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Publications (10 of 17) Show all publications
Zhang, X., Ràfols-Ribé, J., Mindemark, J., Tang, S., Lindh, M., Gracia-Espino, E., . . . Edman, L. (2024). Efficiency roll-off in light-emitting electrochemical cells. Advanced Materials
Open this publication in new window or tab >>Efficiency roll-off in light-emitting electrochemical cells
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2024 (English)In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095Article in journal (Refereed) Epub ahead of print
Abstract [en]

Understanding “efficiency roll-off” (i.e., the drop in emission efficiency with increasing current) is critical if efficient and bright emissive technologies are to be rationally designed. Emerging light-emitting electrochemical cells (LECs) can be cost- and energy-efficiently fabricated by ambient-air printing by virtue of the in situ formation of a p-n junction doping structure. However, this in situ doping transformation renders a meaningful efficiency analysis challenging. Herein, a method for separation and quantification of major LEC loss factors, notably the outcoupling efficiency and exciton quenching, is presented. Specifically, the position of the emissive p-n junction in common singlet-exciton emitting LECs is measured to shift markedly with increasing current, and the influence of this shift on the outcoupling efficiency is quantified. It is further verified that the LEC-characteristic high electrochemical-doping concentration renders singlet-polaron quenching (SPQ) significant already at low drive current density, but also that SPQ increases super-linearly with increasing current, because of increasing polaron density in the p-n junction region. This results in that SPQ dominates singlet-singlet quenching for relevant current densities, and significantly contributes to the efficiency roll-off. This method for deciphering the LEC efficiency roll-off can contribute to a rational realization of all-printed LEC devices that are efficient at highluminance.

Place, publisher, year, edition, pages
John Wiley & Sons, 2024
Keywords
efficiency roll-off, light-emitting electrochemical cell, p-n junction position, singlet-polaron quenching, singlet-singlet quenching
National Category
Atom and Molecular Physics and Optics Materials Chemistry
Identifiers
urn:nbn:se:umu:diva-220016 (URN)10.1002/adma.202310156 (DOI)001143796900001 ()38211953 (PubMedID)2-s2.0-85182424168 (Scopus ID)
Funder
Swedish Research Council, 2019-02345Swedish Research Council, 2021-04778Swedish Energy Agency, 50779-1Swedish Energy Agency, P2021-00032Bertil & Britt Svenssons Stiftelse för BelysningsteknikThe Kempe FoundationsKnut and Alice Wallenberg Foundation, KAW 2022.0381Knut and Alice Wallenberg Foundation, WISE-AP01-D02EU, European Research Council, 101096650
Available from: 2024-01-30 Created: 2024-01-30 Last updated: 2024-01-30
Auroux, E., Huseynova, G., Ràfols-Ribé, J., Miranda la Hera, V. & Edman, L. (2023). A metal-free and transparent light-emitting device by sequential spray-coating fabrication of all layers including PEDOT:PSS for both electrodes. RSC Advances, 13(25), 16943-16951
Open this publication in new window or tab >>A metal-free and transparent light-emitting device by sequential spray-coating fabrication of all layers including PEDOT:PSS for both electrodes
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2023 (English)In: RSC Advances, E-ISSN 2046-2069, Vol. 13, no 25, p. 16943-16951Article in journal (Refereed) Published
Abstract [en]

The concept of a metal-free and all-organic electroluminescent device is appealing from both sustainability and cost perspectives. Herein, we report the design and fabrication of such a light-emitting electrochemical cell (LEC), comprising a blend of an emissive semiconducting polymer and an ionic liquid as the active material sandwiched between two poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) conducting-polymer electrodes. In the off-state, this all-organic LEC is highly transparent, and in the on-state, it delivers uniform and fast to turn-on bright surface emission. It is notable that all three device layers were fabricated by material- and cost-efficient spray-coating under ambient air. For the electrodes, we systematically investigated and developed a large number of PEDOT:PSS formulations. We call particular attention to one such p-type doped PEDOT:PSS formulation that was demonstrated to function as the negative cathode, as well as future attempts towards all-organic LECs to carefully consider the effects of electrochemical doping of the electrode in order to achieve optimum device performance.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2023
National Category
Materials Chemistry
Identifiers
urn:nbn:se:umu:diva-211794 (URN)10.1039/d3ra02520a (DOI)001000925700001 ()37288374 (PubMedID)2-s2.0-85162809423 (Scopus ID)
Funder
Swedish Research Council, 2021-04778Swedish Research Council, 2019- 02345Swedish Energy Agency, 50779-1Bertil & Britt Svenssons Stiftelse för Belysningsteknik, 2022 höst-31The Kempe Foundations, SMK-1956Carl Tryggers foundation , CTS 19:86
Available from: 2023-07-12 Created: 2023-07-12 Last updated: 2023-07-12Bibliographically approved
Huseynova, G., Ràfols-Ribé, J., Auroux, E., Huang, P., Tang, S., Larsen, C. & Edman, L. (2023). Chemical doping to control the in-situ formed doping structure in light-emitting electrochemical cells. Scientific Reports, 13(1), Article ID 11457.
Open this publication in new window or tab >>Chemical doping to control the in-situ formed doping structure in light-emitting electrochemical cells
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2023 (English)In: Scientific Reports, E-ISSN 2045-2322, Vol. 13, no 1, article id 11457Article in journal (Refereed) Published
Abstract [en]

