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Doping-Induced Self-Absorption in Light-Emitting Electrochemical Cells
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
2014 (Engelska)Ingår i: ACS Photonics, E-ISSN 2330-4022, Vol. 1, nr 3, s. 182-189Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

We report on the quantitative effects of doping-induced self-absorption in light-emitting electrochemical cells (LECs) as a function of active material (AM) thickness and doping concentration. For state-of-the-art polymer LECs with optimized doping concentration and comprising Super Yellow as the electroluminescent (EL) polymer and poly(ethylene oxide)-KCF3SO3 as the electrolyte, we find that the self-absorption loss at the EL peak wavelength is similar to 10% for a 100 nm thin AM and >70% for a 1 mu m thick AM. This implies that the utilization of micrometer-thick AMs fit for fault-tolerant large-scale fabrication can be concomitant with a notable penalty in device performance, and that spatial variations in AM thickness will be manifested in a corresponding spatial light-intensity variation. Moreover, we find that inclusion of a poly(ethylene oxide)-KCF3SO3 electrolyte can inhibit the out-coupling of light and suggest that the culprit is light scattering from dispersed crystalline-electrolyte domains. Finally, we demonstrate evidence for that the selected initial salt concentration in an LEC device dictates the maximum doping concentration that can be attained at steady-state operation.

Ort, förlag, år, upplaga, sidor
2014. Vol. 1, nr 3, s. 182-189
Nyckelord [en]
light-emitting device, organic electronics, electroluminescence, electrochemical doping, cyclic voltammetry, conjugated polymer
Nationell ämneskategori
Fysik
Identifikatorer
URN: urn:nbn:se:umu:diva-90793DOI: 10.1021/ph400050tISI: 000335802900006OAI: oai:DiVA.org:umu-90793DiVA, id: diva2:753947
Tillgänglig från: 2014-10-09 Skapad: 2014-07-01 Senast uppdaterad: 2018-06-14Bibliografiskt granskad
Ingår i avhandling
1. Functional and Flexible Light-Emitting Electrochemical Cells
Öppna denna publikation i ny flik eller fönster >>Functional and Flexible Light-Emitting Electrochemical Cells
2015 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

The introduction of artificial illumination has brought extensive benefits to mankind, and during the last years we have seen a tremendous progress in this field with the introduction of the energy-efficient light-emitting diode (LED) and the high-contrast organic LED display. These high-end technologies are, however, produced using costly and complex processes, and it is anticipated that the next big thing in the field will be the advent of a low-cost and “green” illumination technology, which can be fabricated in a cost- and material-efficient manner using non-toxic and abundant raw materials, and which features attractive form factors such as flexibility, robustness and light-weight. The light-emitting electrochemical cell (LEC) is a newly invented illumination technology, and in this thesis we present results that imply that it can turn the above vision into reality.

The thin-film LEC comprises an active material sandwiched between a cathode and an anode as its key constituent parts. With the aid of a handheld air-brush, we show that functional large-area LECs can be fabricated by simply spraying three layers of solution -- forming the anode, active material, and cathode -- on top of a substrate. We also demonstrate that such “spray-sintered” LECs can feature multicolored emission patterns, and be fabricated directly on complex-shaped surfaces, with one notable example being the realization of a light-emission fork!

Almost all LECs up-to-date have been fabricated on glass substrates, but for a flexible and light-weight emissive device, it is obviously relevant to identify more appropriate substrate materials. For this end, we show that it is possible to spray-coat the entire LEC directly on conventional copy paper, and that such paper-LECs feature uniform light-emission even under heavy bending and flexing.

We have further looked into the fundamental aspects of the LEC operation and demonstrated that the in-situ doping formation, which is a characteristic and heralded feature of LECs, can bring problems in the form of doping-induced self-absorption. By quantitatively analyzing this phenomenon, we provided straightforward guidelines on how future efficiency-optimized LEC devices should be designed.

The in-situ doping formation process brings the important advantage that LECs can be fabricated from solely air-stabile materials, but during light emission the device needs to be protected from the ambient air. We have therefore developed a functional glass/epoxy encapsulation procedure for the attainment of LEC devices that feature a record-long ambient-air operational lifetime of 5600 h. For the light-emission device of the future, it is however critical that the encapsulation is flexible, and in our last study, we show that the use of multi-layer barrier can result in high-performance flexible LECs.

Ort, förlag, år, upplaga, sidor
Umeå: Umeå University, 2015. s. 57
Nyckelord
all-ambient fabrication, ambient-air lifetime, encapsulation, flexible, light-emitting electrochemical cells, light-emitting paper
Nationell ämneskategori
Nanoteknik Annan fysik
Forskningsämne
fysik
Identifikatorer
urn:nbn:se:umu:diva-102400 (URN)978-91-7601-257-4 (ISBN)
Disputation
2015-05-22, N300, Naturvetarhuset, Umeå University, Umeå, 10:00 (Engelska)
Opponent
Handledare
Tillgänglig från: 2015-04-30 Skapad: 2015-04-23 Senast uppdaterad: 2018-06-07Bibliografiskt granskad

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Kaihovirta, NikolaiAsadpoordarvish, AmirEdman, Ludvig

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