| 1. |
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| 2. |
- 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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| 3. |
- Fang, Junfeng, et al.
(författare)
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Identifying and Alleviating Electrochemical Side-Reactions in Light-Emitting Electrochemical Cells
- 2008
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Ingår i: Journal of the American Chemical Society.. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 130:13, s. 4562-4568
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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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| 4. |
- Fang, Junfeng, et al.
(författare)
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The design and realization of flexible light-emitting electrochemical cells with record-long lifetime
- 2009
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Ingår i: Advanced Functional Materials. - : Wiley. - 1616-301X .- 1616-3028. ; 19:16, s. 2671-2676
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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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| 5. |
- Kulshreshtha, Chandramouli, et al.
(författare)
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Investigating ultrafast carrier dynamics in perovskite solar cells with an extended π-conjugated polymeric diketopyrrolopyrrole layer for hole transportation
- 2020
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Ingår i: RSC Advances. - : Royal Society of Chemistry. - 2046-2069. ; 10:11, s. 6618-6624
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Tidskriftsartikel (refereegranskat)abstract
- Here, we show a new diketopyrrole based polymeric hole-transport material (PBDTP-DTDPP, (poly[[2,5-bis(2-hexyldecyl)-2,3,5,6-tetrahydro-3,6-dioxopyrrolo[3,4-c]pyrrole-1,4-diyl]-alt-[[2,2′-(4,8-bis(4-ethylhexyl-1-phenyl)-benzo[1,2-b:4,5-b′]dithiophene)bis-thieno[3,2-b]thiophen]-5,5′-diyl]])) for application in perovskite solar cells. The material performance was tested in a solar cell with an optimized configuration, FTO/SnO2/perovskite/PBDTP-DTDPP/Au, and the device showed a power conversion efficiency of 14.78%. The device charge carrier dynamics were investigated using transient absorption spectroscopy. The charge separation and recombination kinetics were determined in a device with PBDTP-DTDPP and the obtained results were compared to a reference device. We find that PBDTP-DTDPP enables similar charge separation time (<∼4.8 ps) to the spiro-OMeTAD but the amount of nongeminate recombination is different. Specifically, we find that the polymeric PBDTP-DTDPP hole-transport layer (HTL) slows-down the second-order recombination much less than spiro-OMeTAD. This effect is of particular importance in studying the charge transportation in optimized solar cell devices with diketopyrrole based HTL materials.
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| 6. |
- 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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| 7. |
- Matyba, Piotr, 1982-, et al.
(författare)
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On the desired properties of a conjugated polymer-electrolyte blend in a light-emitting electrochemical cell
- 2008
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Ingår i: Organic Electronics: physics, materials, applications. - : Elsevier BV. - 1566-1199 .- 1878-5530. ; 9:5, s. 699-710
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Tidskriftsartikel (refereegranskat)abstract
- We present results from a systematic study on the influence of the conjugated polymer (CP) on the performance of planar light-emitting electrochemical cells (LECs) with a device structure of Au/{CP + poly(ethylene oxide) (PEO) + KCF 3 SO 3 }/Au. We have employed six different CPs, and we demonstrate that in order to attain a fast turn-on time and a strong light emission intensity, it is critical that the p-type doping (oxidation) potential of the CP is situated within the electrochemical stability window of the {PEO + KCF 3 SO 3 } electrolyte. We also find that a high ionic conductivity of the active material correlates with a small phase separation between the CP and the {PEO + KCF 3 SO 3 } electrolyte, and that a doping concentration of ∼0.1 dopants/CP repeat unit is a generic feature of the progressing doping fronts in all investigated devices. Finally we report the first observation of a light emission zone positioned in close proximity to the positive anode in a CP-based LEC. © 2008 Elsevier B.V. All rights reserved.
