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Jafari M, Pedersen JO, Barhemat S, Ederth T. In Situ Surface-Enhanced Raman Spectroscopy on Organic Mixed Ionic-Electronic Conductors: Tracking Dynamic Doping in Light-Emitting Electrochemical Cells. ACS APPLIED MATERIALS & INTERFACES 2024; 16:28938-28948. [PMID: 38780164 PMCID: PMC11163397 DOI: 10.1021/acsami.4c00684] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/12/2024] [Revised: 04/11/2024] [Accepted: 05/14/2024] [Indexed: 05/25/2024]
Abstract
In the domain of organic mixed ionic-electronic conductors (OMIECs), simultaneous transport and coupling of ionic and electronic charges are crucial for the function of electrochemical devices in organic electronics. Understanding conduction mechanisms and chemical reactions in operational devices is pivotal for performance enhancement and is necessary for the informed and systematic development of more promising materials. Surface-enhanced Raman spectroscopy (SERS) is a potent tool for monitoring electrochemical evolution and dynamic doping in operational devices, offering enhanced sensitivity to subtle spectral changes. We demonstrate the utility of SERS for in situ tracking of doping in OMIECs in an organic light-emitting electrochemical cell (LEC) containing a conjugated polymer (poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene]; MEH-PPV), a molecular anion (lithium triflate), and an electrolyte network (poly(ethylene oxide); PEO). SERS enhancement is achieved via an interleaved layer of gold particles formed by spontaneous breakup of a deposited thin gold film. The results successfully highlight the ability of SERS to unveil time-resolved MEH-PPV doping and polaron formation, elucidating the effects of triflate ion transfer in the operating device and validating the electrochemical doping model in LECs.
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Affiliation(s)
- Mohammad
Javad Jafari
- Division
of Biophysics and Bioengineering, IFM, Linköping
University, Linköping 581 83, Sweden
| | - Jonas Oshaug Pedersen
- Division
of Biophysics and Bioengineering, IFM, Linköping
University, Linköping 581 83, Sweden
| | - Samira Barhemat
- Department
of Vision Inspection, Mabema AB, Linköping 584 22, Sweden
| | - Thomas Ederth
- Division
of Biophysics and Bioengineering, IFM, Linköping
University, Linköping 581 83, Sweden
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2
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Tseng WS, Hsieh CS, Chan MC, Su HC. Non-invasive probing of dynamic ion migration in light-emitting electrochemical cells by an advanced nanoscale confocal microscope. OPTICS EXPRESS 2022; 30:28817-28828. [PMID: 36299070 DOI: 10.1364/oe.463352] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/09/2022] [Accepted: 07/14/2022] [Indexed: 06/16/2023]
Abstract
In this study, we firstly propose an optical approach to investigate the ion profile of organic films in light-emitting electrochemical cells (LECs) without any invasive sputtering processes. In contrast to previous literatures, this pure optical strategy allows us to record clear and non-destructive ion profile images in the (Ru(dtb-bpy)3(PF6)2) consisted organic layer without interferences of complex collisions from the bombardment of secondary sputter induced ions in a conventional time-of-flight secondary ion mass spectrometry. By using the advanced position sensitive detector (PSD)-based Nanoscale Confocal Microscope, ion distribution profiles were successfully acquired based on the observation of nanoscale optical path length difference by measuring the refractive-index variation while the thickness of the LEC layer was fixed. Dynamic time-dependent ion profile displayed clear ion migration process under a 100 V applied bias at two ends of the LEC. This technique opens up a new avenue towards the future investigations of ion distributions inside organic/inorganic materials, Li-ion batteries, or micro-fluid channels without damaging the materials or disturbing the device operation.
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3
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Shanmugasundaram K, Been H, John JC, Puthanveedu A, Pharm NNT, Lee SG, Choe Y. Simple luminescent phenanthroimidazole emitters for solution-processed non-doped organic light-emitting electrochemical cells. NEW J CHEM 2021. [DOI: 10.1039/d1nj02811a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Organic luminescent materials with leveraging properties have attracted urgent demand for their commercial application in lighting devices.