The initial operation of a light-emitting electrochemical cell (LEC) constitutes the in-situ formation of a p-n junction doping structure in the active material by electrochemical doping. It has been firmly established that the spatial position of the emissive p-n junction in the interelectrode gap has a profound influence on the LEC performance because of exciton quenching and microcavity effects. Hence, practical strategies for a control of the position of the p-n junction in LEC devices are highly desired. Here, we introduce a "chemical pre-doping" approach for the rational shifting of the p-n junction for improved performance. Specifically, we demonstrate, by combined experiments and simulations, that the addition of a strong chemical reductant termed "reduced benzyl viologen" to a common active-material ink during LEC fabrication results in a filling of deep electron traps and an associated shifting of the emissive p-n junction from the center of the active material towards the positive anode. We finally demonstrate that this chemical pre-doping approach can improve the emission efficiency and stability of a common LEC device.

Place, publisher, year, edition, pages
Springer Nature, 2023
National Category
Materials Chemistry
Identifiers
urn:nbn:se:umu:diva-212310 (URN)10.1038/s41598-023-38006-y (DOI)37454107 (PubMedID)2-s2.0-85164758513 (Scopus ID)
Funder
Carl Tryggers foundation The Kempe FoundationsSwedish Research CouncilSwedish Energy AgencyOlle Engkvists stiftelseBertil & Britt Svenssons Stiftelse för BelysningsteknikKnut and Alice Wallenberg Foundation
Available from: 2023-07-25 Created: 2023-07-25 Last updated: 2023-07-25Bibliographically approved
Ràfols-Ribé, J., Hänisch, C., Larsen, C., Reineke, S. & Edman, L. (2023). In situ determination of the orientation of the emissive dipoles in light-emitting electrochemical cells. Advanced Materials Technologies, 8(13), Article ID 2202120.
Open this publication in new window or tab >>In situ determination of the orientation of the emissive dipoles in light-emitting electrochemical cells
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2023 (English)In: Advanced Materials Technologies, E-ISSN 2365-709X, Vol. 8, no 13, article id 2202120Article in journal (Refereed) Published
Abstract [en]

The orientation of the emissive dipoles in thin-film devices is important since it strongly affects the light outcoupling and thereby the device emission efficiency. The light-emitting electrochemical cell (LEC) is particularly interesting in this context because its emissive dipoles are located in a high electric-field p-n junction, which is formed in situ by redistribution of bulky ions. This implies that the dipole orientation could be distinctly different in the driven LEC compared to the pristine device. This study develops the destructive-interference microcavity method for the accurate in situ determination of the orientation of the emissive dipoles during LEC operation and apply it on a common LEC device comprising an amorphous conjugated polymer termed Super Yellow as the emitter. It is found that ≈95% of the emissive dipoles are oriented in the horizontal direction with respect to the thin-film plane in both the pristine LEC and during steady-state light emission. This finding is attractive since it enables for efficient outcoupling of the generated photons, and interesting because it shows that a horizontal orientation of the emissive dipoles can remain despite the existence of a strong perpendicular electric field and the nearby motion of bulky ions during LEC operation.

