| 1. |
- Adranno, Brando, et al.
(författare)
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Broadband white-light-emitting electrochemical cells
- 2023
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Ingår i: Advanced Photonics Research. - : John Wiley & Sons. - 2699-9293. ; 4:5
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Tidskriftsartikel (refereegranskat)abstract
- Emerging organic light-emitting devices, such as light-emitting electrochemical cells (LECs), offer a multitude of advantages but currently suffer from that most efficient phosphorescent emitters are based on expensive and rare metals. Herein, it is demonstrated that a rare metal-free salt, bis(benzyltriphenylphosphonium)tetrabromidomanganate(II) ([Ph3PBn]2[MnBr4]), can function as the phosphorescent emitter in an LEC, and that a careful device design results in the fact that such a rare metal-free phosphorescent LEC delivers broadband white emission with a high color rendering index (CRI) of 89. It is further shown that broadband emission is effectuated by an electric-field-driven structural transformation of the original green-light emitter structure into a red-emitting structure.
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| 2. |
- Adranno, Brando, et al.
(författare)
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The 8-hydroxyquinolinium cation as a lead structure for efficient color-tunable ionic small molecule emitting materials
- 2023
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Ingår i: Advanced Photonics Research. - : John Wiley & Sons. - 2699-9293. ; 4:3
-
Tidskriftsartikel (refereegranskat)abstract
- Albeit tris(8-hydroxyquinolinato) aluminum (Alq3) and its derivatives are prominent emitter materials for organic lighting devices, and the optical transitions occur among ligand-centered states, the use of metal-free 8-hydroxyquinoline is impractical as it suffers from strong nonradiative quenching, mainly through fast proton transfer. Herein, it is shown that the problem of rapid proton exchange and vibration quenching of light emission can be overcome not only by complexation, but also by organization of the 8-hydroxyquinolinium cations into a solid rigid network with appropriate counter-anions (here bis(trifluoromethanesulfonyl)imide). The resulting structure is stiffened by secondary bonding interactions such as pi-stacking and hydrogen bonds, which efficiently block rapid proton transfer quenching and reduce vibrational deactivation. Additionally, the optical properties are tuned through methyl substitution from deep blue (455 nm) to blue-green (488 nm). Time-dependent density functional theory (TDFT) calculations reveal the emission to occur from which an unexpectedly long-lived S-1 level, unusual for organic fluorophores. All compounds show comparable, even superior photoluminescence compared to Alq3 and related materials, both as solids and thin films with quantum yields (QYs) up to 40-50%. In addition, all compounds show appreciable thermal stability with decomposition temperatures above 310 °C.
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| 3. |
- Auroux, Etienne, et al.
(författare)
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A metal-free and transparent light-emitting device by sequential spray-coating fabrication of all layers including PEDOT:PSS for both electrodes
- 2023
-
Ingår i: RSC Advances. - : Royal Society of Chemistry. - 2046-2069. ; 13:25, s. 16943-16951
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 4. |
- Auroux, Etienne, et al.
(författare)
-
Evidence and Effects of Ion Transfer at Active-Material/Electrode Interfaces in Solution-Fabricated Light-Emitting Electrochemical Cells
- 2021
-
Ingår i: Advanced Electronic Materials. - : Wiley-Blackwell Publishing Inc.. - 2199-160X. ; 7:8
-
Tidskriftsartikel (refereegranskat)abstract
- The light-emitting electrochemical cell (LEC) allows for energy- and cost-efficient printing and coating fabrication of its entire device structure, including both electrodes and the single-layer active material. This attractive fabrication opportunity is enabled by the electrochemical action of mobile ions in the active material. However, a related and up to now overlooked issue is that such solution-fabricated LECs commonly comprise electrode/active-material interfaces that are open for transfer of the mobile ions, and it is herein demonstrated that a majority of the mobile anions in a common spray-coated active material can transfer into a spray-coated poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) positive electrode during LEC operation. Since it is well established that the mobile ion concentration in the active material has a profound influence on the LEC performance, this significant ion transfer is an important factor that should be considered in the design of low-cost LEC devices that deliver high performance.
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| 5. |
- Auroux, Etienne, et al.
(författare)
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Ion transfer into solution-processed electrodes can significantly shift the p-n junction and emission efficiency of light-emitting electrochemical cells
- 2022
-
Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 121:23
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 6. |
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| 7. |
- Auroux, Etienne, et al.
(författare)
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Solution -based fabrication of the top electrode in light -emitting electrochemical cells
- 2020
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Ingår i: Organic electronics. - : Elsevier. - 1566-1199 .- 1878-5530. ; 84
-
Tidskriftsartikel (refereegranskat)abstract
- The light-emitting electrochemical cell (LEC) has demonstrated capacity for cost- and material-efficient solution-based fabrication of the active material under ambient air. In this context, it is notable that corresponding reports on a scalable solution-based fabrication of the electrodes, particularly the top electrode, are rare. We address this issue through the demonstration of a transparent LEC, which is fabricated under ambient air by sequential spray deposition of a hydrophobic conjugated-polymer:ionic-liquid blend ink as the active material and a hydrophilic poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) ink as the transparent top electrode. Such an optimized LEC delivers a luminance of 360 cd/m2 at a power efficacy of 1.6 lm/W, which is on par with the performance of a corresponding LEC device equipped with a vacuum-deposited and reflective metal top electrode. This implies that the entire LEC device indeed can be fabricated with solution-based processes and deliver a good performance, which is critical if the LEC technology is going to fulfil its low-cost potential.
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| 8. |
- Auroux, Etienne, 1993-
(författare)
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Solution-processed light-emitting electrochemical cells : challenges and opportunities
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Our world is filling up with electronics. High-tech gadgets are integrated everywhere, from smart fridges able to track expiry dates and food usage, to microchip implants that let us unlock doors and pay with our hands. As innovative as they are, these new products and the many more to come impose new requirements on materials and fabrication methods. For instance, emerging electronic technologies that deliver light emission such as smart labels, authenticity features and light-based medical therapies, are often required to be flexible, see-through and low-cost, and in addition sustainable to fabricate, operate and recycle.In response to these challenges, the light-emitting industry is turning to organic electronics for solutions, a field that promises resource-efficient fabrication using environmentally benign materials. An interesting proposal is that of the light-emitting electrochemical cell (LEC), which, thanks to its simple structure, is well suitedfor high-throughput fabrication. The LEC is in many aspects a smart device, able to reorganize itself during operation via the electrochemical action of mobile ions, which create the injection and transport layers that require additional fabrication steps in other technologies. This elegant behavior makes the LEC tolerant to a large array of materials and fabrication methods, and hence a good fit for many applications.Yet the LEC is still today a scientific curiosity rather than an actual commercial solution and among the very few prototypes available on the market, none are able to meet the combined performance, resource efficiency and sustainability criteria. As a matter of fact, of the three layers that make an LEC, i.e., two electrodes surrounding an active material, only the later meet these requirements thanks to a strong recent research effort. In comparison, the electrodes have received little attention and are almost exclusively comprising metals or metal oxides deposited by time- and energy-expensive fabrication methods, making the LEC as a whole unfit for many applications.In an effort to push the LEC toward the untapped commercial niche of low-cost lighting, we tackle the problem of electrode fabrication with resource-efficiency in mind. We first show that up-scalable spray coating of inks under ambient air is a viable mean of fabrication for both active materials and electrodes alike. However, in doing so, we find that we create electrode interfaces that are open to ion transfer; an up-to-now overlooked issue that needs careful consideration when designing solution-processed LECs. Building on our discovery, we demonstrate that it is possible to fabricate an LEC entirely by using spray coating metal-free and organic inks; thereby demonstrating that an all-organic, metal-free and resource-efficient LEC is possible.I hope that our efforts will encourage others to work on solution-processed LECs, electrodes included, and develop ready-to-use products.
