Department of Physics Umeå University
Umeå 2015
Functional and Flexible
Light-Emitting
Electrochemical Cells
Amir Asadpoordarvish
Akademisk avhandling
som med vederbörligt tillstånd av Rektor vid Umeå universitet för
avläggande av filosofie doktorsexamen framläggs till offentligt försvar i
N300, Naturvetarhuset,
Fredagen den 22 maj, kl. 10:00.
Avhandlingen kommer att försvaras på engelska.
Fakultetsopponent: Prof. Jun Gao,
Department of Physics, Engineering Physics and Astronomy, Queen’s
University, Ontario, Canada.
Organization Document type Date of publication
Umeå University Doctoral thesis 30 April 2015
Department of Physics
Author
Amir Asadpoordarvish
Title
Functional and Flexible Light-Emitting Electrochemical Cells.
Abstract
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 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.
Keywords
Ag nanowires, all-ambient fabrication, ambient-air lifetime, encapsulation, flexible, light-emitting electrochemical cells, organic light-emitting device, light-emitting paper, spray coating.
Language ISBN Number of pages English 978-91-7601-257-4 57 + 5 papers
