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Role of Oxide Defects in ALD grown TiO2 Coatings on Performance as Photoanode Protection Layer

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Role of Oxide Defects in ALD grown TiO2 Coatings on Performance as Photoanode Protection Layer. / Saari, Jesse; Ali-Löytty, Harri; Valden, Mika.

2018. Paper presented at Optics & Photonics Days 2018, Jyväskylä, Finland.

Research output: Other conference contributionPaper, poster or abstractScientific

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Saari, J, Ali-Löytty, H & Valden, M 2018, 'Role of Oxide Defects in ALD grown TiO2 Coatings on Performance as Photoanode Protection Layer' Paper presented at Optics & Photonics Days 2018, Jyväskylä, Finland, 28/05/18 - 30/05/18, .

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@conference{58d8c51c09e04e3e89c17c9a040d22da,
title = "Role of Oxide Defects in ALD grown TiO2 Coatings on Performance as Photoanode Protection Layer",
abstract = "Photoelectrochemical (PEC) water splitting is one of the potential methods of utilizing solar energy. A major issue for the method and for renewable energy production is the development of an efficient, chemically stable and cost-effective semiconductor photoanode. Recently, titanium dioxide (TiO2) coatings grown by atomic layer deposition (ALD) have appeared to be a promising approach to stabilize semiconductor photoanodes under PEC conditions. In particular, amorphous ALD grown TiO2 has shown exceptional charge transfer properties compared to its crystalline form that are not properly understood yet. Therefore, we target to gain better understanding on the defect structure of ALD grown TiO2 and utilize the information in the development of optimal photoanode protection layer for efficient solar water splitting.In this work, structural, optical and photoelectrochemical properties of the ALD grown TiO2 films were studied in as-deposited condition and after annealing in air at 500 °C. TiO2 films were grown on n-type phosphorus-doped silicon and fused quartz by ALD at 200 °C using tetrakis(dimethylamido)titanium (TDMAT) and deionized water as precursors. The properties of TiO2 were investigated by X-ray photoelectron spectroscopy (XPS), ellipsometry and UV/Vis/NIR spectrophotometry. In addition, results from X-ray diffraction (XRD), Raman spectroscopy and photoelectrochemical (PEC) cell are discussed.Based on the results, as-deposited TiO2 is amorphous and absorbs visible light as ''black'' TiO2. After annealing in air at 500 °C TiO2 crystallizes as rutile and becomes ''white'' TiO2 that absorbs light only in the UV region. As-deposited TiO2 contains significant amount of Ti3+/2+ oxygen vacancies that are oxidized as Ti4+ upon annealing in air. In addition, nitrogen is found only in as-deposited titanium dioxide. As-deposited TiO2 is not chemically stable under PEC conditions. In contrast, the annealed TiO2 is chemically stable and showed 0.20 {\%} ABPE efficiency for water splitting reaction.As a conclusion, Ti3+ defects induce photocorrosion of ALD TiO2 under PEC conditions. After annealing in air at 500 °C ALD TiO2 is chemically stable and it can be used as a photoanode protection layer. In the future, research will be focused on optimizing the properties of ALD TiO2/Si interface and studying the structure of the surface after deposition of nickel electrocatalysts on TiO2/Si photoanode.",
keywords = "Atomic layer deposition, Titanium dioxide, Photoelectrochemical water splitting",
author = "Jesse Saari and Harri Ali-L{\"o}ytty and Mika Valden",
year = "2018",
month = "5",
day = "29",
language = "English",
note = "Optics & Photonics Days 2018 ; Conference date: 28-05-2018 Through 30-05-2018",

}

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TY - CONF

T1 - Role of Oxide Defects in ALD grown TiO2 Coatings on Performance as Photoanode Protection Layer