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| 9. |
- Barzegar, Hamid Reza, et al.
(författare)
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Self-assembled PCBM nanosheets : a facile route to electronic layer-on-Layer heterostructures
- 2018
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Ingår i: Nano letters (Print). - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 18:2, s. 1442-1447
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Tidskriftsartikel (refereegranskat)abstract
- We report on the self-assembly of semicrystalline [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) nanosheets at the interface between a hydrophobic solvent and water, and utilize this opportunity for the realization of electronically active organic/organic molecular heterostructures. The self-assembled PCBM nanosheets can feature a lateral size of >1 cm2 and be transferred from the water surface to both hydrophobic and hydrophilic surfaces using facile transfer techniques. We employ a transferred single PCBM nanosheet as the active material in a field-effect transistor (FET) and verify semiconductor function by a measured electron mobility of 1.2 × 10–2 cm2 V–1 s–1 and an on–off ratio of ∼1 × 104. We further fabricate a planar organic/organic heterostructure with the p-type organic semiconductor poly(3-hexylthiophene-2,5-diyl) as the bottom layer and the n-type PCBM nanosheet as the top layer and demonstrate ambipolar FET operation with an electron mobility of 8.7 × 10–4 cm2 V–1 s–1 and a hole mobility of 3.1 × 10–4 cm2V–1 s–1.
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| 10. |
- Bychkov, Vitaly, 1968-, et al.
(författare)
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Speedup of doping fronts in organic semiconductors through plasma instability
- 2011
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 107:1, s. 016103-016107
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Tidskriftsartikel (refereegranskat)abstract
- The dynamics of doping transformation fronts in organic semiconductor plasma is studied for application in light-emitting electrochemical cells. We show that new fundamental effects of the plasma dynamics can significantly improve the device performance. We obtain an electrodynamic instability, which distorts the doping fronts and increases the transformation rate considerably. We explain the physical mechanism of the instability, develop theory, provide experimental evidence, perform numerical simulations, and demonstrate how the instability strength may be amplified technologically. The electrodynamic plasma instability obtained also shows interesting similarity to the hydrodynamic Darrieus-Landau instability in combustion, laser ablation, and astrophysics.
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| 11. |
- Doeff, Marca M., et al.
(författare)
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A high-rate manganese oxide for rechargeable lithium battery applications
- 2001
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Ingår i: Journal of the Electrochemical Society. - : Electrochemical Society Inc. - 0013-4651 .- 1945-7111. ; 148:3, s. A230-A236
-
Tidskriftsartikel (refereegranskat)abstract
- LixMnO2 made by ion exchange of glycine-nitrate combustion synthesis-processed (GNP) orthorhombic Na0.44MnO2 (GNP-LixMnO2) has been cycled in lithium/liquid electrolyte cell configurations at room temperature and lithium/polymer cell configurations at 85 degreesC over one hundred times without showing capacity fading or phase conversion to spinel. At 2.5 mA/cm2 in liquid cells (5C rate) or 1 mA/cm2 (1.5C rate) in polymer cells, 80-95% of the expected capacity is delivered. The remarkable stability is attributable to the unusual double tunnel structure, which cannot easily undergo rearrangement to spinel. The enhanced rate capability of GNP-LixMnO2 compared to conventionally prepared materials is attributable to the shorter particle length, which allows faster diffusion of lithium ions along the tunnels.
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| 12. |
- Doeff, M.M, et al.
(författare)
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Transport properties of binary salt polymer electrolytes
- 2000
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Ingår i: Journal of Power Sources. - : Elsevier. - 0378-7753 .- 1873-2755. ; 89:2, s. 227-231
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Tidskriftsartikel (refereegranskat)abstract
- Transport properties (ionic conductivities (σ), salt diffusion coefficients (Ds), and cationic transference numbers (t+0)) as a function of salt concentration (Cs) are reported and compared for several common binary salt/polymer systems being considered for use as electrolytes in rechargeable lithium batteries for electric vehicle and other applications. The three properties provide a complete description of transport in solid polymer electrolytes (SPEs) or "dry" systems in cells undergoing galvanostatic charge and discharge. The macroscopic approach used obviates the need to know the details of speciation in these non-ideal solutions and allows for a more sophisticated correlation of the characteristics of ion transport with polymer structure, salt type, and concentration than conductivity data alone.
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| 13. |
- dos Santos, John Marques, et al.
(författare)
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Color tuning of multi-resonant thermally activated delayed fluorescence emitters based on fully fused polycyclic amine/carbonyl frameworks
- 2023
-
Ingår i: Journal of Materials Chemistry C. - : Royal Society of Chemistry. - 2050-7526 .- 2050-7534. ; 11:24, s. 8263-8273
-
Tidskriftsartikel (refereegranskat)abstract
- Two novel π-extended amine/carbonyl-based multi-resonance thermally activated delayed fluorescence (MR-TADF) emitters have been designed and synthesized. The two emitters are isomeric, composed of nine fused rings and show green-yellow emission. Sym-DiDiKTa and Asym-DiDiKTa possess tert-butyl groups distributed in a symmetrical and asymmetrical fashion, respectively, which significantly impact the single-crystal packing structure. The two compounds possess similar singlet-triplet energy gaps, ΔEST, of around 0.23 eV, narrowband emission characterized by a full-width at half-maximum, FWHM, of 29 nm and a photoluminescence quantum yield, ΦPL, of 70% and 53% for the symmetric and asymmetric counterparts, respectively, in toluene. Investigation in OLEDs demonstrated that the devices with Sym-DiDiKTa and Asym-DiDiKTa displayed electroluminescence maxima of 543 and 544 nm, and maximum external quantum efficiencies (EQEmax) of 9.8% and 10.5%, respectively. The maximum EQE was further improved to 19.9% by employing a hyperfluorescence strategy. We further present the first example of a neutral MR-TADF emitter incorporated in a LEC device where Sym-DiDiKTa acts as the emitter. The LEC shows a λEL at 551 nm and FWHM of 60 nm with luminance of 300 cd m−2 and a fast turn-on time of less than 2 s to 100 cd m−2
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| 14. |
- Edman, Ludvig, 1967-, et al.
