Preparation and stability of poly(3,4-ethylenedioxythiophene) thin films for transparent electrode applications

Date

2018-07-05

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Abstract

Juhtivad polümeerid on sellised orgaanilised polümeerid, mis juhivad elektrit. See põnev materjalide klass on juba 20. sajandi lõpust pälvinud teadusmaailma suurt tähelepanu, sest võib osutuda kasulikuks paljudes erinevates rakendustes, alates sensoritest ja lõpetades päikesepatareidega. Näiteks on paljudes seadmetes vaja kasutada läbipaistvaid elektroode, mille materjaliks on tänapäeval harilikult indiumtinaoksiidi (ITO) kiled. Aga ITO kiled on kallid ja nendele oleks hea odavam asendus leida. Just siin võib juhtiv polümeer kasuks tulla. Erinevalt ITOst on juhtivad polümeerid ka hea painduvusega, mis võimaldaks valmistada painduvaid elektroonikaseadmeid. Polü(3,4-etüleendioksütiofeen) (PEDOT) on üks juhtiv polümeer, mis võiks läbipaistvaks elektroodimaterjaliks sobida. PEDOT on üsna kõrge juhtivuse, hea läbipaistvuse ning juhtivate omaduste küllaltki suure stabiilsusega. Paraku ei ole ükski neist omadustest siiski veel päris ideaalne, mistõttu tuleb otsida lahendusi nende omaduste parandamiseks. Antud doktoritöös uuriti kahte erinevat PEDOTi õhukeste kilede valmistamise meetodit. Ühe meetodi puhul pärineb polümeeri moodustav monomeer gaasifaasist ja teisel juhul lahusest. Määrati, millistes etappides kile kasv toimub ja kuidas saada paremate omadustega kilet. Uuriti ka PEDOTi kilede vananemist ja nende juhtivuse vastupidavust erinevates keskkondades. Selgus, et uuritud PEDOTi kiled ei juhi elektrit nii hästi kui ITO ja nende juhtivus ei ole ka nii stabiilne. Ent avastati siiski üks rakendus, milles PEDOT on ITOst parem. Triboelektriline nanogeneraator on energiatootmisseade, mis suudab toota elektrit ka väikeste igapäevaelu liikumiste mehaanilisest energiast, mis muidu raisku läheb. PEDOTi kile kasutamine sellise seadme elektroodimaterjalina võimaldab kolm korda suuremat võimsustihedust kui ITO ja PEDOTi kile on selleks ka piisavalt stabiilne.
Conductive polymers are organic polymers, which conduct electricity. This fascinating class of materials has gained a lot of scientific attention starting already from the end of the 20th century, because it may become useful in numerous applications, from sensors to solar panels. For example, transparent electrodes consisting of indium tin oxide (ITO) films are used in a large number of devices. But ITO films are expensive and a cheaper solution would be greatly appreciated. For this purpose, a conductive polymer may be a better solution. Conductive polymers are also flexible while ITO is brittle, enabling preparation of flexible electronic devices. Poly(3,4-ethylenedioxythiphene) (PEDOT) is a conductive polymer, which could be used as a transparent electrode material. PEDOT has a relatively high conductivity, good transparency and quite stable conductive properties. However, none of these properties is perfect at the current level of development. Therefore, it is still necessary to find ways for improving these properties. Two different preparation methods for PEDOT thin films were studied in this thesis. For one method the source of polymerizing monomer is a gas phase, for another method a solution. During this work the stages of film growth were investigated and better film formation conditions were determined. Aging of PEDOT and stability of conductance were investigated in different conditions. It was found out that investigated PEDOT films are not so highly conductive and stable conductors as ITO. However, in one application PEDOT was better than ITO. A triboelectric nanogenerator is a device, which could produce electricity from the mechanical energy of small movements, which would be otherwise wasted. As an electrode material for this device, PEDOT film enables to have three times higher power densities than ITO film and it is sufficiently stable.

Description

Väitekirja elektrooniline versioon ei sisalda publikatsioone

Keywords

polymerization, polymer films, surface chemistry

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