-5163
2020 (English)Doctoral thesis, comprehensive summary (Other academic)Alternative title
Ljus för en ljusare morgondag : banar väg för hållbara ljuskällor (Swedish)
Abstract [en]

We live in an artificially lit world, where light enhances our productivity and improves our quality of life. Today our appetite for light is stronger than ever, and emerging light-emitting technologies do not just replace the classical incandescent light bulb, they also open up for a new world of applications. The problem is that our environment does not cope with the increased energy demand during fabrication and usage, and the insufficient recycling that currently follows this rapid technological development. We must therefore adapt, and from here on out consider the entire environmental footprint and the necessity of our devices. Organic electronics has the potential to become sustainable. It allows for cheap and energy-efficient fabrication methods, using abundant materials, mainly carbon. Such sophisticated conductive plastics can be made thin and flexible, and they are thereby very versatile. It is in this context that we find the light-emitting electrochemical cell (LEC)—a strong contender for affordable and sustainable light. The LEC has a simple device design that is fit for solution based fabrication and new useful applications in, for example, medicine. The simple LEC design is enabled by its operational mechanism, where mobile ions aid electronic charge injection and improves electric conductivity by electrochemical doping. However, this dynamic nature complicates the attainment of devices that are efficient, bright, and retain a long lifetime. Herein, we face these challenges with sustainability as the beacon. We find that careful design of the active material, and selection of its constituents, can lead to LECs that are both efficient and bright. Importantly we show that this is attainable with entirely organic active materials, via thermally activated delayed fluorescence; thereby moving away from unsustainable phosphorescent emitters that contain problematic rare metals. With large-scale manufacturing in mind, we introduce a tool that identifies environmentally benign and functional solvents. Furthermore we design and validate a realistic optical model that unveils the common optical loss mechanisms in LECs. The insights gained guide the optical design of highly efficient LECs in the transition towards an upscaled production.I hope that the progress made will contribute to a road map for the design of sustainable light-emitting devices. It is then our responsibility, as a society, to make use of them where needed.

Abstract [sv]

Vår värld är fylld av ljuskällor som bidrar till både vår livskvalitet och produktivitet. Idag är suget efter ljus större än någonsin, då nya ljuskällor inte bara ersätterde gamla, utan öppnar även upp för helt nya användningsområden. Problemet är att vår miljö inte klarar av den höga energiförbrukningen och bristfälliga återvinningen, som följer den ökade användningen. Vi måste därför anpassa oss, och se över det totala miljöavtrycket från både tillverkning och användning av våra produkter. En hållbar lösning kan vara organisk elektronik. Denna teknik möjliggör för billig och energieffektiv tillverkning, och baseras på vanligt förekommande ämnen, främst kol. Dessa elektriskt ledande plaster kan göras både tunna och böjbara och är därmed väldigt anpassningsbara. En så kallad ljusemitterande elektrokemisk cell (LEC) har en förhållandevis enkel konstrution. Den lämpar sig för energisnål tillverkning, och för nya användningsområden inom exempelvis medicin. En LECs enkla konstruktion är möjlig tack vare rörliga joner i det aktiva materialet. Jonerna möjliggör injektion av elektroniska laddningar till det aktiva materialet och förbättrar dess elektriska ledningsförmåga genom elektrokemisk dopning. Dynamiken i det aktiva materialet försvårar dock utvecklingen — det är svårt att få fram komponenter med hög effektivitet och ljusstyrka, som samtidigt har en lång livslängd. I denna avhandling tar vi oss an dessa utmaningar med hållbarhet som ledord. Vi visar att noggrant utvalda material, och design av det aktiva materialet, kan göra att en LEC blir både ljusstark och effektiv. Vi visar dessutom att detta inte kräver ohållbara fosforescerande material, som ofta innehåller problematiska ädelmetaller, utan att det är möjligt från helt organiska material via termiskt aktiverad fördröjd fluorescens. Framtidsbilden för en LEC är storskalig tillverkning, men för en sådan krävs också stora mängder lösningsmedel. Med detta i åtanke har vi skapat ett verktyg för att identifiera lämpliga miljövänliga lösningsmedel. Dessutom har vi utvecklat en realistiskoptisk beräkningsmodell med god experimentell överrensstämmelse. Modellen ger oss en bättre förståelse för de olika optiska förlustkanalerna i en LEC, vilket är viktigt för att bibehålla deras prestanda i övergången till storskalig tillverkning. Jag hoppas att vägen vi banat kommer skynda på utvecklingen av hållbara ljuskällor samt att vi alla tar vårat ansvar och ser till att de används på ett ansvarsfullt sätt.