(författare)
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Effect of C60 as a Filler on the Morphology of Polymer−Salt Complexes Based on Poly(ethylene oxide) and LiCF3SO3
- 1999
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 32:12, s. 4130-4133
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Tidskriftsartikel (refereegranskat)abstract
- The inclusion of C60 as a filler in complexes of paly(ethylene oxide) (PEO) and LiCF3SO3 salt reduces the degree of crystallinity of the material at ambient temperature. The observed effects are manifested as changes in characteristic vibrational modes of the crystalline polymer in FT-Raman spectra over a range of temperatures. The introduction of relatively small amounts of C60 also stabilizes ionic substructures present in these systems. Interestingly, no internal modes of the C60 molecule are affected by dissolution in PEO or by the presence of varying amounts of LiCF3SO3 salt in the matrix. From the absence of a shift in the C60:s charge-transfer-sensitive Ag(2) mode, in particular, it appears as though C60 essentially acts as an inert filler in these complexes.
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| 15. |
- Edman, Ludvig, 1967-, et al.
(författare)
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Influence of the anion on the kinetics and stability of a light-emitting electrochemical cell
- 2003
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Ingår i: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 138:3, s. 441-446
-
Tidskriftsartikel (refereegranskat)abstract
- The selection of the anion is shown to be crucial for the response time and the lifetime of light-emitting electrochemical cells (LECs) fabricated with [co-block phenyl-substituted poly(para phenylene vinylene)]-PEO-LiX (X = Tf, TFSI, Tf-TFSI). With a mixed-anion (X = Tf-TFSI) salt. the LEC turned on in less than 0.4 s at ΔU = 4.0 V, with X = TFS1 it turned on in a few seconds, while X = Tf produced devices with significantly larger response times with a strong dependence on the film thickness. We attribute this significant variation in the response to the morphology of the PEO-LiX phase at room temperature: PEO-LiTf is largely crystalline with a correspondingly limited ionic mobility: PEO-LiTf-TFSI is amorphous with a relatively high mobility; and heat-treated PEO-LiTFSI is typically partially amorphous. For lifetimes. we focused on 3.0 ≤ ΔU ≤ 4.0 V since this range coincided with a crossover in performance for the X = Tf devices. At ΔU = 3.0 V, these lasted the entire measurement cycle (=55 h) with constant efficiency and only a small decrease in light output. At ΔU ≥ 3.25 V. the same devices exhibited a limited lifetime with a linear dependence on the salt concentration and a decrease in the efficiency with time. For X = TFSI. Tf-TFSI short lifetimes and a decrease in efficiency with time were obtained independent of the applied voltage. Considering recently published data on electrochemical stability, we propose that an irreversible overreduction of the anion is a significant side reaction that limits the lifetime of LEC systems.
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| 16. |
- Edman, Ludvig, 1967-
(författare)
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Ion Association and Ion Solvation Effects at the Crystalline−Amorphous Phase Transition in PEO−LiTFSI
- 2000
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 104:31, s. 7254-7258
-
Tidskriftsartikel (refereegranskat)abstract
- From band shape analyses of the strong 740 cm-1 Raman mode of the TFSI anion, we deduce that the crystalline state of the P(EO)nLiTFSI system contains a very small amount of ion pairs (approximate to 7%), most probably belonging to the minor amorphous phase, for the n greater than or equal to 6 range. For all-amorphous samples, we found a small amount of ion pairs for n greater than or equal to 8, but a significant amount (approximate to 24%) for n = 6. This increase in ion pair formation coincides with a decrease in the relative solvation of lithium cations by polymeric ether oxygens, as detected from a careful study of the 863 cm-1 polymer-cation "breathing mode". We therefore propose that the local ionic structure is preserved during the melting of n greater than or equal to 8 compositions, but that there is a changeover from a predominately ether oxygen lithium coordination to a combined ether oxygen and anionic coordination of the lithium cations for more concentrated samples upon melting.
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| 17. |
- Edman, Ludvig, 1967-, et al.
(författare)
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Single-component light-emitting electrochemical cell with improved stability
- 2003
-
Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 82:22, s. 3961-3963
-
Tidskriftsartikel (refereegranskat)abstract
- We report a single-component polymeric light-emitting electrochemical cell with poly[9,9'-bis[6"-(N, N, N-trimethylammonium)hexyl]fluorene-alt-co-phenylene]bromide (PFN+Br-) as the active material. Indium tin oxide/PFN+Br-/aluminum sandwich structures demonstrate a low and thickness-independent turn-on voltage (2.9 V) for blue light emission. Thermophysical characterization shows that PFN+Br- is in a metastable amorphous phase after spin casting, but that crystallization takes place at elevated temperatures. With this information at hand, we allowed devices to turn-on via ionic redistribution (and the formation of a p-i-n junction) in the amorphous phase, and then stabilized this desired configuration through crystallization. We find significantly improved lifetimes and relatively fast turn-on times for these single-component devices operating at room temperature.
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| 18. |
- Edman, Ludvig, 1967-, et al.
(författare)
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Slow recrystallization in the polymer electrolyte system poly(ethylene oxide)n–LiN(CF3SO2)2
- 2000
-
Ingår i: Journal of Materials Research. - : Materials Research Society. - 0884-2914 .- 2044-5326. ; 15:9, s. 1950-1954
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Tidskriftsartikel (refereegranskat)abstract
- Thermal and ion-transport properties of the salt-in-polymer system poly(ethylene oxide)n-LiN(CF3SO2)2 [P(EO)nLiTFSI] were investigated for compositions ranging from n =5 to n = 50. Particular attention was paid to the region n = 8 to 10 where a crystallinity gap previously had been reported. We concluded that the absence of distinct melting transitions for salt-rich compositions (n = 5 to 12) was attributable to the extremely slow kinetics of recrystallization of this system following a heat treatment. The results further indicated that it was primarily the nucleation process that was inhibited by the [(bis)trifluoromethanesulfonate imide] (TFSI) anion. As a corollary, the ionic conductivity was strongly dependent on the thermal history of samples, and an enhancement of up to 300% was observed in the ambient temperature ionic conductivity for pre-heated salt-rich samples.
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| 19. |
- Edman, Ludvig, 1967-, et al.