AU - Saari, Jesse

AU - Ali-Löytty, Harri

AU - Valden, Mika

PY - 2018/5/29

Y1 - 2018/5/29

N2 - Photoelectrochemical (PEC) water splitting is one of the potential methods of utilizing solar energy. A major issue for the method and for renewable energy production is the development of an efficient, chemically stable and cost-effective semiconductor photoanode. Recently, titanium dioxide (TiO2) coatings grown by atomic layer deposition (ALD) have appeared to be a promising approach to stabilize semiconductor photoanodes under PEC conditions. In particular, amorphous ALD grown TiO2 has shown exceptional charge transfer properties compared to its crystalline form that are not properly understood yet. Therefore, we target to gain better understanding on the defect structure of ALD grown TiO2 and utilize the information in the development of optimal photoanode protection layer for efficient solar water splitting.In this work, structural, optical and photoelectrochemical properties of the ALD grown TiO2 films were studied in as-deposited condition and after annealing in air at 500 °C. TiO2 films were grown on n-type phosphorus-doped silicon and fused quartz by ALD at 200 °C using tetrakis(dimethylamido)titanium (TDMAT) and deionized water as precursors. The properties of TiO2 were investigated by X-ray photoelectron spectroscopy (XPS), ellipsometry and UV/Vis/NIR spectrophotometry. In addition, results from X-ray diffraction (XRD), Raman spectroscopy and photoelectrochemical (PEC) cell are discussed.Based on the results, as-deposited TiO2 is amorphous and absorbs visible light as ''black'' TiO2. After annealing in air at 500 °C TiO2 crystallizes as rutile and becomes ''white'' TiO2 that absorbs light only in the UV region. As-deposited TiO2 contains significant amount of Ti3+/2+ oxygen vacancies that are oxidized as Ti4+ upon annealing in air. In addition, nitrogen is found only in as-deposited titanium dioxide. As-deposited TiO2 is not chemically stable under PEC conditions. In contrast, the annealed TiO2 is chemically stable and showed 0.20 % ABPE efficiency for water splitting reaction.As a conclusion, Ti3+ defects induce photocorrosion of ALD TiO2 under PEC conditions. After annealing in air at 500 °C ALD TiO2 is chemically stable and it can be used as a photoanode protection layer. In the future, research will be focused on optimizing the properties of ALD TiO2/Si interface and studying the structure of the surface after deposition of nickel electrocatalysts on TiO2/Si photoanode.

AB - Photoelectrochemical (PEC) water splitting is one of the potential methods of utilizing solar energy. A major issue for the method and for renewable energy production is the development of an efficient, chemically stable and cost-effective semiconductor photoanode. Recently, titanium dioxide (TiO2) coatings grown by atomic layer deposition (ALD) have appeared to be a promising approach to stabilize semiconductor photoanodes under PEC conditions. In particular, amorphous ALD grown TiO2 has shown exceptional charge transfer properties compared to its crystalline form that are not properly understood yet. Therefore, we target to gain better understanding on the defect structure of ALD grown TiO2 and utilize the information in the development of optimal photoanode protection layer for efficient solar water splitting.In this work, structural, optical and photoelectrochemical properties of the ALD grown TiO2 films were studied in as-deposited condition and after annealing in air at 500 °C. TiO2 films were grown on n-type phosphorus-doped silicon and fused quartz by ALD at 200 °C using tetrakis(dimethylamido)titanium (TDMAT) and deionized water as precursors. The properties of TiO2 were investigated by X-ray photoelectron spectroscopy (XPS), ellipsometry and UV/Vis/NIR spectrophotometry. In addition, results from X-ray diffraction (XRD), Raman spectroscopy and photoelectrochemical (PEC) cell are discussed.Based on the results, as-deposited TiO2 is amorphous and absorbs visible light as ''black'' TiO2. After annealing in air at 500 °C TiO2 crystallizes as rutile and becomes ''white'' TiO2 that absorbs light only in the UV region. As-deposited TiO2 contains significant amount of Ti3+/2+ oxygen vacancies that are oxidized as Ti4+ upon annealing in air. In addition, nitrogen is found only in as-deposited titanium dioxide. As-deposited TiO2 is not chemically stable under PEC conditions. In contrast, the annealed TiO2 is chemically stable and showed 0.20 % ABPE efficiency for water splitting reaction.As a conclusion, Ti3+ defects induce photocorrosion of ALD TiO2 under PEC conditions. After annealing in air at 500 °C ALD TiO2 is chemically stable and it can be used as a photoanode protection layer. In the future, research will be focused on optimizing the properties of ALD TiO2/Si interface and studying the structure of the surface after deposition of nickel electrocatalysts on TiO2/Si photoanode.

KW - Atomic layer deposition

KW - Titanium dioxide

KW - Photoelectrochemical water splitting

M3 - Paper, poster or abstract

ER -