Place, publisher, year, edition, pages
Umeå: Umeå universitet , 2020. , p. 54
Keywords [en]
Artificial Light, Organic Electronics, Photophysics, Light-emitting Electrochemical Cells, Thermally Activated Delayed Fluorescence, Host-Guest, Sustainability, Solution Processing
National Category
Nano Technology Condensed Matter Physics Other Physics Topics
Research subject
Physics
Identifiers
URN: urn:nbn:se:umu:diva-170454ISBN: 978-91-7855-243-6 (print)ISBN: 978-91-7855-244-3 (electronic)OAI: oai:DiVA.org:umu-170454DiVA, id: diva2:1429241
Public defence
2020-06-05, MA121, MIT-huset, Umeå, 09:00 (English)
Opponent
Supervisors
Available from: 2020-05-15 Created: 2020-05-08 Last updated: 2020-05-12Bibliographically approved
List of papers
1. Toward Efficient and Metal-Free Emissive Devices: A Solution Processed Host Guest Light-Emitting Electrochemical Cell Featuring Thermally Activated Delayed Fluorescence
Open this publication in new window or tab >>Toward Efficient and Metal-Free Emissive Devices: A Solution Processed Host Guest Light-Emitting Electrochemical Cell Featuring Thermally Activated Delayed Fluorescence
2017 (English)In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 9, no 34, p. 28810-28816Article in journal (Refereed) Published
Abstract [en]

The next generation of emissive devices should preferably be efficient, low-cost, and environmentally sustainable, and as such utilize all electrically generated excitons (both singlets and triplets) for the light emission, while being free from rare metals such as iridium. Here, we report on a step toward this vision through the design, fabrication, and operation of a host guest light-emitting electrochemical cell (LEC) featuring an organic thermally activated delayed fluorescence (TADF) guest that harvests both singlet and triplet excitons for the emission. The rare-metal-free active material also consists of a polymeric electrolyte and a polymeric compatibilizer for the facilitation of a cost-efficient and scalable solution-based fabrication, and for the use of air-stable electrodes. We report that such TADF-LEC devices can deliver uniform green light emission with a maximum luminance of 228 cd m(-2) when driven by a constant-current density of 770 A m(-2), and 760 cd m(-2) during a voltage ramp, which represents a one-order-of-magnitude improvement in comparison to previous TADF-emitting LECs.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 2017
Keywords
light-emitting electrochemical cell, thermally activated delayed fluorescence, low-cost solution ocessing. efficient and metal-free emitter, sustainable illumination technology, XTER DL, 1953, JOURNAL OF CHEMICAL PHYSICS, V21, P836 erster Theodor, 2012, JOURNAL OF BIOMEDICAL OPTICS, V17, leur B., 2013, Molecular Fluorescence, iend RH, 1999, NATURE, V397, P121 tyba Piotr, 2011, ACS NANO, V5, P574 ng Zhehan, 2015, ECONOMIC GEOLOGY, V110, P1925
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:umu:diva-140478 (URN)10.1021/acsami.7b07826 (DOI)000409395500075 ()28762717 (PubMedID)
Available from: 2017-10-23 Created: 2017-10-23 Last updated: 2020-05-08Bibliographically approved
2. Design rules for light-emitting electrochemical cells delivering bright luminance at 27.5 percent external quantum efficiency
Open this publication in new window or tab >>Design rules for light-emitting electrochemical cells delivering bright luminance at 27.5 percent external quantum efficiency
Show others...
2017 (English)In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 8, article id 1190Article in journal (Refereed) Published
Abstract [en]