Place, publisher, year, edition, pages
John Wiley & Sons, 2023
Keywords
anisotropy, device efficiency, dipole orientation, light-emitting electrochemical cells, Super Yellow
National Category
Atom and Molecular Physics and Optics Condensed Matter Physics
Identifiers
urn:nbn:se:umu:diva-206790 (URN)10.1002/admt.202202120 (DOI)000963273400001 ()2-s2.0-85151955762 (Scopus ID)
Funder
The Kempe FoundationsSwedish Research CouncilSwedish Energy AgencyOlle Engkvists stiftelseWenner-Gren FoundationsBertil & Britt Svenssons Stiftelse för Belysningsteknik
Available from: 2023-04-24 Created: 2023-04-24 Last updated: 2023-11-03Bibliographically approved
Tang, S., dos Santos, J. M., Ràfols-Ribé, J., Wang, J., Zysman-Colman, E. & Edman, L. (2023). Introducing MR-TADF emitters into light-emitting electrochemical cells for narrowband and efficient emission. Advanced Functional Materials, 33, Article ID 2306170.
Open this publication in new window or tab >>Introducing MR-TADF emitters into light-emitting electrochemical cells for narrowband and efficient emission
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2023 (English)In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 33, article id 2306170Article in journal (Refereed) Published
Abstract [en]

Organic semiconductors that emit by the process of multi-resonance thermally activated delayed fluorescence (MR-TADF) can deliver narrowband and efficient electroluminescence while being processable from solvents and metal-free. This renders them attractive for use as the emitter in sustainable light-emitting electrochemical cells (LECs), but so far reports of narrowband and efficient MR-TADF emission from LEC devices are absent. Here, this issue is addressed through careful and systematic material selection and device development. Specifically, the authors show that the detrimental aggregation tendency of an archetypal rigid and planar carbazole-based MR-TADF emitter can be inhibited by its dispersion into a compatible carbazole-based blend host and an ionic-liquid electrolyte, and it is further demonstrated that the tuning of this active material results in a desired balanced p- and n-type electrochemical doping, a high solid-state photoluminescence quantum yield of 91%, and singlet and triplet trapping on the MR-TADF guest emitter. The introduction of this designed metal-free active MR-TADF material into a LEC, employing air-stabile electrodes, results in bright blue electroluminescence of 500 cd m−2, which is delivered at a high external quantum efficiency of 3.8% and shows a narrow emission profile with a full-width-at-half-maximum of 31 nm.

Place, publisher, year, edition, pages
Wiley-VCH Verlagsgesellschaft, 2023
Keywords
blue emission, high efficiency, light-emitting electrochemical cells, multi-resonance thermally activated delayed fluorescence, narrowband emission
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:umu:diva-214037 (URN)10.1002/adfm.202306170 (DOI)001054087300001 ()2-s2.0-85168601283 (Scopus ID)
Funder
Swedish Research CouncilSwedish Energy AgencyBertil & Britt Svenssons Stiftelse för BelysningsteknikThe Kempe FoundationsOlle Engkvists stiftelseWenner-Gren Foundations
Available from: 2023-09-06 Created: 2023-09-06 Last updated: 2023-12-29Bibliographically approved
Liu, Y.-f., Tang, S., Gao, Z., Shao, X., Zhu, X., Ràfols-Ribé, J., . . . Wang, J. (2023). The influence of the capping ligands on the optoelectronic performance, morphology, and ion liberation of CsPbBr3 perovskite quantum dots. Nano Reseach, 16(7), 10626-10633
Open this publication in new window or tab >>The influence of the capping ligands on the optoelectronic performance, morphology, and ion liberation of CsPbBr3 perovskite quantum dots
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2023 (English)In: Nano Reseach, ISSN 1998-0124, E-ISSN 1998-0000, Vol. 16, no 7, p. 10626-10633Article in journal (Refereed) Published
Abstract [en]

Perovskite quantum dots (PeQDs) endowed with capping ligands exhibit impressive optoelectronic properties and enable for cost-efficient solution processing and exciting application opportunities. We synthesize and characterize three different PeQDs with the same cubic CsPbBr3 core, but which are distinguished by the ligand composition and density. PeQD-1 features a binary didodecyldimethylammonium bromide (DDAB) and octanoic acid capping ligand system, with a high surface density of 1.53 nm−2, whereas PeQD-2 and PeQD-3 are coated by solely DDAB at a gradually lower surface density. We show that PeQD-1 endowed with highest ligand density features the highest dispersibility in toluene of 150 g/L, the highest photoluminescence quantum yield of 95% in dilute solution and 59% in a neat film, and the largest core-to-core spacing in neat thin films. We further establish that ions are released from the core of PeQD-1 when it is exposed to an electric field, although it comprises a dense coating of one capping ligand per four surface core atoms. We finally exploit these combined findings to the development of a light-emitting electrochemical cell (LEC), where the active layer is composed solely of solution-processed pure PeQDs, without additional electrolytes. In this device, the ion release is utilized as an advantage for the electrochemical doping process and efficient emissive operation of the LEC.

