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Probing ion movement in conjugated polymers
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
2019 (English)Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

Electronic conduction in conjugated polymers can be increased through electrochemical doping. This is utilised in light-emitting electrochemical cells and allows for a less demanding manufacturing process compared to the related organic light-emitting diode. The doping process requires ion transport into the conjugated polymer and has yet to be quantified for an electrolyte-free conjugated polymer.

In this project the ion movement of lithium trifluoromethanesulfonate in poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) has been studied with several electrochemical techniques: cyclic voltammetry, galvanostatic cycling, staircase potentiostatic electrochemical impedance spectroscopy and staircase potentiostatic chronoamperometry. The measurements have been performed on a dry system of spin-coated MEH-PPV films with lithium trifluoromethanesulfonate dissolved in a copolymer of poly(epsilon-caprolactone) and poly(trimethylene carbonate), PCL–PTMC, as a solid electrolyte.

Infrared spectroscopy (FTIR) showed evidence of ion association of lithium trifluoromethanesulfonate dissolved in MEH-PPV. The electrochemical analyses confirmed the possibility to insert trifluoromethanesulfonate anions into electrolyte-free MEH-PPV; extraction of the ions was also possible, albeit with limited reversibility. Insertion of lithium ions was not observed. Adding the ion transporter trimethylolpropane ethoxylate (TMPE-OH) was seen to increase the reversibility of the process. The results also indicated different ion mobilities in doped and undoped MEH-PPV. Doping of an MEH-PPV film was shown to change the behaviour of the film from capacitive to faradaic behaviour. MEH-PPV did also show indications of two different levels of p-doping, one above 3.3 V vs. Li+/Li and the other above 3.7 V, with over-oxidation occurring at potentials over 4.1 V.

Place, publisher, year, edition, pages
2019. , p. 26
Series
UPTEC K, ISSN 1650-8297 ; 18036
Keywords [en]
Light-emitting electrochemical cell, conjugated polymer, electrochemical doping, MEH-PPV, lithium, trifluoromethanesulfonate, trimethylolpropane ethoxylate
National Category
Materials Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-375743OAI: oai:DiVA.org:uu-375743DiVA, id: diva2:1284544
Educational program
Master Programme in Chemical Engineering
Supervisors
Examiners
Available from: 2019-02-01 Created: 2019-01-31 Last updated: 2019-02-01Bibliographically approved

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The full text will be freely available from 2021-01-31 23:59
Available from 2021-01-31 23:59

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