(författare)
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Thermal analysis of a solid polymer electrolyte and a subsequent electrochemical investigation of a lithium polymer battery
- 2003
-
Ingår i: Solid State Ionics. - : Elsevier. - 0167-2738 .- 1872-7689. ; 158:1-2, s. 177-186
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Tidskriftsartikel (refereegranskat)abstract
- A notable slow recrystallization process following heating above the liquidus line for P(EO)nLiTFSI electrolytes with n values ranging from 5 to 12 is shown to be correlated to a slow nucleation process as concluded from extensive differential scanning calorimetry (DSC) measurements. This concentration anomaly motivated the assembly of a room temperature Li/P(EO)8LiTFSI/LixMnO2 cell, containing a preheated amorphous electrolyte, which initially delivered a cathode capacity of 27 mAh/g at a current density of 0.1 mA/cm2 and 60 mAh/g at 0.05 mA/cm2 as compared to typical discharge capacities of 95 - 120 mAh/g for similar polymer systems at 85 degreesC and liquid systems at room temperature. The delivered capacity decreased during cell cycling and reached a limiting value of 10 mAh/g after cycle 15. Li/P(EO)nLiTFSl/LixMnO2 cells (n = 6, 8, 20) were also cycled extensively at 85 degreesC, and an analysis of the results indicates that the solid electrolyte interfacial (SEI) resistance, formed between the lithium negative electrode and the electrolyte, remains constant during cycling (RSEI ≈ 3-7 x 10-3 Ωm2) and is of the same magnitude as the bulk electrolyte resistance. Furthermore, it is shown that severe concentration gradients develop over the electrolytes during cell operation, and that the marked diminishing cathode capacity for the n = 8 cell at 20 degreesC, and also for the n = 20 cell at 85 degreesC, with increasing current density, appears to be related to a limiting current situation. Losses in energy and power densities at steady state conditions for n = 6 and n = 8 cells at 85 degreesC appear mainly related to the development of a concentration overpotential, which lowers the working potential curve and causes the cutoff potential to be reached sooner.
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| 20. |
- Edman, Ludvig, 1967-, et al.
(författare)
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Transport properties of the Solid polymer electrolyte system P(EO)nLiTFSI
- 2000
-
Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 104:15, s. 3476-3480
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Tidskriftsartikel (refereegranskat)abstract
- Values for the lithium ion transference number (t0+)) are reported for the solid polymer electrolyte system poly(ethylene oxide) (PEO) complexed with Li(CF3SO2)2N (LiTFSI). t0+,ranges from 0.17 ± 0.17 to 0.60 ± 0.03 in the salt concentration (c) region of 742 to 2982 mol/m3 at 85 degrees C. The concentration dependence of t0+ and the molar ionic conductivity (Λ) are shown to be in good agreement with a free volume approach over the salt-rich composition range investigated. The present t0+ results were obtained using an electrochemical technique based on concentrated solution theory. This experimentally straightforward method is herein demonstrated to give accurate results for a highly concentrated SPE system, without relying on any dubious simplifications regarding the state of the electrolyte.
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| 21. |
- Ekeroth, Sebastian, 1988-, et al.
(författare)
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Catalytic nanotruss structures realized by magnetic self-assembly in pulsed plasma
- 2018
-
Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 18:5, s. 3132-3137
-
Tidskriftsartikel (refereegranskat)abstract
- Tunable nanostructures that feature a high surface area are firmly attached to a conducting substrate and can be fabricated efficiently over significant areas, which are of interest for a wide variety of applications in, for instance, energy storage and catalysis. We present a novel approach to fabricate Fe nanoparticles using a pulsed-plasma process and their subsequent guidance and self-organization into well-defined nanostructures on a substrate of choice by the use of an external magnetic field. A systematic analysis and study of the growth procedure demonstrate that nondesired nanoparticle agglomeration in the plasma phase is hindered by electrostatic repulsion, that a polydisperse nanoparticle distribution is a consequence of the magnetic collection, and that the formation of highly networked nanotruss structures is a direct result of the polydisperse nanoparticle distribution. The nanoparticles in the nanotruss are strongly connected, and their outer surfaces are covered with a 2 nm layer of iron oxide. A 10 μm thick nanotruss structure was grown on a lightweight, flexible and conducting carbon-paper substrate, which enabled the efficient production of H2 gas from water splitting at a low overpotential of 210 mV and at a current density of 10 mA/cm2.
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| 22. |
- Ekeroth, Sebastian, et al.
(författare)
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Magnetically Collected Platinum/Nickel Alloy Nanoparticles as Catalysts for Hydrogen Evolution
- 2021
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Ingår i: ACS Applied Nano Materials. - : American Chemical Society (ACS). - 2574-0970. ; 4:12, s. 12957-12965
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Tidskriftsartikel (refereegranskat)abstract
- The hydrogen evolution reaction (HER) is a key process in electrochemical water splitting. To lower the cost and environmental impact of this process, it is highly motivated to develop electrocatalysts with low or no content of noble metals. Here, we report on an ingenious synthesis of hybrid PtxNi1-x electrocatalysts in the form of a nanoparticle-nanonetwork structure with very low noble metal content. The structure possesses important features such as good electrical conductivity, high surface area, strong interlinking, and substrate adhesion, which render an excellent HER activity. Specifically, the best performing Pt0.05Ni0.95 sample demonstrates a Tafel slope of 30 mV dec-1 in 0.5 M H2SO4 and an overpotential of 20 mV at a current density of 10 mA cm-2 with high stability. The impressive catalytic performance is further rationalized in a theoretical study, which provides insight into the mechanism on how such small platinum content can allow for close-to-optimal adsorption energies for hydrogen.
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| 23. |
- Ekspong, Joakim, 1987-
(författare)
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Electrocatalysts for sustainable hydrogen energy : disordered and heterogeneous nanomaterials
- 2021
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- With the current global greenhouse gas emissions, our remaining carbon budget is depleted in only 7 years. After that, several biophysical systems are predicted to collapse such as the arctic ice, coral reefs and the permafrost, leading to potentially irreversible consequences. Our emissions are strongly correlated to access of energy and even if we are aware of the planetary emergency today, our emissions still continue to grow. Electrical vehicles have the possibility to reduce the emissions in the transportation sector significantly. However, these vehicles are still expensive and impractical for long-distance or heavy transportation. While political actions and technological development are essential to keep prices down, the driving dis- tance can be increased by replacing the batteries for onboard electricity production. In hydrogen fuel cells, electricity is produced by combining hydrogen gas (H2) and oxygen with only water as the by-product and if employed in electrical vehicles, distances of 500 km are enabled with a refueling time in 5 minutes. For other uses than in vehicles, H2 is also promising for large-scale electricity storage and for several industrial processes such as manufacturing CO2-free steel, ammonia and synthetic fuels. However, today most H2 production methods relies on fossil fuels and releases huge amounts of CO2. Electrolysis of water is an alternative production method where H2, along with oxygen are produced from water. To split the water, electricity has to be added and if renewable energy sources are used, the method has zero emissions and is considered most promising for a sustainable hydrogen energy economy. The tech- nique is relatively expensive compared to the fossil fuel-based methods and relies on rare noble metals such as platinum as catalysts for decreasing the required energy to split water. For large scale productions, these metals need to be replaced by more sustainable and abundant catalysts to lower the cost and minimize the environmental impacts. In this thesis we have investigated such candidates for the water splitting reaction but also to some extent for the oxygen reduction reaction in fuel cells. By combining theory and experiments we hope to aid in the development and facilitate a transition to clean hydrogen energy. We find among other things that i) defects in catalytic materials plays a significant role the performance and efficiency, and that ii) heterogeneity influence the adsorption energies of reaction intermediates and hence the catalytic efficiency and iii) while defects are not often studied for electrocatalytic reactions, these may inspire for novel materials in the future.
