Nanostructured thermoelectric materials for transparent and flexible applications

Tomi Koskinen

Nanostructured thermoelectric materials for transparent and flexible applications

Julkaisun otsikon käännös: Nanorakenteiset lämpösähköiset materiaalit läpinäkyviin ja taipuisiin sovelluksiin

Tomi Koskinen

Tutkimustuotos: Doctoral Thesis › Collection of Articles

Abstrakti

Energian kulutuksen arvioidaan kasvavan lähivuosikymmeninä jopa 50%, mikä rasittaa energiantuotantoketjua ja asettaa vaatimuksia käyttämämme teknologian energiatehokkuudelle. Valtaosa kulutetusta primäärienergiasta menetetään hukkalämpönä, jota esiintyy kaikkialla hankalasti hyödynnettävässä muodossa. Samaan aikaan sähköisten laitteiden määrä niin arkikäytössä kuin teollisuudessakin kasvaa nopeasti. Lämpösähköiset materiaalit mahdollistavat lämmön muuntamisen sähköksi, mutta heikko teho-kustannussuhde hidastaa niiden yleistymistä. Materiaalien sähköisten- ja lämpöominaisuuksien muokkaaminen nanorakenteistamalla kuitenkin mahdollistaa näiden materiaalien suorituskyvyn kasvattamisen. Nanorakenteistamalla on mahdollista parantaa myös materiaalien muita ominaisuuksia, kuten läpinäkyvyyttä tai taipuisuutta. Tällaisilla funktionaalisilla ominaisuuksilla varustettujen lämpösähköisten materiaalien saatavuus voi edistää lämpösähköisten laitteiden yleistymistä uusien käyttökohteiden ja sovellusten kautta. Tämä väitöskirja esittelee tapoja toteutta nanorakenteistamista hyödyntäviä lämpösähköisiä materiaaleja sekä näihin materiaaleihin pohjautuvia laitteita. Väitöskirjassa tutkitaan ensin lämpöominaisuuksia kuori-vaippa GaAs-AlAs -nanolankahiloissa, joka on tärkeä materiaali etenkin optoelektroniikan sovelluksissa. Transientilla lämpöreflektanssimittauksella havaitaan epitaksiaalisen AlAs-vaipan paksuuden vaikuttavan heterorakenteen lämpöominaisuuksiin.Seuraavaksi tutkitaan läpinäkyvän lämpösähköisen materiaalin, ZnO:n, ominaisuuksia atomikerroskasvatetuista (ALD) kalvoista. Zirkonin kasvattamisen ZnO-kerrosten väliin havaitaan parantavan lämpösähköisiä ominaisuuksia huoneenlämmössä 2% nimellisellä zirkonkonsentraatiolla. Kun nanohuokoista ruohonkaltaista alumiinioksidia (GLA) käytetään Al-seostetun ZnO:n (AZO) kasvatusalustana, havaitaan kasvanut varauksenkuljettajatiheys ja tästä seuraava parannus sekä sähkönjohtavuudessa että tehokertoimessa. Lisäksi GLA:n päälle kasvatetun AZO:n läpinäkyvyyden havaitaan parantuvan GLA:lta osittain periytyvän heijastamattomuuden ansiosta. Lopuksi nanorakenteisia materiaaleja käytetään kahden erityyppisen taipuisan lämpösähköisen laitteen toteutuksessa. Ensin esitellään suoraan taipuisalle muoville kasvatettuihin InAs-nanolankaverkkoihin pohjautuva lämpösähköinen generaattori, minkä jälkeen esitellään ruiskupinnoitettua grafeenikalvoa hyödyntävä passiivinen lämpötilajakauma-anturi. Työn tulokset esittävät tapoja toteuttaa funktionaalisiin sovelluksiin sopivia lämpösähköisiä materiaaleja. Esitellyt lähestymistavat mahdollistavat skaalautuvaa ja kustannustehokasta materiaalien valmistusta, viitoittaen siten tietä kohti funktionaalisten lämpösähköisten laitteiden hyödyntämistä käytännön sovelluksissa.

