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Pulsed Laser Deposition of Efficient Ternary Metal Oxide Photoelectrodes = = Gepulste Laserabscheidung von effizienten ternaren Metalloxid-Photoelektroden /

Record Type:	Electronic resources : Monograph/item
Title/Author:	Pulsed Laser Deposition of Efficient Ternary Metal Oxide Photoelectrodes =/ Moritz Kolbach.
Reminder of title:	Gepulste Laserabscheidung von effizienten ternaren Metalloxid-Photoelektroden /
Author:	Kolbach, Moritz,
Description:	1 electronic resource (137 pages)
Notes:	Source: Dissertations Abstracts International, Volume: 82-01, Section: B.
Contained By:	Dissertations Abstracts International82-01B.
Subject:	Condensed matter physics. -
Online resource:	https://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=27605504
ISBN:	9781687916075

Pulsed Laser Deposition of Efficient Ternary Metal Oxide Photoelectrodes = = Gepulste Laserabscheidung von effizienten ternaren Metalloxid-Photoelektroden /
Kolbach, Moritz,

Pulsed Laser Deposition of Efficient Ternary Metal Oxide Photoelectrodes =Gepulste Laserabscheidung von effizienten ternaren Metalloxid-Photoelektroden /Moritz Kolbach. - 1 electronic resource (137 pages)

Source: Dissertations Abstracts International, Volume: 82-01, Section: B.

Climate change, mainly driven by the combustion of fossil fuels releasing the greenhouse gas CO2, is a major threat to humanity and the ecosystems on our planet. To limit global warming, a transition towards a sustainable energy infrastructure based on renewable energies is essential. The storage of solar energy in the form of chemical bonds, in so-called solar fuels, is thereby believed to be a key technology. This approach solves the problem of the intermittent nature of solar power-the only renewable energy source capable of meeting the still growing world energy demand on a TW scale. One possible pathway towards solar fuels is the generation of hydrogen via photoelectrochemical (PEC) water splitting using semiconducting photoelectrodes immersed in an aqueous electrolyte. However, the material that meets all the stringent requirements for efficient and commercially viable solar water splitting is still elusive. Metal oxides are a promising class of photoelectrode materials because they are in general cheaper and more stable in aqueous solutions than conventional III-V semiconductors. Since only few-if any-of the simple binary oxides show the desired properties, recent efforts in the field have shifted towards investigating the more complex multinary oxides. To study the fundamental properties and performance limitations of such novel photoelectrode materials, one needs to be able to deposit thin and compact films of high electronic quality. Pulsed laser deposition (PLD) is a versatile physical vapor deposition technique that meets these demands. Therefore, in this thesis, this powerful tool is used to (i) deposit dense and high-quality BiVO4 photoelectrodes and (ii) to comprehensively evaluate the new and promising material a-SnWO4. In the first part, the complex PLD process of BiVO4 films by ablating a BiVO4 target is systematically elucidated with a special focus on the deviations from an ideal stoichiometric target-to-substrate transfer. By correlating the V:Bi ratio of the films with their charge carrier transport properties and PEC performance, remarkable AM1.5 sulfite oxidation photocurrents of 2.4 ± 0.2 mAcm-2 at E = 1.23 V vs. RHE with stoichiometric films are achieved without any doping or nanostructuring. BiVO4 photoelectrodes with similar PEC performance are additionally prepared for the first time by the alternating ablation of Bi2O3 and V2O5 targets. This approach is shown to be an attractive alternative route to control the cation stoichiometry and lays the foundation for the future growth of epitaxial BiVO4 films. The second part of this thesis contains a comprehensive evaluation of a-SnWO4 as a novel photoelectrode material. a-SnWO4 has recently attracted attention in the field due to the combination of a nearly ideal bandgap (~1.9 eV) and a very early photocurrent onset potential (~0 V vs. RHE). Using phase-pure pulsed laser deposited films, the close-tooptimum band alignment and bandgap is confirmed, and other important parameters such as the charge carrier mobility, lifetime, diffusion length, and the PEC stability are reported for the first time. A high-temperature treatment is shown to enhance the charge carrier mobility of a- SnWO4 films by more than two orders of magnitude, as measured with time-resolved microwave conductivity (TRMC). This results in one of the highest effective charge carrier diffusion lengths ever measured in a metal oxide photoelectrode (~200 nm). A complimentary analysis by time-resolved terahertz spectroscopy (TRTS) shows that this improvement can be attributed to larger grain/domain sizes with increasing heat-treatment temperature. In other words, grain boundaries significantly limit the charge carrier transport in a-SnWO4. In addition, a hole-conductive NiOx protection layer is introduced to prevent self-passivation of the surface of the a-SnWO4 films (formation of a thin SnO2 layer), which drastically increases the sulfite oxidation photocurrent by a factor of ~100 setting a new benchmark AM1.5 photocurrent density (~0.75 mA cm-2 at E = 1.23 V vs. RHE) and IPCE (~38% at λ = 355 nm) for a-SnWO4. These findings provide important insights into the key PEC properties and performance limitations of a-SnWO4, and allow the identification of strategies to further improve the performance of this promising photoanode material.