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| 24. |
- Ekspong, Joakim, et al.
(författare)
-
Solar-driven water splitting at 13.8 % solar-to-hydrogen efficiency by an earth-abundant PV-electrolyzer
- 2021
-
Ingår i: ACS Sustainable Chemistry and Engineering. - : American Chemical Society (ACS). - 2168-0485. ; 9:42, s. 14070-14078
-
Tidskriftsartikel (refereegranskat)abstract
- We present the synthesis and characterization of an efficient and low cost solar-driven electrolyzer consisting of Earth-abundant materials. The trimetallic NiFeMo electrocatalyst takes the shape of nanometer-sized flakes anchored to a fully carbon-based current collector comprising a nitrogen-doped carbon nanotube network, which in turn is grown on a carbon fiber paper support. This catalyst electrode contains solely Earth-abundant materials, and the carbon fiber support renders it effective despite a low metal content. Notably, a bifunctional catalyst–electrode pair exhibits a low total overpotential of 450 mV to drive a full water-splitting reaction at a current density of 10 mA cm–2 and a measured hydrogen Faradaic efficiency of ∼100%. We combine the catalyst–electrode pair with solution-processed perovskite solar cells to form a lightweight solar-driven water-splitting device with a high peak solar-to-fuel conversion efficiency of 13.8%.
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| 25. |
- Enevold, Jenny, 1981-
(författare)
-
Structure and morphology control of organic semiconductors for functional optoelectronic applications
- 2019
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The functionality and application of organic semiconductors are largely dependent on their constituent structure and morphology. This thesis presents a number of functional and novel approaches for the control and tuning of structural and morphological features of a variety of organic semiconductor materials, and also demonstrates that these approaches can be utilized for improved device operation of field-effect transistors, organic solar cells and light-emitting electrochemical cells.The fullerene family is a particular group of closed-cage organic semiconductors, which can be photochemically coupled into larger dimeric or polymeric structures through the excitation of the fullerene molecules by light emission. In Paper I, we perform a detailed experimental and analytical investigation, which demonstrates that this photochemical monomer-to-dimer transformation requires that both constituent fullerene molecules are photoexcited. The direct consequence is that the initial probability for the photochemical transformation is dependent on the square of the light-emission intensity.The photochemical coupling of fullerene molecules commonly results in a distinctly lowered solubility in common hydrophobic solvents, which can be utilized for the direct patterning of fullerene films by resist-free lithography. In Paper II, we utilize this patterning opportunity for the fabrication of one-dimensional fullerene nano-stripes using two-beam laser interference lithography. A desired high contrast between the patterned and non-patterned fullerene regions is facilitated by the non-linear response of the photochemical transformation process, as predicted by the findings in Paper I. The patterned fullerene nano-stripes were utilized as the active material in field-effect transistors, which featured high electron mobility and large on-off ratio.This patterning was in Paper III extended into easy tunable two-dimensional fullerene structures by the design and development of an exposure setup, essentially comprising a laser and a spatial light modulator featuring >8 millions of independently controlled mirrors. With this approach, we could fabricate well-defined fullerene microdots over a several square-millimeter sized area, which was utilized as an internal out-coupling layer in a light-emitting electrochemical cell with significantly enhanced light output.Paper IV reports on the development of a new “spray-sintering” method for the cost-efficient solution-based deposition of the active material in light-emitting electrochemical cells. This carefully designed approach effectively resolves the issue with phase separation between the hydrophobic organic semiconductor and the hydrophilic electrolyte that results in a sub-par LEC performance, and also allows for the direct fabrication of LEC devices onto complex surfaces, including a stainless-steel fork.Paper V finally reports on the design and synthesis of a soluble small molecule, featuring a donor-acceptor-donor configuration. It acts as the donor when combined with a soluble fullerene acceptor in the active material of organic solar cells, and such devices with optimized donor/acceptor nanomorphology feature a high open-circuit voltage of ~1.0 V during solar illumination.
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| 26. |
- Enevold, Jenny, et al.
(författare)
-
Tunable two-dimensional patterning of a semiconducting Nanometer-Thin C60 fullerene film using a spatial light modulator
- 2020
-
Ingår i: ACS Applied Nano Materials. - : Acoustical Society of America (ASA). - 2574-0970. ; 3:6, s. 2574-0970
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The photochemical coupling of fullerene molecules into covalently connected oligomeric or polymeric structures can result in drastically lowered solubility in common solvents with retained semiconductor properties. Here, we exploit this combination of properties for the utilization of fullerenes as a negative photoresist material with electronic functionality. Specifically, we develop an easily tunable exposure system, essentially comprising a laser and a computer-controlled spatial light modulator (SLM) featuring >8 million independently controlled pixels, for the spatially selective photochemical transformation of nanometer-thin C60 fullerene films. With a carefully designed laser-SLM-exposure/solvent-development cycle, we are able to realize well-resolved two-dimensional hexagonal or square patterns of circular C60 microdots with a center-to-center distance of 1–5 μm and a maximum thickness of 20–35 nm over several square-millimeter-sized areas on a substrate. The functionality of such a hexagonal C60 pattern was demonstrated by its inclusion in between the transparent electrode and the active material in a light-emitting electrochemical cell, which featured an enhanced light output by >50% in comparison to a reference device void of the patterned C60 layer.
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| 27. |
- Fang, Junfeng, et al.
(författare)
-
Identifying and Alleviating Electrochemical Side-Reactions in Light-Emitting Electrochemical Cells
- 2008
-
Ingår i: Journal of the American Chemical Society.. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 130:13, s. 4562-4568
-
Tidskriftsartikel (refereegranskat)abstract
- We demonstrate that electrochemical side-reactions involving the electrolyte can be a significant and undesired feature in light-emitting electrochemical cells (LECs). By direct optical probing of planar LECs, comprising Au electrodes and an active material mixture of {poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) + poly(ethylene oxide) (PEO) + KCF3SO3}, we show that two direct consequences of such a side-reaction are the appearance of a -degradation layer- at the negative cathode and the formation of the light-emitting p−n junction in close proximity to the cathode. We further demonstrate that a high initial drive voltage and a high ionic conductivity of the active material strongly alleviate the extent of the side reaction, as evidenced by the formation of a relatively centered p−n junction, and also rationalize our findings in the framework of a general electrochemical model. Finally, we show that the doping concentrations in the doped regions at the time of the p−n junction formation are independent of the applied voltage and relatively balanced at 0.11 dopants/MEH-PPV repeat unit in the p-type region and 0.15 dopants/MEH-PPV repeat unit in the n-type region.
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| 28. |
- Fang, Junfeng, et al.