Place, publisher, year, edition, pages
Springer Nature, 2023
Keywords
CsPbBr3 quantum dots, capping ligand, ion liberation, light-emitting electrochemical cell
National Category
Materials Engineering Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:umu:diva-205540 (URN)10.1007/s12274-023-5589-y (DOI)000975366100001 ()2-s2.0-85151659595 (Scopus ID)
Funder
Swedish Energy Agency, 45419-1Swedish Energy Agency, 46523-1Swedish Energy Agency, 50779-1Swedish Research Council, 2018-03937Swedish Research Council, 2019-02345Swedish Research Council, 2020-04437Swedish Foundation for Strategic ResearchOlle Engkvists stiftelse, 186-0637Olle Engkvists stiftelse, 193-0578Bertil & Britt Svenssons Stiftelse för Belysningsteknik
Available from: 2023-03-08 Created: 2023-03-08 Last updated: 2023-12-06Bibliographically approved
Ràfols-Ribé, J., Zhang, X., Larsen, C., Lundberg, P., Lindh, E. M., Mai, C. T., . . . Edman, L. (2022). Controlling the emission zone by additives for improved light‐emitting electrochemical cells. Advanced Materials, 34(8), Article ID 2107849.
Open this publication in new window or tab >>Controlling the emission zone by additives for improved light‐emitting electrochemical cells
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2022 (English)In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 34, no 8, article id 2107849Article in journal (Refereed) Published
Abstract [en]

The position of the emission zone (EZ) in the active material of a light-emitting electrochemical cell (LEC) has a profound influence on its performance because of microcavity effects and doping- and electrode-induced quenching. Previous attempts of EZ control have focused on the two principal constituents in the active material—the organic semiconductor (OSC) and the mobile ions—but this study demonstrates that it is possible to effectively control the EZ position through the inclusion of an appropriate additive into the active material. More specifically, it is shown that a mere modification of the end group on an added neutral compound, which also functions as an ion transporter, results in a shifted EZ from close to the anode to the center of the active material, which translates into a 60% improvement of the power efficiency. This particular finding is rationalized by a lowering of the effective electron mobility of the OSC through specific additive: OSC interactions, but the more important generic conclusion is that it is possible to control the EZ position, and thereby the LEC performance, by the straightforward inclusion of an easily tuned additive in the active material.

Place, publisher, year, edition, pages
Wiley-VCH Verlagsgesellschaft, 2022
National Category
Physical Sciences
Identifiers
urn:nbn:se:umu:diva-201531 (URN)10.1002/adma.202107849 (DOI)000742703700001 ()34891219 (PubMedID)2-s2.0-85122826739 (Scopus ID)
Funder
The Kempe FoundationsSwedish Research CouncilSwedish Energy AgencySwedish Foundation for Strategic ResearchOlle Engkvists stiftelseWenner-Gren FoundationsBertil & Britt Svenssons Stiftelse för Belysningsteknik
Available from: 2022-12-07 Created: 2022-12-07 Last updated: 2022-12-07Bibliographically approved
Tang, S., Lundberg, P., Tsuchiya, Y., Ràfols-Ribé, J., Liu, Y.-f., Wang, J., . . . Edman, L. (2022). Efficient and bright blue thermally activated delayed fluorescence from light-emitting electrochemical cells. Advanced Functional Materials (44), Article ID 2205967.
Open this publication in new window or tab >>Efficient and bright blue thermally activated delayed fluorescence from light-emitting electrochemical cells
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2022 (English)In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, no 44, article id 2205967Article in journal (Refereed) Published
Abstract [en]

Light-emitting electrochemical cells (LECs) comprising metal-free molecules that emit by the process of thermally activated delayed fluorescence (TADF) can be both sustainable and low cost. However, the blue emission performance of current TADF-LECs is unfortunately poor, which effectively prohibits their utilization in important applications, such as illumination and full-color displays. Here, this drawback is addressed through the development of a TADF-LEC, which delivers blue light emission (peak wavelength = 475 nm) with a high external quantum efficiency of 5.0%, corresponding to a current efficacy of 9.6 cd A-1. It is notable that this high efficiency is attained at bright luminance of 740 cd m-2, and that the device turn-on is very fast. It is demonstrated that this accomplishment is enabled by the blending of a carbazole-based 9-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)-2-methylphenyl)-3,6-dimethyl-9H-carbazole guest emitter with a compatible carbazole-based tris(4-carbazoyl-9-ylphenyl)amine:2,6-bis(3-(carbazol-9-yl)phenyl)pyridine blend-host for the attainment of bipolar electrochemical doping, balanced electron/hole transport, and exciplex-effectuated host-to-guest energy transfer.