English

ISBN: 9781687916075Subjects--Topical Terms:

3173567
Condensed matter physics.
Subjects--Index Terms:

Photoelectrodes

Pulsed Laser Deposition of Efficient Ternary Metal Oxide Photoelectrodes = = Gepulste Laserabscheidung von effizienten ternaren Metalloxid-Photoelektroden /
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245 1 0 $a Pulsed Laser Deposition of Efficient Ternary Metal Oxide Photoelectrodes = $b Gepulste Laserabscheidung von effizienten ternaren Metalloxid-Photoelektroden / $c Moritz Kolbach.
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500 $a Source: Dissertations Abstracts International, Volume: 82-01, Section: B.
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520 $a Climate change, mainly driven by the combustion of fossil fuels releasing the greenhouse gas CO2, is a major threat to humanity and the ecosystems on our planet. To limit global warming, a transition towards a sustainable energy infrastructure based on renewable energies is essential. The storage of solar energy in the form of chemical bonds, in so-called solar fuels, is thereby believed to be a key technology. This approach solves the problem of the intermittent nature of solar power-the only renewable energy source capable of meeting the still growing world energy demand on a TW scale. One possible pathway towards solar fuels is the generation of hydrogen via photoelectrochemical (PEC) water splitting using semiconducting photoelectrodes immersed in an aqueous electrolyte. However, the material that meets all the stringent requirements for efficient and commercially viable solar water splitting is still elusive. Metal oxides are a promising class of photoelectrode materials because they are in general cheaper and more stable in aqueous solutions than conventional III-V semiconductors. Since only few-if any-of the simple binary oxides show the desired properties, recent efforts in the field have shifted towards investigating the more complex multinary oxides. To study the fundamental properties and performance limitations of such novel photoelectrode materials, one needs to be able to deposit thin and compact films of high electronic quality. Pulsed laser deposition (PLD) is a versatile physical vapor deposition technique that meets these demands. Therefore, in this thesis, this powerful tool is used to (i) deposit dense and high-quality BiVO4 photoelectrodes and (ii) to comprehensively evaluate the new and promising material a-SnWO4. In the first part, the complex PLD process of BiVO4 films by ablating a BiVO4 target is systematically elucidated with a special focus on the deviations from an ideal stoichiometric target-to-substrate transfer. By correlating the V:Bi ratio of the films with their charge carrier transport properties and PEC performance, remarkable AM1.5 sulfite oxidation photocurrents of 2.4 ± 0.2 mAcm-2 at E = 1.23 V vs. RHE with stoichiometric films are achieved without any doping or nanostructuring. BiVO4 photoelectrodes with similar PEC performance are additionally prepared for the first time by the alternating ablation of Bi2O3 and V2O5 targets. This approach is shown to be an attractive alternative route to control the cation stoichiometry and lays the foundation for the future growth of epitaxial BiVO4 films. The second part of this thesis contains a comprehensive evaluation of a-SnWO4 as a novel photoelectrode material. a-SnWO4 has recently attracted attention in the field due to the combination of a nearly ideal bandgap (~1.9 eV) and a very early photocurrent onset potential (~0 V vs. RHE). Using phase-pure pulsed laser deposited films, the close-tooptimum band alignment and bandgap is confirmed, and other important parameters such as the charge carrier mobility, lifetime, diffusion length, and the PEC stability are reported for the first time. A high-temperature treatment is shown to enhance the charge carrier mobility of a- SnWO4 films by more than two orders of magnitude, as measured with time-resolved microwave conductivity (TRMC). This results in one of the highest effective charge carrier diffusion lengths ever measured in a metal oxide photoelectrode (~200 nm). A complimentary analysis by time-resolved terahertz spectroscopy (TRTS) shows that this improvement can be attributed to larger grain/domain sizes with increasing heat-treatment temperature. In other words, grain boundaries significantly limit the charge carrier transport in a-SnWO4. In addition, a hole-conductive NiOx protection layer is introduced to prevent self-passivation of the surface of the a-SnWO4 films (formation of a thin SnO2 layer), which drastically increases the sulfite oxidation photocurrent by a factor of ~100 setting a new benchmark AM1.5 photocurrent density (~0.75 mA cm-2 at E = 1.23 V vs. RHE) and IPCE (~38% at λ = 355 nm) for a-SnWO4. These findings provide important insights into the key PEC properties and performance limitations of a-SnWO4, and allow the identification of strategies to further improve the performance of this promising photoanode material.