(författare)
-
The design and realization of flexible light-emitting electrochemical cells with record-long lifetime
- 2009
-
Ingår i: Advanced Functional Materials. - : Wiley. - 1616-301X .- 1616-3028. ; 19:16, s. 2671-2676
-
Tidskriftsartikel (refereegranskat)abstract
- Polymer light-emitting electrochemical cells (LECs) offer an attractive opportunity for low-cost production of functional devices in flexible and large-area configurations, but the critical drawback in comparison to competing light-emission technologies is a limited operational lifetime. Here, it is demonstrated that it is possible to improve the lifetime by straightforward and motivated means from a typical value of a few hours to more than one month of uninterrupted operation at significant brightness (>100 cd m−2) and relatively high power conversion efficiency (2 lm W−1 for orange-red emission). Specifically, by optimizing the composition of the active material and by employing an appropriate operational protocol, a desired doping structure is designed and detrimental chemical and electrochemical side reactions are identified and minimized. Moreover, the first functional flexible LEC with a similar promising device performance is demonstrated.
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| 29. |
- Ferry, Anders, et al.
(författare)
-
Connectivity, ionic interactions, and migration in a fast-ion-conducting polymer-in-salt electrolyte based on poly(acrylonitrile) and LiCF3SO3
- 1999
-
Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 86:4, s. 2346-2348
-
Tidskriftsartikel (refereegranskat)abstract
- The ionic conductivity of a polymeric fast-ion-conductor based on LiCF3SO3 salt and poly(acrylonitrile), [CH2CH(CN)]n), is enhanced by ∼5 orders of magnitude when the composition approaches the "polymer-in-salt" regime; i.e., when the salt content increases from N:Li=12:1 to 1.2:1 (or ∼70 wt % of salt). This is in contrast to common salt-in-polymer electrolytes where a conductivity maximum typically is encountered at intermediate compositions. We suggest that connectivity effects in a microscopically phase segregated material may influence the long-range migration of charge carriers. Conductivity data are augmented with Raman spectroscopic investigations, thus probing microscopic details regarding the state of the dissolved salt.
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| 30. |
- Ferry, Anders, et al.
(författare)
-
NMR and Raman studies of a novel fast-ion-conducting polymer-in-salt electrolyte based on LiCF3SO3 and PAN
- 2000
-
Ingår i: Electrochimica Acta. - : Elsevier. - 0013-4686 .- 1873-3859. ; 45:8-9, s. 1237-1242
-
Tidskriftsartikel (refereegranskat)abstract
- We report spectroscopic results from investigations of a novel solid polymeric fast-ion-conductor based on poly(acrylonitrile), (PAN, of repeat unit [CH2CH(CN)]n), and the salt LiCF3SO3. From NMR studies of the temperature and concentration dependencies of 7Li- and 1H-NMR linewidths, we conclude that significant ionic motion occurs at temperatures close to the glass transition temperature of these polymer-in-salt electrolytes, in accordance with a recent report on the ionic conductivity. In the dilute salt-in-polymer regime, however, ionic motion appears mainly to be confined to local salt-rich domains, as determined from the dramatic composition dependence of the ionic conductivity. FT-Raman spectroscopy is used to directly probe the local chemical anionic environment, as well as the Li+-PAN interaction. The characteristic δs(CF3) mode of the CF3SO3- anion at ∼ 750-780 cm-1 shows that the ionic substructure is highly complex. Notably, no spectroscopic evidence of free anions is found even at relatively salt-depleted compositions (e.g. N:Li ∼ 60-10:1). A strong Li+-PAN interaction is manifested as a pronounced shift of the characteristic polymer C=N stretching mode, found at ∼2244 cm-1 in pure PAN, to ∼ 2275 cm-1 for Li+-coordinated C=N moieties. Our proton-NMR data suggest that upon complexation of PAN with LiCF3SO3, the glass transition occurs at progressively lower temperatures.
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| 31. |
- Filate, Tadele Tamenu, 1994, et al.
(författare)
-
Hydrophilic Conjugated Polymers for Sustainable Fabrication of Deep-Red Light-Emitting Electrochemical Cells
- 2024
-
Ingår i: Advanced Materials Technologies. - : John Wiley & Sons. - 2365-709X. ; 9:3
-
Tidskriftsartikel (refereegranskat)abstract
- It is crucial to develop functional electronic materials that can be processed from green solvents to achieve environmentally sustainable and cost-efficient printing fabrication of organic electronic devices. Here, the design and cost-efficient synthesis of two hydrophilic and emissive conjugated polymers, TQ-OEG and TQ2F-OEG, are presented, which are rendered hydrophilic through the grafting of oligo(ethylene glycol) (OEG) solubilizing groups onto the thiophene-quinoxaline conjugated backbone and thereby can be processed from a water:ethanol solvent mixture. It is shown that the introduction of the OEG groups enables for a direct dissolution of salts by the neat polymer for the attainment of solid-state ion mobility. These properties are utilized for the design and development of light-emitting electrochemical cells (LECs), the active materials of which can be solution cast from a water:ethanol-based ink. It is specifically shown that such an LEC device, comprising an optimized blend of the TQ2F-OEG emitter and a Li salt as the active material positioned between two air-stabile electrodes, delivers deep-red emission (peak wavelength = 670 nm) with a radiance of 185 µW m−2 at a low drive voltage of 2.3 V. This study contributes relevant information as to how polymers and LEC devices can be designed and fabricated to combine functionality with sustainability.
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| 32. |
- Gerz, Isabelle, et al.
(författare)
-
Oligomer Electrolytes for Light-Emitting Electrochemical Cells : Influence of the End Groups on Ion Coordination, Ion Binding, and Turn-on Kinetics
- 2019
-
Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 11:43, s. 40372-40381
-
Tidskriftsartikel (refereegranskat)abstract
- The electrolyte is an essential constituent of the light-emitting electrochemical cell (LEC), since its operating mechanism is dependent on the redistribution of mobile ions in the active layer. Recent developments of new ion transporters have yielded high-performance devices, but knowledge about the interactions between the ionic species and the ion transporters and the influence of these interactions on the LEC performance is lacking. We therefore present a combined computational and experimental effort that demonstrates that the selection of the end group in a star-branched oligomeric ion transporter based on trimethylolpropane ethoxylate has a paramount influence on the ionic interactions in the electrolyte and thereby also on the performance of the corresponding LECs. With hydroxyl end groups, the the salt is strongly coordinated to the ion transporter, which leads to suppression of ion pairing, but the penalty is a hindered ion release and a slow turn-on for the LEC devices. With methoxy end groups, an intermediate coordination strength is seen together with the formation of contact ion pairs, but the LEC performance is very good with fast turn-on. Using a series of ion transporters with alkyl carbonate end groups, the ion transporter:cation coordination strength is lowered further, but the turn-on kinetics are slower than what is seen for devices comprising the methoxy end-capped ion transporter.
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| 33. |
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| 34. |
- Huseynova, Gunel, et al.
(författare)
-
Chemical doping to control the in-situ formed doping structure in light-emitting electrochemical cells
- 2023
-
Ingår i: Scientific Reports. - : Springer Nature. - 2045-2322. ; 13:1
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 35. |
- Jin, Xu, et al.