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Affiliation(s)
- Kanagaraj Shanmugasundaram
- School of Chemical and Biomolecular Engineering, Pusan National University, Busan 46241, Republic of Korea
| | - HyeIn Been
- School of Chemical and Biomolecular Engineering, Pusan National University, Busan 46241, Republic of Korea
| | - Jino C. John
- School of Chemical and Biomolecular Engineering, Pusan National University, Busan 46241, Republic of Korea
| | - Archana Puthanveedu
- School of Chemical and Biomolecular Engineering, Pusan National University, Busan 46241, Republic of Korea
| | - Nguyet N. T. Pharm
- School of Chemical and Biomolecular Engineering, Pusan National University, Busan 46241, Republic of Korea
| | - Seung Geol Lee
- School of Chemical and Biomolecular Engineering, Pusan National University, Busan 46241, Republic of Korea
- Department of Organic Material Science and Engineering, Pusan National University, Busan 46241, Republic of Korea
| | - Youngson Choe
- School of Chemical and Biomolecular Engineering, Pusan National University, Busan 46241, Republic of Korea
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4
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Birdee K, Hu S, Gao J. Strong Doping and Electroluminescence Realized by Fast Ion Transport through a Planar Polymer/Polymer Interface in Bilayer Light-Emitting Electrochemical Cells. ACS APPLIED MATERIALS & INTERFACES 2020; 12:46381-46389. [PMID: 32942853 DOI: 10.1021/acsami.0c13569] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Bilayer light-emitting electrochemical cells are demonstrated with a top conjugated polymer (CP) emitting layer and a solid polymer electrolyte (SPE) underlayer. Fast, long-range ion transport through the planar CP/SPE interface leads to doping and junction electroluminescence in the CP layer. All bilayer cells have pairs of aluminum electrodes separated by 2 or 11 mm at their inner edges, creating the largest planar (lateral) cells that can be imaged with excellent temporal and spatial resolutions. To understand how in situ electrochemical doping occurs in the CP layer without any ionic species mixed in, the planar bilayer cells are investigated for different CPs, CP layer thickness, operating voltage, and operating temperature. The bilayer cells are much faster to turn on than control cells made from a single mixed CP/SPE layer. The cell current and the doping propagation speed exhibit a linear dependence on the operating voltage and an Arrhenius-type temperature dependence. Unexpectedly, long-range ion transport in the CP layer and across the CP/SPE interface does not impede the doping reactions. Instead, the doping reactions are limited by the bulk resistance of the extra-wide SPE underlayer. In bilayer cells with a thin red-emitting CP layer, ion transport and doping reactions can penetrate the entire CP layer in the vertical direction. In thicker MEH-PPV or the blue-emitting cells, the doping did not reach the top of the CP layer. This led to broadened emitting junctions and/or unexpected junction locations. The bilayer LECs offer unique opportunities to investigate the ion transport in pristine CPs, the CP/SPE interface, and the SPE using highly sensitive and reliable imaging techniques. Removing the inert electrolyte polymer from the semiconducting CP can potentially lead to high-performance electrochemical light-emitting/photovoltaic cells or transistors.
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Affiliation(s)
- Kiran Birdee
- Department of Physics, Engineering Physics and Astronomy, Queen's University, Kingston, Ontario K7L 3N6, Canada
| | - Shiyu Hu
- Department of Physics, Engineering Physics and Astronomy, Queen's University, Kingston, Ontario K7L 3N6, Canada
| | - Jun Gao
- Department of Physics, Engineering Physics and Astronomy, Queen's University, Kingston, Ontario K7L 3N6, Canada
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Kawecki M, Hany R, Diethelm M, Jenatsch S, Grossmann Q, Bernard L, Hug HJ. Direct Measurement of Ion Redistribution and Resulting Modification of Chemical Equilibria in Polymer Thin Film Light-Emitting Electrochemical Cells. ACS APPLIED MATERIALS & INTERFACES 2018; 10:39100-39106. [PMID: 30335938 DOI: 10.1021/acsami.8b14198] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
The redistribution of ions in light-emitting electrochemical cells (LECs) plays a key role in their functionality. The direct quantitative mapping of ion density distributions in operating realistic sandwich-type devices, however, has not been experimentally achieved. Here we operate high-performing [Super Yellow/trimethylolpropane ethoxylate/lithium trifluoromethanesulfonate (Li+CF3SO3-)] LEC devices inside a time-of-flight secondary ion mass spectrometer and cool the devices after different operation times to liquid nitrogen temperatures before depth profiling is performed. The results reveal the dependence of the elemental and molecular distributions across the device layer on operation conditions. We find that the ion displacements lead to a substantial shift of the local chemical equilibria governing the free ion concentration.