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| 8. |
- Matyba, Piotr, 1982-
(författare)
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Polymer light-emitting electrochemical cells : Utilizing doping for generation of light
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The current implementation of conjugated polymers (“conducting plastics”) in a wide range of devices promises to bring the vision of a new generation of flexible, efficient and low-cost applications to reality. Plastic lightemitting devices in the form of polymer light-emitting diodes (PLEDs) are projected to be particularly close to the market in applications such as large area and conformable illumination panels and high-performance thin displays. However, two notable drawbacks of PLEDs are that they depend on vacuum deposition of a reactive metal for the negative electrode and that the active material must be extremely thin and uniform in thickness. As a consequence, PLEDs cannot be expected to allow for a low-cost continuous production using a roll-to-roll coating and/or printing process. This thesis focuses on an alternative to the PLED: A light-emitting electrochemical cell (LEC). LECs comprise a mixture of a conjugated polymer and a solid-state electrolyte as the active material positioned between two electrodes. The existence of mobile ions in the active material allows for a number of interesting attributes, both from a fundamental science and an application perspective. Importantly, the ions and the related unique operation of LECs make these devices apt for the utilization of low-cost roll-to-roll fabrication of the entire device as the electrode materials can be air stable and solution-processible and the requirement on the thickness of the active material is much less stringent than in PLEDs. The herein presented “basic science” studies primarily focus on the operation of LECs. It is for instance firmly established that a light-emitting p-n junction can form in-situ in a LEC device during the application of a voltage. This dynamic p-n junction exhibits some similarities, but also distinct differences, in comparison to the static p-n junctions that are exploited in crystalline inorganic semiconductor devices. We have also systematically explored the role that the constituent materials (ions, conjugated polymer, ionic solvent, and electrode material) can have on the performance of LECs, and two of the more important findings are that the concentration of ions can influence the doping structure in a motivated fashion and that it is critically important to consider the electrochemical stability window of the constituent materials in order to attain stable device operation. With this knowledge at hand, we have executed a number of more “applied science” studies, where we have used the acquired information from the basic-science studies for the rational design of improved devices. We have demonstrated LEC devices with significantly improved device performance, as exemplified by an orange-red device that emitted significant light (> 100 cd/m2) for more than one month of uninterrupted operation, and a yellow-green device that emitted significant light for 25 days at a low voltage of 4 V and at relatively high efficiency (6 lm/W). Finally, we have conceptualized and realized a solely solution-processed and metal-free LEC comprising graphene as the negative electrode and the conducting polymer PEDOT-PSS as the positive electrode. This type of devices represents a paradigm shift in the field of solid-state lighting as they demonstrate that it is possible to fabricate an entire light-emitting device from solution-processible and “green” carbon-based materials in a process that is akin to printing.
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| 9. |
- Matyba, Piotr, 1982-, et al.
(författare)
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The dynamic organic p-n junction
- 2009
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Ingår i: Nature Materials. - London, UK : Nature Publishing Group. - 1476-1122 .- 1476-4660. ; 8:8, s. 672-676
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Tidskriftsartikel (refereegranskat)abstract
- Static p-n junctions in inorganic semiconductors are exploited in a wide range of todays electronic appliances. Here, we demonstrate the in situ formation of a dynamic p-n junction structure within an organic semiconductor through electrochemistry. Specifically, we use scanning kelvin probe microscopy and optical probing on planar light-emitting electrochemical cells (LECs) with a mixture of a conjugated polymer and an electrolyte connecting two electrodes separated by 120 mu m. We find that a significant portion of the potential drop between the electrodes coincides with the location of a thin and distinct light-emission zone positioned andgt;30 mu m away from the negative electrode. These results are relevant in the context of a long-standing scientific debate, as they prove that electrochemical doping can take place in LECs. Moreover, a study on the doping formation and dissipation kinetics provides interesting detail regarding the electronic structure and stability of the dynamic organic p-n junction, which may be useful in future dynamic p-n junction-based devices.
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| 10. |
- Modestov, Mikhail, et al.
(författare)
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Model of the electrochemical conversion of an undoped organic semiconductor film to a doped conductor film.
- 2010
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 81:8, s. 081203(R)-
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Tidskriftsartikel (refereegranskat)abstract
- We develop a model describing the electrochemical conversion of an organic semiconductor (specifically, the active material in a light-emitting electrochemical cell) from the undoped nonconducting state to the doped conducting state. The model, an extended Nernst-Planck-Poisson model, takes into account both strongly concentration-dependent mobility and diffusion for the electronic charge carriers and the Nernst equation in the doped conducting regions. The standard Nernst-Planck-Poisson model is shown to fail in its description of the properties of the doping front. Solving our extended model numerically, we demonstrate that doping front progression in light-emitting electrochemical cells can be accurately described.
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| 11. |
- Muschet, Alexander, 1990-
(författare)
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Non-linear attosecond physics at 100 eV
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Non-linear interactions between light and matter have nowadays a broad range of applications. They are used for frequency doubling in simple laser pointers as well as for a variety of purposes in complex laser systems like the one presented in this thesis. For the study of ultrafast phenomena, those non-linear interactions are crucial to trigger and observe events at the fastest timescale, which is currently the attosecond regime (10-15 – 10-18 s). As the duration of a single optical cycle of a visible light wave is longer than this timescale, these investigations necessitate the application of XUV and X-ray pulses. However, the generation of isolated attosecond light pulses sufficiently intense to initiate non-linear interactions with matter is restricted to photon energies below 50 eV. The aim of this thesis is to establish a new light source, which pushes this boundary further and thereby enables the observation of up to now unrevealed electron dynamics.The presented new light source provides attosecond pulses with approximately hundred times more pulse energy than typical systems (up to 55 nJ in the spectral range from approximately 65 eV to 140 eV). This facilitates non-linear measurements at these photon energies. The achieved high energy stability (5 %) of this light source allows precise and time efficient measurements. These parameters are obtained via energy-upscaling of high-harmonic generation in gas medium. For the generation of well isolated attosecond pulses a unique laser, like the Light Wave Synthesizer 20, is necessary. This laser uses optical parametric synthesis to produce the most intense sub-5 fs, sub two-cycle laser pulses in the world (80 mJ, 4.5 fs).Furthermore, an optimal focus of the XUV pulses is crucial to provide the necessary intensity for non-linear interactions. Therefore, different methods for focusing the XUV pulses are investigated. Moreover, the construction and characterization of a robust split and delay stage is presented, which is essential for time resolved measurements.The detection of the non-linear interaction is realized via a spatially resolved ion time-of-flight detector, the ion microscope. This allows for a quantitative measurement of different ionization states. With the combination of this detector and the new light source the non-linear generation of Xe4+ and Xe5+ at photon energies around 100 eV is demonstrated. This enables the determination of the two-photon ionization cross-sections, which could up to now only be measured with much longer pulses at large scientific infrastructures. This paves the way towards time-resolved XUV pump – XUV probe measurements at 100 eV.