The light-emitting electrochemical cell promises cost-efficient, large-area emissive applications, as its characteristic in-situ doping enables use of air-stabile electrodes and a solution-processed single-layer active material. However, mutual exclusion of high efficiency and high brightness has proven a seemingly fundamental problem. Here we present a generic approach that overcomes this critical issue, and report on devices equipped with air-stabile electrodes and outcoupling structure that deliver a record-high efficiency of 99.2 cd A(-1) at a bright luminance of 1910 cd m(-2). This device significantly outperforms the corresponding optimized organic light-emitting diode despite the latter employing calcium as the cathode. The key to this achievement is the design of the host-guest active material, in which tailored traps suppress exciton diffusion and quenching in the central recombination zone, allowing efficient triplet emission. Simultaneously, the traps do not significantly hamper electron and hole transport, as essentially all traps in the transport regions are filled by doping.

Place, publisher, year, edition, pages
Nature Publishing Group, 2017
National Category
Other Physics Topics Condensed Matter Physics
Identifiers
urn:nbn:se:umu:diva-141807 (URN)10.1038/s41467-017-01339-0 (DOI)000413894100012 ()29085078 (PubMedID)
Available from: 2017-11-27 Created: 2017-11-27 Last updated: 2020-05-08Bibliographically approved
3. Thermally activated delayed fluorescence with 7% external quantum efficiency from a light-emitting electrochemical cell
Open this publication in new window or tab >>Thermally activated delayed fluorescence with 7% external quantum efficiency from a light-emitting electrochemical cell
Show others...
2019 (English)In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 10, article id 5307Article in journal (Refereed) Published
Abstract [en]

We report on light-emitting electrochemical cells, comprising a solution-processed single-layer active material and air-stabile electrodes, that exhibit efficient and bright thermally activated delayed fluorescence. Our optimized devices delivers a luminance of 120 cd m−2 at an external quantum efficiency of 7.0%. As such, it outperforms the combined luminance/efficiency state-of-the art for thermally activated delayed fluorescence light-emitting electrochemical cells by one order of magnitude. For this end, we employed a polymeric blend host for balanced electrochemical doping and electronic transport as well as uniform film formation, an optimized concentration (<1 mass%) of guest for complete host-to-guest energy transfer at minimized aggregation and efficient emission, and an appropriate concentration of an electrochemically stabile electrolyte for desired doping effects. The generic nature of our approach is manifested in the attainment of bright and efficient thermally activated delayed fluorescence emission from three different light-emitting electrochemical cells with invariant host:guest:electrolyte number ratio.

Place, publisher, year, edition, pages
Nature Publishing Group, 2019
National Category
Other Physics Topics
Identifiers
urn:nbn:se:umu:diva-166389 (URN)10.1038/s41467-019-13289-w (DOI)000498195100005 ()31757959 (PubMedID)2-s2.0-85075497295 (Scopus ID)
Available from: 2019-12-17 Created: 2019-12-17 Last updated: 2020-05-08Bibliographically approved
4. A Polymer Featuring Thermally Activated Delayed Fluorescence as Emitter in Light-Emitting Electrochemical Cells
Open this publication in new window or tab >>A Polymer Featuring Thermally Activated Delayed Fluorescence as Emitter in Light-Emitting Electrochemical Cells
Show others...
(English)Manuscript (preprint) (Other academic)
National Category
Other Physics Topics
Identifiers
urn:nbn:se:umu:diva-170537 (URN)
Available from: 2020-05-07 Created: 2020-05-07 Last updated: 2020-05-12
5. A tool for identifying green solvents for printed electronics
Open this publication in new window or tab >>A tool for identifying green solvents for printed electronics
Show others...
(English)Manuscript (preprint) (Other academic)
National Category
Other Physics Topics
Identifiers
urn:nbn:se:umu:diva-170536 (URN)
Available from: 2020-05-07 Created: 2020-05-07 Last updated: 2020-05-12
6. The Weak Microcavity as an Enabler for Bright and Fault-tolerant Light-emitting Electrochemical Cells
Open this publication in new window or tab >>The Weak Microcavity as an Enabler for Bright and Fault-tolerant Light-emitting Electrochemical Cells
Show others...
2018 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, article id 6970Article in journal (Refereed) Published
Abstract [en]