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Affiliation(s)
- Maciej Kawecki
- Empa, Swiss Federal Laboratories for Materials Science and Technology , CH-8600 Dübendorf , Switzerland
- Department of Physics , University of Basel , CH-4056 Basel , Switzerland
| | - Roland Hany
- Empa, Swiss Federal Laboratories for Materials Science and Technology , CH-8600 Dübendorf , Switzerland
| | - Matthias Diethelm
- Empa, Swiss Federal Laboratories for Materials Science and Technology , CH-8600 Dübendorf , Switzerland
| | - Sandra Jenatsch
- Empa, Swiss Federal Laboratories for Materials Science and Technology , CH-8600 Dübendorf , Switzerland
| | - Quirin Grossmann
- Empa, Swiss Federal Laboratories for Materials Science and Technology , CH-8600 Dübendorf , Switzerland
| | - Laetitia Bernard
- Empa, Swiss Federal Laboratories for Materials Science and Technology , CH-8600 Dübendorf , Switzerland
| | - Hans J Hug
- Empa, Swiss Federal Laboratories for Materials Science and Technology , CH-8600 Dübendorf , Switzerland
- Department of Physics , University of Basel , CH-4056 Basel , Switzerland
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Moore MD, Bowler MH, Reynolds JE, Lynch VM, Shen Y, Slinker JD, Sessler JL. Ionic Organic Small Molecules as Hosts for Light-Emitting Electrochemical Cells. ACS APPLIED MATERIALS & INTERFACES 2018; 10:24699-24707. [PMID: 29952560 DOI: 10.1021/acsami.8b08176] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Light-emitting electrochemical cells (LEECs) from ionic transition-metal complexes (iTMCs) offer the potential for high-efficiency electroluminescence in a simple, single-layer device. However, LEECs typically rely on the use of rare metal complexes. This has limited their cost effectiveness and put constraints on their applicability. With a view to leveraging the efficient emission of these complexes while mitigating costs, we describe here a host/guest LEEC strategy that relies on the use of carbazole (Cz)-based organic small-molecule hosts and iTMC guests. Three cationic host molecules were prepared via the coupling of 1-(4-bromophenyl)-2-phenylbenzimidazole (PBI-Br) with Cz. This has allowed a comparison between the hosts bearing methoxy (PBI-CzOMe) and tert-butyl (PBI-Cz tBu) substituents, as well as an unsubstituted analogue (PBI-CzH). Cyclic voltammetry and UV-visible absorption revealed that all three host materials have wide band gaps characterized by reversible oxidation and irreversible reduction events. On the basis of electronic structure calculations, the host highest occupied molecular orbital (HOMO) resides primarily on the Cz moiety, whereas the lowest unoccupied molecular orbital (LUMO) is located primarily on the phenyl-benzimidazolium unit. Photoluminescence analysis of thin-film blends of PBI-CzH with iTMC guests confirmed that the emission was blue-shifted relative to pristine iTMC films, which is consistent with what was seen in dilute dichloromethane solution. LEEC devices were prepared based on thin films of the pristine hosts, pristine guests, and 90%/10% (w/w) host/guest blends. Among these host/guest blends, LEECs based on PBI-CzH displayed the best performance, particularly when an iridium complex was used as the guest. The system in question yielded a luminance maximum of 624 cd/m2 at an external quantum efficiency of 3.80%. This result stands in contrast to what is seen with typical organic light-emitting diode host studies, where tert-butyl substitution of the host generally leads to a better performance. To rationalize the present observations, the host materials were subject to single-crystal X-ray diffraction analysis. The resulting structures revealed clear head-to-tail interactions in the case of both PBI-CzH and PBI-CzOMe. No such interactions were evident in the case of PBI-Cz tBu. Furthermore, PBI-CzH showed a relatively smaller spacing between the successive HOMO and successive LUMO levels relative to PBI-CzOMe and PBI-Cz tBu, a finding consistent with more favorable charge transport and energy transfer. The results presented here can help inform the design and preparation of host materials suitable for use in single-layer iTMC LEECs.