Julkaisun otsikon käännös	Nanorakenteiset lämpösähköiset materiaalit läpinäkyviin ja taipuisiin sovelluksiin
Alkuperäiskieli	Englanti
Pätevyys	Tohtorintutkinto
Myöntävä instituutio	Aalto-yliopisto
Valvoja/neuvonantaja	Tittonen, Ilkka, Vastuuprofessori
Kustantaja	Aalto University
Painoksen ISBN	978-952-64-1374-7
Sähköinen ISBN	978-952-64-1375-4
Tila	Julkaistu - 2023
OKM-julkaisutyyppi	G5 Artikkeliväitöskirja

Tutkimusalat

lämpösähköinen ilmiö
nanorakenteet
ohutkalvot

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http://urn.fi/URN:ISBN:978-952-64-1375-4

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Repo, P. (Manager) & Rissanen, A. (Other)
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@phdthesis{5b1a75505f7f4e0883b698b10971ca5a,

title = "Nanostructured thermoelectric materials for transparent and flexible applications",

abstract = "The global energy use is predicted to grow by up to 50% in the coming decades, placing both pressure on resources and heavy demands on the energy efficiency of technologies around us. The majority of primary energy consumption is wasted as heat, which is ubiquitous in a difficult-to-use low-grade form. At the same time, the number of electronic devices in both everyday life and industry is increasing rapidly. Thermoelectric materials enable converting heat into electricity, but their large-scale use is hindered by a low power per cost figure. The use of nanostructuring has enabled improving the thermoelectric performance by careful engineering of both electronic and thermal properties of these materials. Concurrently, also other material properties, such as optical transparency or mechanical flexibility, can be improved. The emergence of thermoelectric materials with functional properties could promote the widespread adoption of thermoelectric devices by providing novel uses and application domains. This thesis presents ways to engineer thermoelectric materials for functional applications using nanostructuring as well as demonstrates a few proof-of-concept devices based on these materials. The thesis first studies the thermal properties of core-shell GaAs-AlAs nanowire arrays, a material system important for a variety of optoelectronic devices. Characterization by the transient thermoreflectance technique indicates that the thickness of the introduced epitaxial AlAs shell can be exploited in controlling the thermal properties of the heterostructure. Second, widely studied transparent thermoelectric material, ZnO, is grown using atomic layer deposition (ALD). Sandwiching of Zr in between ZnO layers grown by ALD is found to improve the room-temperature thermoelectric performance of ZnO at a 2% nominal concentration of Zr. Further, nanoporous grass-like alumina (GLA) surface is used as a template for ALD of Al-doped ZnO (AZO), showing increased carrier concentration and subsequently improved electrical conductivity and thermoelectric power factor. In addition, the transparency of the AZO film grown on GLA is enhanced due to the antireflective behaviour partly inherited from GLA. Finally, nanostructured materials are used in two instances to realize flexible thermoelectric devices. First, a thermoelectric generator based on InAs nanowire networks grown directly on flexible plastic is demonstrated. Second, a thermal distribution sensor based on spray-deposited multilayer graphene is presented. The results obtained in this thesis demonstrate various ways for engineering the properties of thermoelectric materials for functional applications. Further, approaches enabling the scalable and cost-efficient fabrication of these materials are presented, drafting routes for practical utilization of functional thermoelectric devices.",

keywords = "thermoelectricity, nanostructures, thin films, l{\"a}mp{\"o}s{\"a}hk{\"o}inen ilmi{\"o}, nanorakenteet, ohutkalvot, thermoelectricity, nanostructures, thin films",

author = "Tomi Koskinen",

year = "2023",

language = "English",

isbn = "978-952-64-1374-7",

series = "Aalto University publication series DOCTORAL THESES",

publisher = "Aalto University",

number = "120",

address = "Finland",

school = "Aalto University",

}

TY - BOOK

T1 - Nanostructured thermoelectric materials for transparent and flexible applications