Place, publisher, year, edition, pages
John Wiley & Sons, 2022
Keywords
blend host, blue emission, high efficiency, light-emitting electrochemical cells, thermally activated delayed fluorescence
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:umu:diva-198933 (URN)10.1002/adfm.202205967 (DOI)000839564400001 ()2-s2.0-85135775851 (Scopus ID)
Funder
The Kempe FoundationsSwedish Research CouncilSwedish Energy AgencySwedish Foundation for Strategic ResearchWenner-Gren FoundationsBertil & Britt Svenssons Stiftelse för Belysningsteknik
Available from: 2022-09-16 Created: 2022-09-16 Last updated: 2022-11-25Bibliographically approved
Auroux, E., Park, S.-R., Ràfols-Ribé, J. & Edman, L. (2022). Ion transfer into solution-processed electrodes can significantly shift the p-n junction and emission efficiency of light-emitting electrochemical cells. Applied Physics Letters, 121(23), Article ID 231102.
Open this publication in new window or tab >>Ion transfer into solution-processed electrodes can significantly shift the p-n junction and emission efficiency of light-emitting electrochemical cells
2022 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 121, no 23, article id 231102Article in journal (Refereed) Published
Abstract [en]

A light-emitting electrochemical cell (LEC) comprises mobile ions in its active material, which enable for in situ formation of a p-n junction by electrochemical doping. The position of this emissive p-n junction in the interelectrode gap is important, because it determines whether the emission is affected by constructive or destructive interference. An appealing LEC feature is that the entire device can be fabricated by low-cost solution-based printing and coating. Here, we show, somewhat unexpectedly, that the replacement of conventional vacuum-deposited indium-tin-oxide (ITO) for the positive anode with solution-processed poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) can result in an increase in the peak light-emission output by 75%. We demonstrate that this emission increase is due to that the p-n junction shifts from a position of destructive interference in the center of the interelectrode gap with ITO to a position of constructive interference closer to the anode with PEDOT:PSS. We rationalize the anodic p-n junction shift by significant anion transfer into the soft and porous PEDOT:PSS electrode during LEC operation, which is prohibited for the ITO electrode because of its compact and hard nature. Our study, thus, contributes with important design criteria for the attainment of efficient light emission from solution-processed LEC devices.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2022
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:umu:diva-202064 (URN)10.1063/5.0123469 (DOI)000894763400004 ()2-s2.0-85144449170 (Scopus ID)
Available from: 2023-01-03 Created: 2023-01-03 Last updated: 2023-09-05Bibliographically approved
Larsen, C., Lundberg, P., Tang, S., Ràfols-Ribé, J., Sandström, A., Lindh, E. M., . . . Edman, L. (2021). A tool for identifying green solvents for printed electronics. Nature Communications, 12, Article ID 4510.
Open this publication in new window or tab >>A tool for identifying green solvents for printed electronics
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2021 (English)In: Nature Communications, E-ISSN 2041-1723, Vol. 12, article id 4510Article in journal (Refereed) Published
Abstract [en]

The emerging field of printed electronics uses large amounts of printing and coating solvents during fabrication, which commonly are deposited and evaporated within spaces available to workers. It is in this context unfortunate that many of the currently employed solvents are non-desirable from health, safety, or environmental perspectives. Here, we address this issue through the development of a tool for the straightforward identification of functional and "green" replacement solvents. In short, the tool organizes a large set of solvents according to their Hansen solubility parameters, ink properties, and sustainability descriptors, and through systematic iteration delivers suggestions for green alternative solvents with similar dissolution capacity as the current non-sustainable solvent. We exemplify the merit of the tool in a case study on a multi-solute ink for high-performance light-emitting electrochemical cells, where a non-desired solvent was successfully replaced by two benign alternatives. The green-solvent selection tool is freely available at: www.opeg-umu.se/green-solvent-tool.

Place, publisher, year, edition, pages
Nature research, 2021
National Category
Other Physics Topics
Identifiers
urn:nbn:se:umu:diva-170536 (URN)10.1038/s41467-021-24761-x (DOI)000680504900010 ()34301943 (PubMedID)2-s2.0-85111109535 (Scopus ID)
Note

Originally included in thesis in manuscript form.

Available from: 2020-05-07 Created: 2020-05-07 Last updated: 2023-03-28Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0003-1256-149x

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