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Affiliation(s)
- Matthew D Moore
- Department of Chemistry , The University of Texas at Austin , 105 East 24th Street , Austin , Texas 78712-1224 , United States
| | - Melanie H Bowler
- Department of Physics , The University of Texas at Dallas , 800 West Campbell Road , PHY 36, Richardson , Texas 75080-3021 , United States
| | - Joseph E Reynolds
- Department of Chemistry , The University of Texas at Austin , 105 East 24th Street , Austin , Texas 78712-1224 , United States
| | - Vincent M Lynch
- Department of Chemistry , The University of Texas at Austin , 105 East 24th Street , Austin , Texas 78712-1224 , United States
| | - Yulong Shen
- Department of Physics , The University of Texas at Dallas , 800 West Campbell Road , PHY 36, Richardson , Texas 75080-3021 , United States
| | - Jason D Slinker
- Department of Physics , The University of Texas at Dallas , 800 West Campbell Road , PHY 36, Richardson , Texas 75080-3021 , United States
| | - Jonathan L Sessler
- Department of Chemistry , The University of Texas at Austin , 105 East 24th Street , Austin , Texas 78712-1224 , United States
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7
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Bastatas LD, Moore MD, Slinker JD. The Effect of the Dielectric Constant and Ion Mobility in Light-Emitting Electrochemical Cells. Chempluschem 2017; 83:266-273. [DOI: 10.1002/cplu.201700500] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2017] [Indexed: 11/08/2022]
Affiliation(s)
- Lyndon D. Bastatas
- Department of Physics; The University of Texas at Dallas; 800 West Campbell Road, PHY 36 Richardson TX 75080-3021 USA
| | - Matthew D. Moore
- Department of Chemistry; The University of Texas at Austin; 105 East 24th Street Austin TX 78712 USA
| | - Jason D. Slinker
- Department of Physics; The University of Texas at Dallas; 800 West Campbell Road, PHY 36 Richardson TX 75080-3021 USA
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8
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AlTal F, Gao J. High resolution scanning optical imaging of a frozen planar polymer light-emitting electrochemical cell: an experimental and modelling study. Sci China Chem 2017. [DOI: 10.1007/s11426-016-9005-1] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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9
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Jafari MJ, Liu J, Engquist I, Ederth T. Time-Resolved Chemical Mapping in Light-Emitting Electrochemical Cells. ACS APPLIED MATERIALS & INTERFACES 2017; 9:2747-2757. [PMID: 28032741 DOI: 10.1021/acsami.6b14162] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
An understanding of the doping and ion distributions in light-emitting electrochemical cells (LECs) is required to approach a realistic conduction model which can precisely explain the electrochemical reactions, p-n junction formation, and ion dynamics in the active layer and to provide relevant information about LECs for systematic improvement of function and manufacture. Here, Fourier-transform infrared (FTIR) microscopy is used to monitor anion density profile and polymer structure in situ and for time-resolved mapping of electrochemical doping in an LEC under bias. The results are in very good agreement with the electrochemical doping model with respect to ion redistribution and formation of a dynamic p-n junction in the active layer. We also physically slow ions by decreasing the working temperature and study frozen-junction formation and immobilization of ions in a fixed-junction LEC device by FTIR imaging. The obtained results show irreversibility of the ion redistribution and polymer doping in a fixed-junction device. In addition, we demonstrate that infrared microscopy is a useful tool for in situ characterization of electroactive organic materials.
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Affiliation(s)
- Mohammad Javad Jafari
- Division of Molecular Physics, Department of Physics, Chemistry and Biology, Linköping University , Linköping SE-581 83, Sweden
| | - Jiang Liu
- Department of Science and Technology, Campus Norrköping, Linköping University , Norrköping SE-601 74, Sweden
| | - Isak Engquist
- Department of Science and Technology, Campus Norrköping, Linköping University , Norrköping SE-601 74, Sweden
| | - Thomas Ederth
- Division of Molecular Physics, Department of Physics, Chemistry and Biology, Linköping University , Linköping SE-581 83, Sweden
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10
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Lin KY, Bastatas LD, Suhr KJ, Moore MD, Holliday BJ, Minary-Jolandan M, Slinker JD. Influence of Lithium Additives in Small Molecule Light-Emitting Electrochemical Cells. ACS APPLIED MATERIALS & INTERFACES 2016; 8:16776-16782. [PMID: 27299981 DOI: 10.1021/acsami.6b03458] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Light-emitting electrochemical cells (LEECs) utilizing small molecule emitters such as iridium complexes have great potential as low-cost emissive devices. In these devices, ions rearrange during operation to facilitate carrier injection, bringing about efficient operation from simple, single layer devices. Recent work has shown that the luminance, efficiency, and responsiveness of iridium-based LEECs are greatly enhanced by the inclusion of small amounts of lithium salts (≤0.5%/wt) into the active layer. However, the origin of this enhancement has yet to be demonstrated experimentally. Furthermore, although iridium-based devices have been the longstanding leader among small molecule LEECs, fundamental understanding of the ionic distribution in these devices under operation is lacking. Herein, we use scanning Kelvin probe microscopy to measure the in situ potential profiles and electric field distributions of planar iridium-based LEECs and clarify the role of ionic lithium additives. In pristine devices, it is found that ions do not pack densely at the cathode, and ionic redistribution is slow. Inclusion of small amounts of Li[PF6] greatly increases ionic space charge near the cathode that doubles the peak electric fields and enhances electronic injection relative to pristine devices. This study confirms and clarifies a number of longstanding hypotheses regarding iridium LEECs and recent postulates concerning optimization of their operation.