(författare)
-
Challenging conventional wisdom : finding high-performance electrodes for light-emitting electrochemical cells
- 2018
-
Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 10:39, s. 33380-33389
-
Tidskriftsartikel (refereegranskat)abstract
- The light-emitting electrochemical cell (LEC) exhibits capacity for efficient charge injection from two air stable electrodes into a single-layer active material, which is commonly interpreted as implying that the LEC operation is independent of the electrode selection. Here, we demonstrate that this is far from the truth and that the electrode selection instead has a strong influence on the LEC performance. We systematically investigate 13 different materials for the positive anode and negative cathode in a common LEC configuration with the conjugated polymer Super Yellow as the electroactive emitter and find that Ca, Mn, Ag, Al, Cu, indium tin oxide (ITO), and Au function as the LEC cathode, whereas ITO and Ni can operate as the LEC anode. Importantly, we demonstrate that the electrochemical stability of the electrode is paramount and that particularly electrochemical oxidation of the anode can prohibit the functional LEC operation. We finally report that it appears preferable to design the device so that the heights of the injection barriers at the two electrode/active material interfaces are balanced in order to mitigate electrode-induced quenching of the light emission. As such, this study has expanded the set of air-stable electrode materials available for functional LEC operation and also established a procedure for the evaluation and design of future efficient electrode materials.
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| 36. |
- Kirch, Anton, et al.
(författare)
-
Tuning charge-transfer states by interface electric fields
- 2024
-
Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 16:24, s. 31407-31418
-
Tidskriftsartikel (refereegranskat)abstract
- Intermolecular charge-transfer (CT) states are extended excitons with a charge separation on the nanometer scale. Through absorption and emission processes, they couple to the ground state. This property is employed both in light-emitting and light-absorbing devices. Their conception often relies on donor-acceptor (D-A) interfaces, so-called type-II heterojunctions, which usually generate significant electric fields. Several recent studies claim that these fields alter the energetic configuration of the CT states at the interface, an idea holding prospects like multicolor emission from a single emissive interface or shifting the absorption characteristics of a photodetector. Here, we test this hypothesis and contribute to the discussion by presenting a new model system. Through the fabrication of planar organic p-(i-)n junctions, we generate an ensemble of oriented CT states that allows the systematic assessment of electric field impacts. By increasing the thickness of the intrinsic layer at the D-A interface from 0 to 20 nm and by applying external voltages up to 6 V, we realize two different scenarios that controllably tune the intrinsic and extrinsic electric interface fields. By this, we obtain significant shifts of the CT-state peak emission of about 0.5 eV (170 nm from red to green color) from the same D-A material combination. This effect can be explained in a classical electrostatic picture, as the interface electric field alters the potential energy of the electric CT-state dipole. This study illustrates that CT-state energies can be tuned significantly if their electric dipoles are aligned to the interface electric field.
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| 37. |
- Kotewicz, Krzysztof, 1995, et al.
(författare)
-
Mild and Efficient Extraction of Fluorescent Chlorophyll a from Spinach Leaves for Application as the Sustainable Emitter in Light-Emitting Electrochemical Cells
- 2024
-
Ingår i: ChemElectroChem. - : Wiley-VCH Verlagsgesellschaft. - 2196-0216. ; 11:5
-
Tidskriftsartikel (refereegranskat)abstract
- Natural pigments are sustainable compounds that can be employed as emitters, sensors and sensitisers in optoelectronics. The most abundant pigment, chlorophyll, offers advantages of easily available and plentiful feedstock, biodegradability and non-toxicity. However, strenuous extraction and separation limit its application on larger scale. In this work, a practically mild and scalable extraction and separation method for rapid isolation of chlorophyll a from spinach is presented. Three different stationary phases for column chromatography were evaluated, and a new solvent system was developed for the elution of chlorophyll a on a neutral alumina chromatography column. The purified product was obtained with a yield of 0.98 mg ⋅ g−1 with respect to the dry leaves. A first light-emitting electrochemical cell (LEC) based on chlorophyll a as the emitter is reported, using the extracted chlorophyll a as the guest compound dispersed in a blend-host matrix in a concentration of 2.5 or 5 mass %. The higher-chlorophyll-concentration LEC exhibits emission solely from the chlorophyll emitter, with the main emission peak located at 675 nm. The lower-chlorophyll-concentration LEC features two distinct emission bands, one in the red region that is originating from the chlorophyll guest and one in the blue region (main peak at 430 nm) that stems from the blend host. This combined red:blue emission can be attractive for, e. g., greenhouse applications, since it matches the action spectrum of plant photosynthesis.
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| 38. |
- Larsen, Christian, et al.
(författare)
-
A tool for identifying green solvents for printed electronics
- 2021
-
Ingår i: Nature Communications. - : Nature research. - 2041-1723. ; 12
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 39. |
- Lindh, E. Mattias, 1986-, et al.
(författare)
-
Inkjet Printed Bilayer Light-Emitting Electrochemical Cells for Display and Lighting Applications
- 2014
-
Ingår i: Small. - : John Wiley & Sons. - 1613-6810 .- 1613-6829. ; 10:20, s. 4148-4153
-
Tidskriftsartikel (refereegranskat)abstract
- A new bilayer light-emitting electrochemical cell (LEC) device, which allows well-defined patterned light emission through an easily adjustable, mask-free, and additive fabrication process, is reported. The bilayer stack comprises an inkjet-printed lattice of micrometer-sized electrolyte droplets, in a filled or patterned lattice configuration. On top of this, a thin layer of light-emitting compound is deposited from solution. The light emission is demonstrated to originate from regions proximate to the interfaces between the inkjetted electrolyte, the light-emitting compound, and one electrode, where bipolar electron/hole injection and electrochemical doping are facilitated by ion motion. By employing KCF3SO3 in poly(ethylene glycol) as the electrolyte, Super Yellow as the light-emitting compound, and two air-stabile electrodes, it is possible to realize filled lattice devices that feature uniform yellow-green light emission to the naked eye, and patterned lattice devices that deliver well-defined and high-contrast static messages with a pixel density of 170 PPI.
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| 40. |
- Lindh, E. Mattias, 1986-
(författare)
-
On the operation of light-emitting electrochemical cells
- 2019
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 41. |
- Lindh, E. Mattias, 1986-, et al.
(författare)
-
Optical analysis of light-emitting electrochemical cells
- 2019
-
Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 9
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 42. |
- Lindh, E. Mattias, et al.
(författare)
-
The Weak Microcavity as an Enabler for Bright and Fault-tolerant Light-emitting Electrochemical Cells
- 2018
-
Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 8
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 43. |
- Liu, Yong-feng, et al.