AU - Koskinen, Tomi

PY - 2023

Y1 - 2023

N2 - The global energy use is predicted to grow by up to 50% in the coming decades, placing both pressure on resources and heavy demands on the energy efficiency of technologies around us. The majority of primary energy consumption is wasted as heat, which is ubiquitous in a difficult-to-use low-grade form. At the same time, the number of electronic devices in both everyday life and industry is increasing rapidly. Thermoelectric materials enable converting heat into electricity, but their large-scale use is hindered by a low power per cost figure. The use of nanostructuring has enabled improving the thermoelectric performance by careful engineering of both electronic and thermal properties of these materials. Concurrently, also other material properties, such as optical transparency or mechanical flexibility, can be improved. The emergence of thermoelectric materials with functional properties could promote the widespread adoption of thermoelectric devices by providing novel uses and application domains. This thesis presents ways to engineer thermoelectric materials for functional applications using nanostructuring as well as demonstrates a few proof-of-concept devices based on these materials. The thesis first studies the thermal properties of core-shell GaAs-AlAs nanowire arrays, a material system important for a variety of optoelectronic devices. Characterization by the transient thermoreflectance technique indicates that the thickness of the introduced epitaxial AlAs shell can be exploited in controlling the thermal properties of the heterostructure. Second, widely studied transparent thermoelectric material, ZnO, is grown using atomic layer deposition (ALD). Sandwiching of Zr in between ZnO layers grown by ALD is found to improve the room-temperature thermoelectric performance of ZnO at a 2% nominal concentration of Zr. Further, nanoporous grass-like alumina (GLA) surface is used as a template for ALD of Al-doped ZnO (AZO), showing increased carrier concentration and subsequently improved electrical conductivity and thermoelectric power factor. In addition, the transparency of the AZO film grown on GLA is enhanced due to the antireflective behaviour partly inherited from GLA. Finally, nanostructured materials are used in two instances to realize flexible thermoelectric devices. First, a thermoelectric generator based on InAs nanowire networks grown directly on flexible plastic is demonstrated. Second, a thermal distribution sensor based on spray-deposited multilayer graphene is presented. The results obtained in this thesis demonstrate various ways for engineering the properties of thermoelectric materials for functional applications. Further, approaches enabling the scalable and cost-efficient fabrication of these materials are presented, drafting routes for practical utilization of functional thermoelectric devices.

AB - The global energy use is predicted to grow by up to 50% in the coming decades, placing both pressure on resources and heavy demands on the energy efficiency of technologies around us. The majority of primary energy consumption is wasted as heat, which is ubiquitous in a difficult-to-use low-grade form. At the same time, the number of electronic devices in both everyday life and industry is increasing rapidly. Thermoelectric materials enable converting heat into electricity, but their large-scale use is hindered by a low power per cost figure. The use of nanostructuring has enabled improving the thermoelectric performance by careful engineering of both electronic and thermal properties of these materials. Concurrently, also other material properties, such as optical transparency or mechanical flexibility, can be improved. The emergence of thermoelectric materials with functional properties could promote the widespread adoption of thermoelectric devices by providing novel uses and application domains. This thesis presents ways to engineer thermoelectric materials for functional applications using nanostructuring as well as demonstrates a few proof-of-concept devices based on these materials. The thesis first studies the thermal properties of core-shell GaAs-AlAs nanowire arrays, a material system important for a variety of optoelectronic devices. Characterization by the transient thermoreflectance technique indicates that the thickness of the introduced epitaxial AlAs shell can be exploited in controlling the thermal properties of the heterostructure. Second, widely studied transparent thermoelectric material, ZnO, is grown using atomic layer deposition (ALD). Sandwiching of Zr in between ZnO layers grown by ALD is found to improve the room-temperature thermoelectric performance of ZnO at a 2% nominal concentration of Zr. Further, nanoporous grass-like alumina (GLA) surface is used as a template for ALD of Al-doped ZnO (AZO), showing increased carrier concentration and subsequently improved electrical conductivity and thermoelectric power factor. In addition, the transparency of the AZO film grown on GLA is enhanced due to the antireflective behaviour partly inherited from GLA. Finally, nanostructured materials are used in two instances to realize flexible thermoelectric devices. First, a thermoelectric generator based on InAs nanowire networks grown directly on flexible plastic is demonstrated. Second, a thermal distribution sensor based on spray-deposited multilayer graphene is presented. The results obtained in this thesis demonstrate various ways for engineering the properties of thermoelectric materials for functional applications. Further, approaches enabling the scalable and cost-efficient fabrication of these materials are presented, drafting routes for practical utilization of functional thermoelectric devices.

KW - thermoelectricity

KW - nanostructures

KW - thin films

KW - lämpösähköinen ilmiö

KW - nanorakenteet

KW - ohutkalvot

KW - thermoelectricity

KW - nanostructures

KW - thin films

M3 - Doctoral Thesis

SN - 978-952-64-1374-7

T3 - Aalto University publication series DOCTORAL THESES

PB - Aalto University

ER -

Nanostructured thermoelectric materials for transparent and flexible applications

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