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Study on Inorganic Halide Perovskite Quantum Dots for Improved Stability: Their Application for Display

초록/요약

The main purpose of this paper is to introduce the chemical theory and synthesis method for the surface and structure stabilization of perovskite quantum dots (PeQDs) as well as its synthesis methods and their applications, including color filtering and electroluminescence for display. Perovskite quantum dots boast an easy synthesis method and high efficiency. It is a nanomaterial field that has grown rapidly based on expanding know-how related to quantum dots such as InP, PbS CdSe, all of which have been studied previously. However, unlike other quantum dots, it is difficult to build an outer shell like ZnS, and it has the disadvantage of very poor stability. In order to overcome this, it is necessary to increase the stability of perovskite through other methods: ⅰ) Strong binding energy: To maintain the structure of perovskite, it must be synthesized using an element with a stronger binding energy than the element previously used. In the case of synthesis using these elements, resistance to other external environments can be generated, thereby increasing the surface oxidation and structural stability. ⅱ) Surface stability by organic matter: This replaces the existing organic matter with another one on the surface of the quantum dots that preferentially contacts the external environment and improves the stability from the surface to the inside of the structure. In Chapter 1, the mixed cation CsxRb1-xPbX3 PeQDs, which have a cubic structure, were synthesized by water treatment. It has shown high quantum yields of about 93% and 86% for the luminescence of green and blue wavelengths, respectively. Especially, the stability is improved under harsh conditions such as high temperatures, ultraviolet (UV) irradiation, and water, and we checked it in the solution, powder, and film states. We explained the reason for these improved properties through exciton binding energy calculation and an increase in the defect formation resistance with Rb incorporation. Also, we fabricated PeQDs film for an LCD color filter using cyclic olefin copolymer (COC) as an optical polymer with high light transmittance and water resistance. The films produced have a wide color gamut covering up to 104.15% of the BT.2020 color space and high stability. We also confirmed that the white light color temperature of 5299K, coordinates of (0.33, 0.32), and luminance of 68.86 Cd/m2 at 20mA. In Chapter 2, thiol (-SH) capped CsPbI3 PeQDs were synthesized through ligand exchange. The surfactants that commonly used such as oleic acid (OA) and oleylamine (OLA) are unstable on the surface of PeQDs, and they readily degraded the optical properties owing to weak binding and steric hindrance. In particular, among the PeQDs, CsPbI3 QDs with red luminescence were very structurally weak, and it was difficult to maintain excellent optical properties. To solve these problems, we applied thiol, an X-type, as a capping ligand, not an L-type ligand such as OA and OLA, which was used previously. Thiol with a strong bonding force was often used to stabilize the surface of quantum dots. The synthesized -SH capped CsPbI3 PeQDs show a distinct effect on photostability under ultraviolet (365nm) irradiation by a ligand exchange method from OA and OLA to -SH. Since the photostability to the backlight was improved, it was used as a color filter for the LCD. Likewise, perovskite films were fabricated by using the PeQDs and COC, and we checked the photostability of -SH capped CsPbI3/COC films and it exhibited a higher stability than the untreated films irradiated by a blue backlight unit (BLU). In Chapter 3, a new metal-ligand complex was synthesized based on the fact that the metals and ligands of the two studies above increased the stability of perovskite quantum dots further. In order to apply quantum dots to an EL (electroluminescence) device, a new ligand is needed because a small amount of the ligand must effectively protect the surface. We developed a TOPO-Zn (trioctylphosphine oxide-zinc) complex and applied it to perovskite quantum dots to effectively improve the stability. We confirmed that the TOPO-Zn complex was formed through 31P NMR, and by measuring the surface state of PeQD through XPS analysis we proved why the stability was improved by effectively removing oxygen in the surface and structure, hence proving the reason for the improved stability. The synthesized PeQD had a high quantum efficiency and stability, and as a result an EL device was produced, and furthermore, a hybrid device of EL and PL was produced by coating the OLED using aerosol deposition, with a fine pattern of about 30um from a large area. It was confirmed that it can be applied to various fields by coating it on the flexible substrate.

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목차

제1장 General Introduction 1
제1절 Quantum dots 2
1. Definition of quantum dots 2
2. Types and Composition of Quantum Dots 4
3. Types of quantum dots by the band structure of shells 5
4. Type of Surfactant 6
제2절 Inorganic perovskite quantum dots 8
1. Definition of perovskite 8
제3절 Application 11
1. Color converting film for liquid crystal displays 11
2. Quantum dot-based light-emitting diodes 13
제2장 Material development for the fabrication of full color films with high stability and wide color gamut 15
제1절 Development of Mixed-Cation CsxRb1–xPbX3 Perovskite Quantum Dots and Their Full-Color Film with High Stability and Wide Color Gamut 16
1. Introduction 17
2. Experiment section 20
3. Results and discussion 24
4. Conclusions 40
제2절 Highly photostable CsPbI3 perovskite quantum dots via thiol ligand exchange and their polymer film application 41
1. Introduction 42
2. Experiment section 44
3. Results and discussion 46
4. Conclusions 56
제3장 Development of stable and highly efficient materials for electroluminescence 57
제1절 Highly Stable All-Inorganic Perovskite Quantum Dots Using a ZnX2-Trioctylphosphine-Oxide: Application for High-Performance Full-Color Light-Emitting Diode 58
1. Introduction 59
2. Experiment section 62
3. Results and discussion 64
4. Conclusions 97
제4장 Conclusions 98
1. Conclusions 99
제5장 References 100

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