(författare)
-
Carbon nanodots : a metal-free, easy-to-synthesize, and benign emitter for light-emitting electrochemical cells
- 2022
-
Ingår i: Nano Reseach. - : Springer. - 1998-0124 .- 1998-0000. ; 15:6, s. 5610-5618
-
Tidskriftsartikel (refereegranskat)abstract
- Light-emitting electrochemical cells (LECs) can be fabricated with cost-efficient printing and coating methods, but a current drawback is that the LEC emitter is commonly either a rare-metal complex or an expensive-to-synthesize conjugated polymer. Here, we address this issue through the pioneering employment of metal-free and facile-to-synthesize carbon nanodots (CNDs) as the emitter in functional LEC devices. Circular-shaped (average diameter = 4.4 nm) and hydrophilic CNDs, which exhibit narrow cyan photoluminescence (peak = 485 nm, full width at half maximum = 30 nm) with a high quantum yield of 77% in dilute ethanol solution, were synthesized with a catalyst-free, one-step solvothermal process using low-cost and benign phloroglucinol as the sole starting material. The propensity of the planar CNDs to form emission-quenching aggregates in the solid state was inhibited by the inclusion of a compatible 2,7-bis(diphenylphosphoryl)-9,9′-spirobifluorene host compound, and we demonstrate that such pristine host-guest CND-LECs turn on to a peak luminance of 118 cd·m−2 within 5 s during constant current-density driving at 77 mA·cm−2.
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| 44. |
- Liu, Yong-feng, et al.
(författare)
-
Highly Soluble CsPbBr3 Perovskite Quantum Dots for Solution-Processed Light-Emission Devices
- 2021
-
Ingår i: ACS Applied Nano Materials. - : American Chemical Society (ACS). - 2574-0970. ; , s. 1162-1174
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Tidskriftsartikel (refereegranskat)abstract
- We report on the synthesis of CsPbBr3 perovskite quantum dots (PeQDs) with a high solubility of 75 g/L in toluene and a good film-forming property, as enabled by a dense layer of didodecyldimethylammonium bromide and octanoic acid surface ligands. The crystalline and monodisperse PeQDs feature a cubic-like shape, with an edge length of 10.1 nm, and a high photoluminescence quantum yield of greater than 90% in toluene solution and 36% as a thin film. We find that the PeQDs are n-type doped following the synthesis but also that they can be p-type and additionally n-type doped by in situ electrochemistry. These combined properties render the PeQDs interesting for the emitter in solution-processed light-emitting electrochemical cells (LECs), and we report a PeQD-LEC with air-stabile electrodes that emits with a narrow emission spectrum (λpeak = 514 nm, full width at half-maximum = 24 nm) and a luminance of 250 cd/m2 at 4 V and a luminance of 1090 cd/m2 at 6.8 V. To reach this performance, it was critical to include a thin solution-processed layer comprising p-type poly(vinyl carbazole) and a tetrahexylammonium tetrafluoroborate ionic liquid between the PeQD emission layer and the anode in order to compensate for the as-synthesized n-type doping of the PeQDs.
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| 45. |
- Liu, Yong-feng, et al.
(författare)
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Hydrophilic AgInZnS quantum dots as a fluorescent turn-on probe for Cd2+ detection
- 2021
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Ingår i: Journal of Alloys and Compounds. - : Elsevier. - 0925-8388 .- 1873-4669.
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Tidskriftsartikel (refereegranskat)abstract
- Quantum dots (QDs) are intensively studied and developed for the detection of toxic heavy metal ions, notably Cd2+. However, a severe drawback is that the probing QDs themselves often are based on highly toxic elements, such as Pb or Cd. Here, we report on a one-step aqueous synthesis of more benign and hydrophilic AgInZnS QDs using 3-mercaptopropionic acid as a ligand with a high photoluminescence quantum yield of up to 41%, which were successfully employed as a fluorescent probe with a turn-on mode for detection of Cd2+ in aqueous solutions. Specifically, we determine that the effective detection range of Cd2+ in aqueous solution is 0.1–290 μM, with the lower limit of detection being 37.8 nM. We further establish that the excellent turn-on detection of Cd2+ is due to that surface defects on the AgInZnS QDs are effectively passivated by the Cd2+, as verified by a prolonged fluorescent lifetime and an increased photoluminescence quantum yield. We finally demonstrate that the AgInZnS QD probe is capable of detecting Cd2+ in lake water samples, and that it meets the WHO standard.
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| 46. |
- Liu, Yong-feng, et al.
(författare)
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The influence of the capping ligands on the optoelectronic performance, morphology, and ion liberation of CsPbBr3 perovskite quantum dots
- 2023
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Ingår i: Nano Reseach. - : Springer Nature. - 1998-0124 .- 1998-0000. ; 16:7, s. 10626-10633
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 47. |
- Lundberg, Petter, 1988-
(författare)
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Light for a brighter morrow : paving the way for sustainable light-emitting devices
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 48. |
- Lundberg, Petter, et al.
(författare)
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Polymer Featuring Thermally Activated Delayed Fluorescence as Emitter in Light-Emitting Electrochemical Cells
- 2020
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Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 11:15, s. 6227-6234
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Tidskriftsartikel (refereegranskat)abstract
- Semiconducting polymers that feature thermally activated delayed fluorescence (TADF) can deliver a much desired combination of high-efficiency and metal-free electroluminescence and cost-efficient solution-based fabrication. A TADF polymer is thus a very good fit for the emitting compound in light-emitting electrochemical cells (LECs) because the commonly employed air-stabile and few-layer LEC architecture is well suited for such solution-based fabrication. Herein we report on the first LEC device based on a TADF polymer as the emitting species, which delivers a luminance of 96 cd m–2 at 4 V and a current efficacy of 1.4 cd A–1 and >600 cd m–2 at 6 V, which is competitive with the performance of multilayer organic light-emitting diodes based on the same TADF polymer. We further utilize the established sensitivity of the emission of the TADF polymer to its environment to draw conclusions on the exciton populations in host-guest and host-free TADF LEC devices.
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| 49. |
- Lundberg, Petter, et al.
(författare)
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Thermally activated delayed fluorescence with 7% external quantum efficiency from a light-emitting electrochemical cell
- 2019
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Ingår i: Nature Communications. - : Nature Publishing Group. - 2041-1723. ; 10
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 50. |
- Matyba, Piotr, 1982-, et al.
(författare)
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Graphene and Mobile Ions: The Key to All-Plastic, Solution-Processed Light-Emitting Devices
- 2010
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Ingår i: ACS NANO. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 4:2, s. 637-642
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Tidskriftsartikel (refereegranskat)abstract
- The emerging field of "organic" or "plastic" electronics has brought low-voltage, ultrathin, and energy-efficient lighting and displays to market as organic light-emitting diode (OLED) televisions and displays in cameras and mobile phones. Despite using carbon-based materials as the light-emitting layer, previous efficient organic electronic light-emitting devices have required at least one metal electrode. Here, we utilize chemically derived graphene for the transparent cathode in an all-plastic sandwich-structure device, similar to an OLED, called a light-emitting electrochemical cell (LEC). Using a screen-printable conducting polymer as a partially transparent anode and a micro meter-thick active layer solution-deposited from a blend of a light-emitting polymer and a polymer electrolyte, we demonstrate a light-emitting device based solely on solution-processable carbon-based materials. Our results demonstrate that low-voltage, inexpensive, and efficient light-emitting devices can be made without using metals. In other words, electronics can truly be "organic".
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