Title Page

Contents

Abstract 12

Chapter 1. INTRODUCTION 14

1.1. Colloidal Quantum Dots 14

1.2. Quantum Dot-Based Light-Emitting Diodes 20

1.3. Environmentally benign InP Quantum Dots 22

Chapter 2. EXPERIMENTAL 24

2.1. Materials 24

2.2. Synthesis of green-emitting InP/ZnSe/ZnS core/shell/shell Quantum dots 25

2.2.1. Precursors 25

2.2.2. InP core synthesis 26

2.2.3. Growth of ZnSe inner shell on InP core 27

2.2.4. Growth of ZnS outer shell on InP/ZnSe core/shell QDs. 27

2.3. Engineering the surface ligands of InP/ZnSe/ZnS QDs 28

2.4. Fabricating green-emitting InP/ZnSe/ZnS QD-LEDs 29

2.4.1. Synthesis of ZnO (ZnxM₁-x) NPs[이미지참조] 29

2.4.2. Device fabrication 30

2.5. Characterization 30

2.5.1. UV-vis and Photoluminescence spectrophotometer 30

2.5.2. Transmission Electron Microscopy 31

2.5.3. Ultraviolet Photoelectron Spectroscopy 31

2.5.4. Stability test 31

2.5.5. Nuclear Magnetic Resonance Analysis 32

2.5.6. Thermogravimetric Analysis and differential scanning calorimetry 32

2.5.7. Time-resolved photoluminescence and time-correlated single photon counting 32

2.5.8. QLED-characterization 33

Chapter 3. RESULTS AND DISCUSSION 34

3.1. Structure engineering of InP/ZnSe/ZnS QDs 34

3.1.1. Growth of ZnSe inner shell on InP core 35

3.1.2. Growth of ZnS outer shell on InP/ZnSe core/shell QDs 38

3.2. Surface ligands engineering of InP/ZnSe/ZnS QDs 40

3.3. Impact of engineered QDs on light-emitting diodes performance 45

3.3.1. Impact of ZnSe/ZnS shell thickness on device performance 45

3.3.2. Impact of ligand engineered QDs on device performance 49

Chapter 4. CONCLUSION 59

References 61

논문요약 67

Table. 1. Device characteristics of InP-based QLEDs 58

Figure 1.1. Schematic structure of core/shell heterostructured QD. 14

Figure 1.2. Schematic diagram of energy structure of bulk material and various size of QDs. 15

Figure 1.3. Schematic diagram of Type-I, Type-II, Quasi-type II band structure with electron(red line) and hole(blue line) wavefunction. 16

Figure 1.4. (a) Schematic illustration of device structure [4]. (b) Charge transfer in conventional and inverted InP-based QLEDs [5]. (c) Energy levels... 21

Figure 3.1. Absorption and PL spectra of InP (r ＝ 1.2 nm)/ZnSe (l nm)/ZnS (h ＝ 0.6 nm) QDs upon ZnSe shell thickness. (a) l ＝ 2.0, 2.8, 3.2 nm, (b) l ＝ 3.2,... 36

Figure 3.2. (a)~(f) TEM image of InP(r ＝ 1.2 nm)/ZnSe(l nm)/ZnS(h ＝ 0.6 nm) QDs. ZnSe thickness (l), l ＝ 2.0 nm (left of top line), 2.8 nm (middle of top... 37

Figure 3.3. PL decay dynamics of InP/ZnSe/ZnS QDs on ZnSe shell thickness. ZnSe shell thickness (l), l ＝ 2.0 nm (gray), 2.8 nm (blue), 3.2 nm (black). 37

Figure 3.4. Absorption and emission spectra of InP (r ＝ 1.2 nm)/ZnSe (l ＝ 2.8 nm)/ZnS (h, nm) QDs. h ＝ 0.6 nm (black), 0.8 nm (red), 1.0 nm (blue). 39

Figure 3.5. PL decay dynamics of InP (r ＝ 1.2 nm)/ZnSe (l ＝ 2.8 nm)/ZnS (h, nm) QDs upon ZnS shell thickness. h ＝ 0.6 nm (black), 0.8 nm (red), 1.0 nm (blue). 39

Figure 3.6. The tendency of PL QY over 2 weeks based on the thickness of ZnS shell observed through stability test. InP(r ＝ 1.2 nm)/ZnSe (l ＝ 2.8 nm)/ZnS... 40

Figure 3.7. Absorption and PL spectra of InP (r ＝ 1.2 nm)/ZnSe (l ＝ 2.8 nm)/ZnS (h ＝ 0.6 nm) QDs with different ligand length on the surface. 42

Figure 3.8. TGA results and PL QY of InP (r ＝ 1.2 nm)/ZnSe (l ＝ 2.8 nm)/ZnS (h ＝ 0.6 nm) QDs with different ligand length on the surface. 42

Figure 3.9. Absorption and emission spectra of InP (r ＝ 1.2 nm)/ZnSe (l ＝ 2.0, 2.8 nm)/ZnS (0.6 nm) with the X, L, Z-type of ligands on surface. 44

Figure 3.10. NMR results of InP (r ＝ 1.2 nm)/ZnSe (l ＝ 2.0 nm)/ZnS (0.6 nm) QDs with (a) OA surface ligands and (b)OAm surface ligands. 44

Figure 3.11. (a) Current density (J)−voltage (V)–Luminance (L) characteristics of QD-LEDs (b) EQE versus luminance characteristics with... 46

Figure 3.12. (a) Current density (J)−voltage (V)–Luminance (L) characteristics of QD-LEDs (b) EQE versus luminance characteristics of with... 48

Figure 3.13. Current density (J)−voltage (V)–Luminance (L) characteristics of QD-LEDs. Dimension with InP (r ＝ 1.2 nm)/ZnSe (l ＝ 2.8 nm)/ZnS (h ＝ 0.6)... 50

Figure 3.14. (a) Current density (J)−voltage (V)–Luminance (L) characteristics of QD-LEDs (b) EQE versus luminance characteristics of... 50

Figure 3.15. (a) Current density (J)−voltage (V)–Luminance (L) characteristics of QD-LEDs (b) EQE versus luminance characteristics of... 51

Figure 3.16. (a) Current density (J) − voltage (V) – Luminance (L) characteristics of QD-LEDs (b) EQE versus luminance characteristics of... 52

Figure 3.17. (a) Current density (J) − voltage (V) – Luminance (L) characteristics of QD-LEDs (b) EQE versus luminance characteristics of InP... 53

Figure 3.18. Lifetime measurement of various ZnS shell thickness. ZnS shell thickness (h), h ＝ 0.6 (red), 0.8 (yellow), 1.0 nm (blue) 54

Figure 3.19. (a) Current density (J) − voltage (V) – Luminance (L) characteristics of QD-LEDs (b) EQE versus luminance characteristics of InP... 55

Figure 3.20. (a) UPS measurement on InP QDs with/without EHA, OAm and TOP on QDs' surface (b) Up-shifted QDs energy level due to TOP on surface. 56

Figure 3.21. TCSPC measurement of samples on film with before (w/o TOP) and after (w/ TOP) ligand engineering. 57

Figure 3.22. Reported device characteristics of InP-based QLEDs. 58