| 1. |
- 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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| 2. |
- 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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| 3. |
- 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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| 4. |
- Matyba, Piotr, 1982-, et al.
(författare)
-
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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| 5. |
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