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Affiliation(s)
- Kuo-Yao Lin
- Department of Physics, The University of Texas at Dallas , 800 West Campbell Road, PHY 36, Richardson, Texas 75080-3020, United States
| | - Lyndon D Bastatas
- Department of Physics, The University of Texas at Dallas , 800 West Campbell Road, PHY 36, Richardson, Texas 75080-3020, United States
| | - Kristin J Suhr
- Department of Chemistry, The University of Texas at Austin , 105 East 24th Street, Stop A5300, Austin, Texas 78712-0165, United States
| | - Matthew D Moore
- Department of Chemistry, The University of Texas at Austin , 105 East 24th Street, Stop A5300, Austin, Texas 78712-0165, United States
| | - Bradley J Holliday
- Department of Chemistry, The University of Texas at Austin , 105 East 24th Street, Stop A5300, Austin, Texas 78712-0165, United States
| | - Majid Minary-Jolandan
- Department of Mechanical Engineering, The University of Texas at Dallas , 800 West Campbell Road, EC 38, Richardson, Texas 75080-3020, United States
- Alan G. MacDiarmid NanoTech Institute, The University of Texas at Dallas , 800 West Campbell Road, Richardson, Texas 75080-3020, United States
| | - Jason D Slinker
- Department of Physics, The University of Texas at Dallas , 800 West Campbell Road, PHY 36, Richardson, Texas 75080-3020, United States
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Shoji TD, Zhu Z, Leger JM. Characterizing ion profiles in dynamic junction light-emitting electrochemical cells. ACS APPLIED MATERIALS & INTERFACES 2013; 5:11509-11514. [PMID: 24175736 DOI: 10.1021/am403805j] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Organic semiconductors have the unique ability to conduct both ionic and electronic charge carriers in thin films, an emerging advantage in applications such as light-emitting devices, transistors, and electrochromic devices, among others. Evidence suggests that the profiles of ions and electrochemical doping in the polymer film during operation significantly impact the performance and stability of the device. However, few studies have directly characterized ion profiles within LECs. Here, we present an in-depth study of the profiles of ion distributions in LECs following application of voltage, via time-of-flight secondary ion mass spectrometry. Ion distributions were characterized with regard to film thickness, salt concentration, applied voltage, and relaxation over time. Results provide insight into the correlation between ion profiles and device performance, as well as potential approaches to tuning the electrochemical doping processes in LECs.
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Affiliation(s)
- Tyko D Shoji
- Department of Physics and Astronomy, Western Washington University , Bellingham, Washington 98225-9164, United States
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12
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Tang S, Sandström A, Fang J, Edman L. A Solution-Processed Trilayer Electrochemical Device: Localizing the Light Emission for Optimized Performance. J Am Chem Soc 2012; 134:14050-5. [DOI: 10.1021/ja3041916] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Shi Tang
- The Organic Photonics and Electronics
Group, Umeå University, SE-901 87
Umeå, Sweden
| | - Andreas Sandström
- The Organic Photonics and Electronics
Group, Umeå University, SE-901 87
Umeå, Sweden
| | - Junfeng Fang
- Ningbo
Institute of Materials
Technology and Engineering, Chinese Academy of Sciences, Ningbo, 315211 Zhejiang, People’s Republic of China
| | - Ludvig Edman
- The Organic Photonics and Electronics
Group, Umeå University, SE-901 87
Umeå, Sweden
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