새로운 구조 및 공정 설계를 통한 양자점의 전기적 광학적 특성 향상에 관한 연구
초록/요약
This Paper aims to understanding and improvement of the quantum dots (QDs) which is the most highlighted nano material. Some tasks should be carried out for the commercialization and popularization of QDs. i) Mass production : The main synthetic methods in lab scale are not suitable for mass production. ii) Enhancement of property and Finding new property : Nano sized materials show unique properties which are not shown in bulk state. So, it is very interesting that they show property change with change of their size. The critical condition for property improvement should be checked out. The research about a novel property on their size changes in nano scale also should be conducted. iii) Stabilization: QDs is a very tiny particle that they have a large surface area. The large surface area is a key point of unique property for nano-sized materials, but the unstable surface should be stabilized essentially. Namely, surface oxidation and aggregation that reducing the properties should be suppressed for further application. The new structural and process designs are proposed to solve these tasks. In chapter 1, It is mentioned about the enhancement of property of PbS QDS via new structural design. PbS is usually used as a light absorber in solar cell, and the large amount of light absorption can lead the improvement of power conversion efficiency(PCE). Copper cation is introduced by cation exchange reaction into the pristine PbS, and CuS is partially embedded in PbS. CuS can absorb the IR range through SPR effect, amount of the total absorbed light is dramatically increased. Besides, the exciton is separated into electron and hole freely in CuS, the energy consumption for separation of exciton is saved. The final PEC of 8.07% is obtained under 1 sun condition (100mWcm-2 AM 1.5G). (Voc 0.6V, Jsc 20.7mAcm-2, FF 65%) In chapter 2, It is mentioned about the stability improvement of PbS QDs via new structural design. The PbS which has a large surface area can be oxidized easily. In solar cell fabrication, new protection method is needed, because outer shell which can protect the surface is limited due to the electron and hole extraction. The galvanic protection method is used for surface protection. The surface can be protected by introducing magnesium which is more easily oxidized than the lead. The immoderate oxidation occurs when excess magnesium is used. The magnesium oxide acts as seed of oxidation. The improved stability is confirmed by stability test using solar cell. They have worked stably for two days without property change. The final PCE of 4.4% is obtained under 1 sun condition (100mWcm-2 AM 1.5G). (Voc 0.6V, Jsc 11.8mAcm-2, FF 62.8%) In chapter 3, The galvanic protection method is applied to other QDs. It was applied to InP/GaP/ZnS which already have outer shell. They also present improved stability. It is confirmed by fabrication of white light device, and they present good results. They show a resistance to thermal stress during the fabrication procedure, they show a compatibility with relative materials. Finally, The PCE of 129.57lmW-1, CRI of 84.4 CCT of 3799k were obtained. In chapter 4, It is mentioned about the new synthetic procedure for mass production of InP/GaP/ZnS. The heating-up method was used instead of the established hot-injection method. The core/shell/shell structure has been synthesized at once. InP core and GaP inner shell can be synthesized sequentially due to the reactivity difference of phosphorus between indium and gallium. In last step, reaction can be controlled by addition of dodecanethiol (DDT). The growth of core is inhibited by addition of DDT at low temperature, and ZnS outer shell is formed. The thickness of ZnS shell is tuned by the kinds of used DDT. The n-DDT which have low reactivity form a thin outer shell, and the t-DDT which have high reactivity form a thick outer shell. The entire visible range was realized by core size control using this method. T the optical property is kept, although the reaction is finished within 30 min. In chapter 5, It is mentioned about the stability improvement through formation of QD-polymer composite via in-situ solvent polymerization. The double bond on ODE used as a solvent is activated with alkyl aluminum catalyst after the QD synthesis. To compared with other polymerizations, the QDs are uniformly embedded in the composite due to the direct polymerization of uniformly dispersed QDs. The polymer can protect the QDs stably by forming a protection layer. The white light device was fabricated to confirm the stability of QD-polymer composite. They present improved stability compared with bare QDs which present a low stability during the fabrication procedure. Especially, target CCT and high CRI can be achieved by mixing up with green and red composite, and they show a great possibility for high functional lighting. (#1 PCE 58.7lmW-1, CRI 92, CCT 3401k #2 PCE 61.1lmW-1, CRI 90, CCT 6337k)
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Table of Contents
Acknowledgement i
Abstract ii
Table of Contents iv
List of Figures viii
List of Tables xi
PART 1. General Introduction 1
1. Nano material 2
2. Quantum dots 6
2.1. QDs? 11
2.1.1. Introduction of QDs 11
2.1.2. Synthetic method for QDs 7
2.2. QD classify 8
2.2.1. Classify by the core property 8
2.2.2. Classify by structure 8
2.2.3. Classify by the band structure 9
2.3. Application 11
2.3.1. Solar cell 11
2.3.2. Display 13
2.3.3. Lighting 15
3. Problems 17
3.1. Producibility 17
3.2. Stability 18
3.2.1. Toxicity 18
3.2.2. Stability 18
PART 2. New structural design for QDs 20
Chapter 1. Highly efficient solid-state mesoscopic PbS embedding CuS quantum dot-sensitized solar cells 21
1. Introduction 22
2. Experiment section. 25
2.1. Materials 25
2.2. Preparation of PbS[CuS] QDs 25
2.3. Cell fabrication 26
2.4. Measurement 26
2.4.1. Material characterization 26
2.4.2. Device characterization 26
3. Results and discussion 28
4. Conclusions 41
Chapter 2. Exceptional stability of Mg-implemented PbS quantum dot solar cells realized by galvanic corrosion protection 42
1. Introduction 43
2. Experiment section 46
2.1. Materials 46
2.2. Preparation of 0.5% Mg-PbS QDs 46
2.3. Cell fabrication 46
2.4. Measurement 47
2.4.1. Material characterization 47
2.4.2. Device characterization 47
3. Results and discussion 48
4. Conclusions 61
Chapter 3. Surface stabilized InP/GaP/ZnS QDs with Mg ions for WLED application 62
1. Introduction 63
2. Experiment section 65
2.1. Materials 65
2.2. Preparation of InP/GaP/Mg-ZnS QDs 65
2.3. LED device fabrication 66
2.4. Measurement 66
2.4.1. Material characterization 66
3. Results and discussion 67
4. Conclusions 75
PART 3. New process design 76
Chapter 4. Highly luminescent InP/GaP/ZnS QDs emitting in the entire color range via a heating up process 77
1. Introduction 78
2. Experiment section 80
2.1. Materials 80
2.2. Preparation of blue QDs 80
2.3. Preparation of green QDs 80
2.4. Preparation of red QDs 81
2.5. Measurement 82
2.5.1. Materials characterization 82
2.5.2. Quantum Yield (QY) measurement 82
3. Results and discussion 84
4. Conclusions 97
Chapter 5. Highly stable Cd free quantum dot/polymer composites and their WLED application 98
1. Introduction 99
2. Experiment section 101
2.1. Materials 101
2.2. Preparation of QD and QD-composite. 101
2.2.1. Synthesis of QD 101
2.2.2. Synthesis of QD-polymer composite 102
2.3. LED device fabrication 104
2.3.1. All QD device 104
2.3.2. Phosphor & QD device 104
2.4. Measurement 104
2.4.1. Material characterization 104
3. Results and discussion 106
4. Conclusions 118
PART 4. Conclusions 119
1. Conclusions 120
PART 5. References 121
Abstract in Korean 136
Publications & Patent 139
