Synthesis of Perovskite Nanocrystal Using Liquid Crystal and Application to Optoelectronic Device|RISS 상세보기

다국어 초록 (Multilingual Abstract)

This dissertation investigates the innovative utilization of liquid crystals in the synthesis of perovskite nanocrystals, exploring their potential to enhance the control of nanocrystal morphology, stability, and the optoelectronic properties. This research is motivated by the need for precise morphological control and enhanced stability in perovskite nanocrystals, which are critical for advancing their application in optoelectronic devices. The primary objective of this study is to elucidate the uniform synthesis and growth mechanisms of rod-shaped perovskite nanocrystals using liquid crystals as a template and to assess their impact on the optical properties of nanocrystals post-ligand exchange processes. Liquid crystals offer a strategic approach due to their elasticity and orientation, acting as templates during the synthesis of nanocrystals. This allows for the uniform synthesis of nanocrystals with targeted morphologies. The presence of liquid crystals during the synthesis process enables advanced analytical and quantitative analysis through their optical polarization phenomena. The methodology adopted involves the liquid crystal-assisted synthesis of perovskite nanocrystals, focusing on rod-shaped morphologies. Utilizing liquid crystals as a template not only aids in achieving the desired morphology, but also improves the stability of nanocrystals during ligand exchange processes. This research introduces a novel chemical transformation approach using liquid crystal templates to develop precise synthesis methodologies. The influence of liquid crystals on the surface of nanocrystals during post-ligand exchange processes is critically evaluated to understand their impact on optical and optoelectronic properties of the nanocrystals. The final chapters discuss the successful synthesis of bismuth-based perovskite nanocrystals using the liquid crystal method and a machine learning optimization approach to overcome the lead toxicity challenge. These techniques enhance predictive modeling for achieving desired outcomes and developing lead-free perovskite nanocrystals. This research contributes to the field of materials science by offering viable solutions for the commercialization of perovskite nanocrystals in optoelectronic applications and highlights innovative methods to address environmental and stability concerns associated with these materials.

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목차 (Table of Contents)

Abstract i
Table of Contents iii
List of Figures viii
List of Tables xvi
Chapter 1. Introduction 1

Abstract i
Table of Contents iii
List of Figures viii
List of Tables xvi
Chapter 1. Introduction 1
1.1. Perovskite Nanocrystals for Light-emitting device 1
1.2. Challenges of Perovskite Nanocrystals 3
1.3. Motivation and Objectives 5
1.4. Thesis Outline 6
1.5. Reference 7
Chapter 2. Background and theory 10
2.1. Perovskites Nanocrystals 10
2.1.1. Crystal Structure 10
2.1.2. Synthesis Method; Hot Injection 11
2.1.3. Synthesis Method; Ligand-assisted Reprecipitation (LARP) 12
2.1.4. Synthesis Method; Microwave-assisted and Solvothermal 14
2.2. Perovskite nanocrystal-based LEDs 15
2.2.1. Device Configurations 15
2.2.2. Operation Principles 17
2.2.3. Key Parameters of LEDs 19
iv
2.3. Literature Review: Application for Perovskite Nanocrystal-Based LEDs 23
2.3.1. Nanorod and Synthesis method 23
2.3.2. Ligand Exchange 27
2.3.3. Lead Substitution 29
2.4. Reference 31
Chapter 3. Synthesis of Perovskite Nanorod Using Liquid Crystal Template .. 35
3.1. Introduction 35
3.2. Mechanism of Liquid Crystal Template 37
3.3. Precise Control of Growth with Morphology Characterization 39
3.4. Identification of Chemical Transformation 42
3.5. Optoelectrical Properties Characterization of CsPbBr3 Nanocrystals 43
3.6. Mechanism Demonstration of Chemical Transformation 46
3.7. Mechanism Demonstration of Anisotropic Growth 50
3.8. Conclusion 53
3.9. Experimental 55
3.9.1. Materials 55
3.9.2. Preparation of Cs4PbBr6 Seeds 55
3.9.3. Preparation of Liquid Crystal Template 56
3.9.4. Synthesis of CsPbBr3 Nanorods using Liquid Crystal Template 56
3.9.5. Synthesis of CsPbBr3 Nanorods using Conventional Method 56
3.9.6. Fabrication of CsPbBr3 Nanocrystal-based LEDs 57
v
3.9.7. Characterization of Perovskite Nanocrystals 57
3.9.8. Characterization of LED Performance 58
3.9.9. Mechanism Analysis of Chemical Transformation 59
3.9.10. Calculation of Surface Tension Energy of Different Location 59
3.9.11. Calculation of Exact location of Cs4PbBr6 Seed 61
3.9.12. Calculation of Exact Position of Cs4PbBr6 Seed 62
3.9.13. Calculation of Growth Direction of CsPbBr3 Nanocrystal 64
3.10. Reference 66
Chapter 4. Ligand Exchange Using Liquid Crystal 69
4.1. Introduction 69
4.2. Mechanism of Liquid Crystal-assisted Ligand Exchange 71
4.3. Morphology Characterization using TEM Analysis. 73
4.4. Materials and Optical Characterization using XRD, FT-IR, UV-PL 74
4.5. Effect Characterization of Liquid Crystal-Ligand Exchange 77
4.6. Optical and Stability Characterization 79
4.7. Materials Characterization using XPS 82
4.8. Stability Test 84
4.9. Device Characterization 87
4.10 Conclusion 89
4.11. Experimental 91
4.11.1. Materials 91
4.11.2. Synthesis of CsPbBr3 Nanocrystals via LARP. 91
vi
4.11.3. Ligand Exchange of Pre-synthesized CsPbBr3 Nanocrystals 92
4.11.4. Device Fabrication 92
4.11.5. Characterizations of CsPbBr3 Nanocrystals 93
4.11.6. Characterizations of CsPbBr3 Nanocrystal-based LEDs 94
4.12. Reference 94
Chapter 5. Lead-free and Optimization for Future Application 98
5.1. Introduction 98
5.2. Synthesis of Lead-free Perovskite Nanocrystals Using Liquid Crystal 101
5.3. A-site Mixing 102
5.4. Modeling 104
5.5. Toward Machine Learning 106
5.6. Suggestion Machine Learning 109
5.7. Conclusion 112
5.8. Experimental 113
5.8.1. Materials 113
5.8.2. Synthesis of Lead-free Perovskite Nanocrystals (Cs3BiBr6) 113
5.8.3. Synthesis of A-site Mixed Perovskite Nanocrystals 114
5.8.4. Natural Neighboring Interpolation Toward Machine Learning 114
5.8.5. Characterization of Machine Learning Model 115
5.8.6. Characterization of Optical Properties of Perovskite Nanocrystals 117
5.8.7. Methodology of Performance Factor 118
5.8.8. Maximum Peak Wavelength 118
vii
5.8.9. Half-Width at Half-Maximum (HWHM) 118
5.8.10. Mean-Median Metric 119
5.8.11. Normalization and Symmetric Index Calculation 119
5.8.12. Performance Metric Calculation 120
5.9. Reference 120
Summary and Conclusion 123
Summary in Korean. 125
Acknowledgements 128
Curriculum Vitae 134

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