Zwitterionic ligand engineering of perovskite nanocrystals for high-resolution patterning and photocatalytic applications

다국어 초록 (Multilingual Abstract)

With the global increase in energy demand and growing environmental concerns, the development of sustainable, efficient, and environmentally friendly energy production technologies has become paramount. Colloidal nanocrystals have emerged as highly promising materials for various applications, including energy conversion and storage, catalysis, and optoelectronics. Their high surface area, tunable size, and surfactant modulation capabilities enable customization of their properties, facilitating the modification of intrinsic characteristics and the introduction of new functionalities. Among nanocrystals, perovskite nanocrystals (PNCs) have attracted significant attention as next-generation semiconductors due to their outstanding electrical and optical properties. PNCs possess desirable attributes such as low material cost, broad absorption spectrum, high extinction coefficient, high charge carrier mobility, tunable bandgap, high photoluminescence quantum yield (PLQY), and narrow emission linewidth, making them ideal candidates for applications in solar cells, light-emitting diodes (LEDs), photodetectors, lasers, and photocatalysis. However, the practical industrial application of PNCs faces challenges due to their inherent instability. This instability primarily stems from the soft crystal structure of PNCs and the desorption of surface ligands, leading to defect formation, degradation of optical properties, and material degradation. Moreover, PNCs exhibit high reactivity and are highly sensitive to ambient environmental conditions, such as oxygen and water vapor. This dissertation focuses on the study of utilizing zwitterionic molecules with intrinsic dipoles as stabilizing ligands for PNCs, aiming to enhance their stability and introduce novel functionalities for energy conversion applications.
Chapter 1 introduces the basic concepts of colloidal nanocrystals and discusses their various application possibilities. It specifically introduces the features and research status of PNCs, and explores the fundamental reasons that enable their outstanding properties. Various synthesis methods of nanocrystals are categorized into top-down and bottom-up approaches, and by comparing them, the importance of solution process-based synthesis is emphasized. The strengths and weaknesses of the hot injection method are discussed in detail, and the postsynthesis ligand exchange (PSLE) process is proposed as a promising alternative to resolve the washing step, an essential process of the hot injection method. The characteristics and research trends of zwitterionic ligands, which can significantly improve the stability of PNCs, are explained.
Chapter 2 introduces research on enhancing the stability of PNCs through the PSLE process using zwitterionic sulfobetaine (ZSB) ligands and improvingphotocatalytic properties by leveraging the unique dipole characteristics of ZSB ligands. We detail how the problem of low solubility of ZSB ligands in organic solvents was solved by long-term ligand substitution based on PSLE, and how this improved the properties and stability of PNCs. A novel discovery about the bonding structure of ZSB ligands, depending on the elemental composition of the PNC surface, is also presented. Finally, we will show how to make composites with the co-catalyst titanium oxide (Pt-TiO2) for hydrogen production and further improve the performance and stability of these composites.
Chapter 3 introduces new photocrosslinkable zwitterionic (PZ) ligands optimized for the PSLE process and provides an in-depth discussion of the modified PSLE process. we demonstrate the improved ligand exchange mechanism through comprehensive surface analysis and introduce the enhanced optical properties, stability, and dispersibility in polar solvents of PNCs. We then describe a direct photopatterning process developed by utilizing the properties of the PZ ligand and the high photoreactivity of PNCs. Well-ordered, pinhole-free, and uniform PNC films made by inducing electrostatic interactions through the intrinsic dipole of the PZ ligand are presented. We also show that this improved film quality enables highresolution direct photopatterning.

목차 (Table of Contents)

• List of Figures ⅰⅴ
• List of Tables . ⅹⅰⅰⅰ
• List of Abstract . ⅹⅰⅴ
• Chapter 1. Introduction
• 1.1. Colloidal nanocrystals for energy conversion devices 1
• 1.2. Next-generation semiconductor materials for optoelectronic devices: Perovskite nanocrystals (PNCs) 5
• 1.2.1. Introduction of PNCs 5
• 1.2.2. Colloidal synthesis methods 11
• 1.2.3. Solution phase synthesis: Hot-injection method 15
• 1.2.4. Post-synthetic ligand exchange 18
• 1.3. References 20
• Chapter 2. Monodentate Binding of Zwitterionic Ligands for Boosting Photocatalytic H2 Production of Perovskite Nanocrystals
• 2.1. Introduction 22
• 2.2. Experimental methods 25
• 2.2.1. Materials 25
• 2.2.2. Synthesis of CsPbBr3 PNCs and ligand exchange methods 25
• 2.2.3. Preparation of Pt-TiO2 and Pt-TiO2/CsPbBr3 PNC composites 27
• 2.2.4. Preparation of CsPbBr3-saturated HBr solutions 27
• 2.2.5. Photocatalytic H2 production 28
• 2.2.6. Computational Calculation 28
• 2.2.7. Other measurements and characterization 29
• 2.3. Results and Discussion 30
• 2.4. Conclusion . 69
• 2.5. References 70
• Chapter 3. Photocrosslinkable Zwitterionic Ligands for Perovskite Nanocrystals: Self-Assembly and High-Resolution Direct patterning
• 3.1. Introduction 73
• 3.2. Experimental Methods 75
• 3.2.1. Materials 75
• 3.2.2. Synthesis of CsPbBr3 PNCs and ligand exchange methods 76
• 3.2.3. Direct photopatterning procedure 77
• 3.2.4. Synthesis of photocrosslinkable zwitterionic (PZ) ligand 78
• 3.2.5. Measurements and Characterization 80
• 3.2.6. Computational Calculations . 81
• 3.3. Results and Discussion 82
• 3.4. Conclusion 135
• 3.5. References 136
• List of Publications 138
• 국문요지 . 140
• Acknowledgement . 142