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| 12. |
- Sandström, Andreas, et al.
(författare)
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Separating Ion and Electron Transport: The Bilayer Light-Emitting Electrochemical Cell
- 2010
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Ingår i: JOURNAL OF THE AMERICAN CHEMICAL SOCIETY. - : ACS American Chemical Society. - 0002-7863 .- 1520-5126. ; 132:19, s. 6646-
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Tidskriftsartikel (refereegranskat)abstract
- The current generation of polymer light-emitting electrochemical cells (LECs) suffers from insufficient stability during operation. One identified culprit is the active material, which comprises an intimate blend between an ion-conducting electrolyte and an electron-transporting conjugated polymer, as it tends to undergo phase separation during long-term operation and the intimate contact between the ion- and electron-transporting components provokes side reactions. To address these stability issues, we present here a bilayer LEC structure in which the electrolyte is spatially separated from the conjugated polymer. We demonstrate that employing this novel device structure, with its clearly separated ion- and electron-transport paths, leads to distinctly improved LEC performance in the form of decreased turn-on time and improved light emission. We also point out that it will allow for the utilization of combinations of active materials having mutually incompatible solubilities.
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| 13. |
- Sandström, Andreas, et al.
(författare)
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Yellow-green light-emitting electrochemical cells with long lifetime and high efficiency
- 2010
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 96:5, s. 053303-
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Tidskriftsartikel (refereegranskat)abstract
- We show that the electrochemical stability window of the constituent components in light-emitting electrochemical cells (LECs), e.g., the electrolyte, should be considered in order to minimize undesired side reactions. By designing and operating LECs in accordance with straightforward principles, we demonstrate sandwich cells that turn on fast at room temperature (<2 s), and which emit significant yellow-green light (>100 cd/m2) during 25 days of uninterrupted operation at low voltage (<4 V) and high power conversion efficacy ~6 lm/W. We further demonstrate that it is possible to attain balanced p- and n-type doping and a centered p-n junction in such planar LECs based on the conjugated polymer “superyellow.”
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| 14. |
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| 15. |
- van Reenen, Stephan, et al.
(författare)
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A Unifying Model for the Operation of Light-Emitting Electrochemical Cells
- 2010
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society. - 0002-7863 .- 1520-5126. ; 132:39, s. 13776-13781
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Tidskriftsartikel (refereegranskat)abstract
- The application of doping in semiconductors plays a major role in the high performances achieved to date in inorganic devices. In contrast, doping has yet to make such an impact in organic electronics. One organic device that does make extensive use of doping is the light-emitting electrochemical cell (LEC), where the presence of mobile ions enables dynamic doping, which enhances carrier injection and facilitates relatively large current densities. The mechanism and effects of doping in LECs are, however, still far from being fully understood, as evidenced by the existence of two competing models that seem physically distinct: the electrochemical doping model and the electrodynamic model. Both models are supported by experimental data and numerical modeling. Here, we show that these models are essentially limits of one master model, separated by different rates of carrier injection. For ohmic nonlimited injection, a dynamic p-n junction is formed, which is absent in injection-limited devices. This unification is demonstrated by both numerical calculations and measured surface potentials as well as light emission and doping profiles in operational devices. An analytical analysis yields an upper limit for the ratio of drift and diffusion currents, having major consequences on the maximum current density through this type of device.
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| 16. |
- van Reenen, Stephan, et al.
(författare)
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Salt concentration effects in planar light-emitting electrochemical cells
- 2011
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Ingår i: Advanced Functional Materials. - : Wiley-VCH Verlagsgesellschaft. - 1616-301X .- 1616-3028. ; 21:10, s. 1795-1802
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Tidskriftsartikel (refereegranskat)abstract
- Incorporation of ions in the active layer of organic semiconductor devices may lead to attractive device properties like enhanced injection and improved carrier transport. In this paper, we investigate the effect of the salt concentration on the operation of light-emitting electrochemical cells, using experiments and numerical calculations. The current density and light emission are shown to increase linearly with increasing ion concentration over a wide range of concentrations. The increasing current is accompanied by an ion redistribution, leading to a narrowing of the recombination zone. Hence, in absence of detrimental side reactions and doping-related luminescence quenching, the ion concentration should be as high as possible.
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