520 $a Der Klimawandel, welcher hauptsachlich durch die Verbrennung fossiler Brennstoffe zur Energiegewinnung und den daraus resultierenden Emissionen des Treibhausgases CO2 vorangetrieben wird, ist eine immense Bedrohung fur die Menschheit und Okosysteme unserer Erde. Um die globale Erwarmung zu begrenzen, ist ein Ubergang von fossilen zu erneuerbaren Energien essentiell. Dabei wird der Speicherung von solarer Energie in Form von chemischen Bindungen in sogenannten solaren Brennstoffen eine bedeutende Rolle zugeschrieben. Dieses an die Photosynthese in Pflanzen angelehnte Konzept lost das Problem der diskontinuierlich verfugbaren Solarenergie, welche unverzichtbar ist um den stetig wachsenden Weltenergiebedarf auf einer TW-Skala zu decken. Eine Moglichkeit solare Brennstoffe herzustellen ist die Produktion von Wasserstoff mittels photoelektrochemischer Wasserspaltung mit Hilfe von in wassrigen Losungen eintauchenden halbleitenden Photoelektroden. Das Photoelektrodenmaterial, das alle strikten Anforderungen erfullt um hoch-effizient und wirtschaftlich Wasserstoff zu erzeugen, wurde jedoch noch nicht gefunden. Metalloxide stellen eine vielversprechende Materialklasse fur Photoelektroden dar, weil sie generell gunstiger und stabiler sind als konventionelle III-V Halbleiter. Da nur wenige der binaren Oxide geeignete Eigenschaften besitzen, werden in diesem Forschungsfeld nun auch komplexere multinare Oxide untersucht. Um die fundamentalen Eigenschaften und limitierenden Faktoren zu erforschen, werden kompakte Filme von hoher elektronischer Qualitat benotigt. Die gepulste Laserabscheidung ("pulsed laser deposition", PLD) ist ein vielseitiges physikalisches Gasphasenabscheidungs-Verfahren, das diese Anforderungen erfullt. Daher wird es in dieser Arbeit genutzt, um zum einen (i) kompakte und qualitativ hochwertige BiVO4 Photoelektroden abzuscheiden und zum anderen (ii) das neue und vielversprechende Material a-SnWO4 umfassend zu untersuchen. Im ersten Teil dieser Arbeit wird der komplexe gepulste Laserabscheidungsprozess von BiVO4 Filmen mittels Ablation eines BiVO4 Targets systematisch mit besonderem Hinblick auf Abweichungen von einem idealen stochiometrischen Target-zu-Substrat Transfer untersucht. Dabei wird das V:Bi Verhaltnis der Filme mit deren Ladungstragertransport und photoelektrochemischen Aktivitat korreliert und so ohne jegliche Dotierung oder Nanostrukturierung relativ hohe AM1.5 Photostrome mit stochiometrischen Filmen erzielt (2.4 ± 0.2 mAcm-2 bei E = 1.23 V vs. RHE mit Na2SO3 als Lochfanger). Daruber hinaus werden BiVO4 Photoelektroden mit einer ahnlich hohen Photoaktivitat zum ersten Mal durch die alternierende Ablation von Bi2O3 und V2O5 Targets hergestellt. Dieser Ansatz stellt sich als eleganter alternativer Weg heraus, die kationische Stochiometrie von Metalloxiden zu kontrollieren und legt die Grundlage fur das zukunftige Abscheiden von epitaktischen Schichten. Im zweiten Teil der Arbeit wird a-SnWO4 ausfuhrlich als Photoelektrodenmaterial evaluiert. Dieses Material erregte Aufmerksamkeit aufgrund seiner nahezu idealen Bandlucke (~1.9 eV) und seines bei sehr negativen Potentialen einsetzenden Photostroms (~0 V vs. RHE). Mittels gepulster Laserabscheidung hergestellte a-SnWO4 Filme werden benutzt, um die schon in der Literatur bekannte Bandanordnung und -lucke zu bestatigen und zum ersten Mal weitere essentielle Eigenschaften wie die Mobilitat, Lebensdauer und Diffusionslange der Ladungstrager sowie die photoelektrochemische Stabilitat zu untersuchen. Es wird gezeigt, dass die mittels zeit-aufgeloster Mikrowellen Spektroskopie gemessene Ladungstragermobilitat durch eine Hochtemperatur-Behandlung der Schichten um mehr als zwei Grosenordnungen erhoht werden kann. Daraus ergibt sich fur a-SnWO4 eine der grosten je gemessenen Diffusionslangen in Metalloxid Photoelektroden (~200 nm). Eine erganzende Analyse mittels zeit-aufgeloster Terahertz Spektroskopie zeigt, dass diese Verbesserung auf grosere Korngrosen in den hochtemperaturbehandelten Schichten zuruckgefuhrt werden kann und liefert die wichtige Erkenntnis, dass Korngrenzen den Ladungstransport in a-SnWO4 limitieren. Zusatzlich wird eine lochleitende NiOx Schutzschicht auf die a-SnWO4 Filme aufgetragen, die die Selbstpassivierung (Oxidation der Oberflache zu SnO2) verhindert. Dadurch wird der Photostrom (mit Na2SO3 als Lochfanger) um einen Faktor von ~100 erhoht und so neue Masstabe fur den AM1.5 Photostrom (~0.75 mA cm-2 bei E = 1.23 V vs. RHE) und die Quanteneffizienz (~38% bei λ = 355 nm) fur dieses Material gesetzt. Diese Ergebnisse liefern wichtige Erkenntnisse uber Schlussel-Parameter von a-SnWO4 und zeigen Strategien auf, die Performance von diesem vielversprechenden Photoelektrodenmaterial weiter zu verbessern.
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653 $a Photoelectrodes
653 $a Bismuth oxides
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