Effect of Defect on the Photoelectrochemical Performance of Amorphous ALD-TiO x Thin Films = 결함이 비정질 ALD-TiO x 박막의 광전기 화학적 성능에 미치는 영향

다국어 초록 (Multilingual Abstract)

The unchecked use of fossil fuels is accelerating global warming due to the greenhouse effect. Finding new technologies to harvest energy from renewable sources is crucial for a sustainable civilization. One promising alternative is generating hydrogen fuel from solar energy and water via the photoelectrochemical (PEC) water splitting process. Titanium dioxide (TiO2) has been a promising material for PEC applications for several decades, especially defective TiO2 has shown higher PEC performance due to its excellent chemical and electrical properties.
In this study, we used atomic layer deposition (ALD) with TDMAT as a precursor for Ti to deposit amorphous titanium oxide (TiOx) films on both Si wafers and FTO-coated glass substrates. We performed focused ion beam (FIB) studies with Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) cross-sections to verify the thickness and defect concentration of small ALD-TiOx film layers within the TiOx film matrix.
Additionally, we evaluated the film's optical absorption properties by conducting UV-Vis absorption spectroscopy. The defect concentration of the TiOx film was
adjusted by changing the chamber temperature during the ALD process. The TiOx film deposited at 200 °C showed a higher defect concentration than other films, resulting in a higher photo absorption efficiency (~50.41 %), photo-generated charge separation efficiency (~33.31 % at 1.23 V vs. RHE), and charge transfer efficiency (~80.33 % at 1.23 V vs. RHE), and a photocurrent density of 0.051 mA/cm2 at 1.23 V vs. RHE. Finally, we systematically correlated the defect concentration of the amorphous TiOx film with its PEC activity. This study provides insights into the detailed PEC characteristics of the defective amorphous ALD-TiOx films.

목차 (Table of Contents)

• Contents ·························································································································· ⅰ
• LIST of TABLES ············································································································ ⅲ
• LIST of FIGURES ·········································································································· ⅳ
• Abstract ··························································································································· ⅷ
• 1. Introduction ················································································································ 1
• 2. Theoretical background ·························································································· 7
• 2-1. Overview of Photoelectrochemical ······························································ 7
• 2-1-1. Photoelectrochemical water splitting ················································· 7
• 2-1-2. Reversible hydrogen electrode ··························································· 11
• 2-1-3. Photoanode Materials ············································································ 13
• 2-2. TiO 2 materials ·································································································· 14
• 2-2-1. Properties of TiO 2 ··················································································· 14
• 2-2-2. Photocatalytic Reaction ········································································· 19
• 2-2-3. Doping and visible light utilization of TiO 2 ···································· 23
• 2-3. The Basic Principles of Atomic Layer Deposition ······························· 28
• 2-3-1. Atomic Layer Deposition ······································································ 28
• 2-3-2. Characteristics of Atomic Layer Deposition ·································· 33
• 2-4. Measuring Instrument Principles ······························································ 36
• 2-4-1. X-ray diffraction ······················································································ 36
• 2-4-2. Transmission Electron Microscope ··················································· 39
• 2-4-3. X-ray Photoelectron Spectroscopy ···················································· 42
• 2-4-4. Electron Spin Resonance ····································································· 42
• 2-4-5. UV-Vis Spectrophotometer ································································· 47
• 2-5. Electrochemical Analysis Methods ···························································· 48
• 2-5-1. Linear Sweep Voltammetry ································································· 48
• 2-5-2. Chronoamperometry ··············································································· 49
• 2-5-3. Applied bias photon-to-current efficiency ······································ 50
• 2-5-4. Electrochemical Impedance Spectroscopy ······································ 52
• 3. Experiment details ································································································· 54
• 3-1. Deposition conditions for TiO x thin film ················································· 54
• 3-2. Characterization of TiO x thin film ····························································· 58
• 3-3. Evaluation of photoelectrochemical water degradation properties of TiO x thin film photoanodes ··············· 59
• 4. Results and discussion ························································································· 62
• 4-1. ALD growth characteristics of TiO x thin films · 62
• 4-2. Structural Characteristics of TiO x Thin Films ······································· 67
• 4-2-1. Crystallinity and Structural Analysis of TiO x ·································· 67
• 4-3. Chemical properties of TiO x thin films ···················································· 69
• 4-3-1. Bonding analysis of TiO x via XPS ····················································· 69
• 4-3-2. Bonding analysis of TiO x via ESR ····················································· 74
• 4-4. Evaluation of photoelectrochemical properties of TiO x thin films · 76
• 4-4-1. Evaluation of photocatalytic activity and photoconversion efficiency of TiO x thin films ··························· 76
• 4-5. Factorial study of theoretical photocurrent for water splitting of TiO x thin films ······································· 80
• 4-5-1. Analysis of absorption and photon harvesting efficiency of TiO x thin films ································ 80
• 4-5-2. Evaluation of charge absorption properties of TiO x thin films 83
• 4-5-3. Evaluation of Charge Separation Properties of TiO x Thin Films 87
• 4-5-4. Evaluation of charge absorption characteristics of TiO x thin films ······ 92
• 4-5-5. Durability evaluation ·············································································· 94
• 5. Conclusion ················································································································· 96
• 6. Reference ·················································································································· 98
• Abstract (Korean) ······································································································ 108