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Flexible and Metal-Free Light-Emitting Electrochemical Cells Based on Graphene and PEDOT-PSS as the Electrode Materials
Umeå University, Faculty of Science and Technology, Department of Physics. (The Organic Photonics and Electronics Group)
Rutgers University.
Rutgers University.
Linköpings universitet.
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2011 (English)In: ACS Nano, ISSN 1936-0851, Vol. 5, no 1, 574-580 p.Article in journal (Refereed) Published
Abstract [en]

We report flexible and metal-free light-emitting electrochemical cells (LECs) using exclusively solution-processed organic materials and illustrate interesting design opportunities offered by such conformable devices with transparent electrodes. Flexible LEC devices based on chemically derived graphene (CDG) as the cathode and poly(3,4-ethylenedioxythiophene) mixed with poly(styrenesulfonate) as the anode exhibit a low turn-on voltage for yellow light emission (V = 2.8 V) and a good efficiency 2.4 (4.0) cd/A at a brightness of 100 (50) cd/m2. We also find that CDG is electrochemically inert over a wide potential range (+1.2 to −2.8 V vsferrocene/ferrocenium) and exploit this property to demonstrate planar LEC devices with CDG as both the anode and the cathode.

Place, publisher, year, edition, pages
Washington D.C.: American Chemical Society , 2011. Vol. 5, no 1, 574-580 p.
Keyword [en]
light-emitting electrochemical cell, metal-free, flexible, solution processing, graphene, superyellow, PEDOT-PSS, doping, p−n junction
National Category
Condensed Matter Physics
URN: urn:nbn:se:umu:diva-48543DOI: 10.1021/nn102704hOAI: diva2:450796
Available from: 2011-10-21 Created: 2011-10-21 Last updated: 2012-06-29Bibliographically approved
In thesis
1. Polymer light-emitting electrochemical cells: Utilizing doping for generation of light
Open this publication in new window or tab >>Polymer light-emitting electrochemical cells: Utilizing doping for generation of light
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

    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.

Place, publisher, year, edition, pages
Umeå: Department of Physics, Umeå University, 2011. 67 p.
urn:nbn:se:umu:diva-38953 (URN)978-91-7459-124-8 (ISBN)
Public defence
2011-02-04, Mit-huset, MA 121, Umeå universitet, Umeå, 09:00 (English)
Available from: 2011-01-13 Created: 2011-01-11 Last updated: 2012-06-29Bibliographically approved

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