The light-emitting electrochemical cell (LEC) is functional at substantial active-layer thickness, and is as such heralded for being fit for low-cost and fault-tolerant solution-based fabrication. We report here that this statement should be moderated, and that in order to obtain a strong luminous output, it is fundamentally important to fabricate LEC devices with a designed thickness of the active layer. By systematic experimentation and simulation, we demonstrate that weak optical microcavity effects are prominent in a common LEC system, and that the luminance and efficiency, as well as the emission color and the angular intensity, vary in a periodic manner with the active-layer thickness. Importantly, we demonstrate that high-performance light-emission can be attained from LEC devices with a significant active-layer thickness of 300 nm, which implies that low-cost solution-processed LECs are indeed a realistic option, provided that the device structure has been appropriately designed from an optical perspective.

Place, publisher, year, edition, pages
Nature Publishing Group, 2018
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:umu:diva-147802 (URN)10.1038/s41598-018-25287-x (DOI)000431291500022 ()29725061 (PubMedID)
Note

Publisher Correction: M. Lindh, P. Lundberg, T. Lanz, J. Mindemark, L. Edman. The Weak Microcavity as an Enabler for Bright and Fault-tolerant Light-emitting Electrochemical Cells. Scientific Reports. 2018;8 DOI: 10.1038/s41598-018-26760-3

Available from: 2018-05-22 Created: 2018-05-22 Last updated: 2020-05-08Bibliographically approved
7. Optical analysis of light-emitting electrochemical cells
Open this publication in new window or tab >>Optical analysis of light-emitting electrochemical cells
2019 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 9, article id 10433Article in journal (Refereed) Published
Abstract [en]

The light-emitting electrochemical cell (LEC) is a contender for emerging applications of light, primarily because it offers low-cost solution fabrication of easily functionalized device architectures. The attractive properties originate in the in-situ formation of electrochemically doped transport regions that enclose an emissive intrinsic region, but the understanding of how this intricate doping structure affects the optical performance of the LEC is largely lacking. We combine angle- and doping-dependent measurements and simulations, and demonstrate that the emission zone in our high-performance LEC is centered at ~30% of the active-layer thickness (dal) from the anode. We further find that the emission intensity and efficiency are undulating with dal, and establish that the first emission maximum at dal ~ 100 nm is largely limited by the lossy coupling of excitons to the doping regions, whereas the most prominent loss channel at the second maximum at dal ~ 300 nm is wave-guided modes.

Place, publisher, year, edition, pages
Nature Publishing Group, 2019
National Category
Nano Technology Condensed Matter Physics
Identifiers
urn:nbn:se:umu:diva-156092 (URN)10.1038/s41598-019-46860-y (DOI)000475845400037 ()31320711 (PubMedID)2-s2.0-85069470003 (Scopus ID)
Note

Originally included in thesis in manuscript form.

Available from: 2019-02-05 Created: 2019-02-05 Last updated: 2020-05-08Bibliographically approved

Open Access in DiVA

fulltext(11417 kB)20 downloads
File information
File name FULLTEXT01.pdfFile size 11417 kBChecksum SHA-512
0956b7339ca1c25afc506f06856c5a645f5bdfd20c2e2ad32f1bf50db528e62cfe0b69cda705e06e0faf3df6642a1e66a65dea448b2d562015a7b6de38420a16
Type fulltextMimetype application/pdf
spikblad(368 kB)2 downloads
File information
File name SPIKBLAD01.pdfFile size 368 kBChecksum SHA-512
ba8fa1520e68a4c5eca19dad4e2bf41eff56258c51f3dc88677c7c20766acffa32306b7d31384f337c606654050a7edb458ec5224a3c9141f6a322108e50d53d
Type spikbladMimetype application/pdf

Search in DiVA

By author/editor
Lundberg, Petter
By organisation
Department of Physics
Nano TechnologyCondensed Matter PhysicsOther Physics Topics

Search outside of DiVA

GoogleGoogle Scholar
Total: 20 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 209 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf