Title Page

Contents

List of abbreviation 16

Abstract 22

Chapter 1. Introduction 24

1.1. Basic structure of organic light-emitting diodes 24

1.2. Emitter types and emission mechanisms in OLEDs 27

1.3. Current and future OLED applications 30

1.4. Current issues with red emitters in OLEDs 33

1.5. Approach methods for highly efficient red dopant 36

1.5.1. Various efficiency factors of OLEDs 36

1.5.2. Relationship between efficiency and radiative decay rate 41

Chapter 2. Design Strategy for Highly Efficient and Stable Pt(II) Red Dopants by Singlet-Triplet Energy Gap Control 46

2.1. Introduction 46

2.1.1. History and issues of Pt(II) red phosphorescent dopants 46

2.1.2. Design strategy for highly efficient Pt(II) red dopants 51

2.2. Experimental 54

2.2.1. General information 54

2.2.2. Synthesis 56

2.2.3. Device fabrication 67

2.2.4. Computational methods 69

2.3. Results & Discussion 70

2.3.1. Study for efficiency improvement 70

2.3.2. Study for device lifetime improvement 87

2.3.3. Molecular optimization for highly efficient and stable Pt(II) red-dopants 100

2.4. Conclusions 115

Chapter 3. Development of Novel Chromophore for Highly Efficient Ir(III) Red Dopants Using Transition Dipole Moment 117

3.1. Introduction 117

3.1.1. Issues of Ir(III) red phosphorescent dopant 117

3.1.2. Design strategy for highly efficient Ir(III) red dopants 120

3.2. Experimental 125

3.2.1. General information 125

3.2.2. Synthesis 126

3.2.3. Device fabrication 137

3.3. Results and Discussion 138

3.4. Conclusions 163

References 164

논문요약 173

Chapter 2 10

Table 2-1. Summary of the molecular caculations for RD01 to RD05. 72

Table 2-2. Summary of orbital composition distribution using the NTO plot. 75

Table 2-3. Summary of material property data for RD01, RD02, and RD03. 80

Table 2-4. Summary of OLED device performance for RD01 and RD02. 83

Table 2-5. Summary of molecular calculations for RD06, RD07 and comparison with RD01. 89

Table 2-6. Summary of material property data for RD06, RD07, and comparison with RD01. 95

Table 2-7. Summary of OLED device performance for RD06, RD07, and comparison with RD01. 99

Table 2-8. Summary of molecular calculations for RD08, RD09, and comparison with RD01. 103

Table 2-9. Summary of material property data for RD09 and comparison with RD01. 106

Table 2-10. Summary of OLED device performance for RD09, RD09R', and comparison with RD01. 109

Chapter 3 11

Table 3-1. C-C bond lengths of the specific benzene ring in RD-IQ, RD-BIQ-A, and RD-BIQ-B. 143

Table 3-2. Summary of molecular calculations for RD-IQ, RD-BIQ-A, and RD-BIQ-B. 145

Table 3-3. Summary of material property data for RD-IQ, RD-BIQ-A, and and RD-BIQ-B. 151

Table 3-4. Summary of OLED device performance for RD-IQ, RD-BIQ-A, and RD-BIQ-B. 161

Chapter 1 12

Figure 1-1. Basic OLED structure and component layer functions. 25

Figure 1-2. Mechanisms of fluorescence and phosphorescence in the Jablonski diagram. 27

Figure 1-3. OLED technology roadmap to the future. 30

Figure 1-4. (a) Comparison of BT2020(or Rec2020) and Adobe RGB in CIE index. (b) S₁(or T₁)-S₀ vibrational coupling by small energy bandgap. 34

Chapter 2 12

Figure 2-1. Development history of red phosphorescent dopants. 48

Figure 2-2. S₁ energy control for reducing △EST.[이미지참조] 53

Figure 2-3. Molecular design concept for reducing △EST.[이미지참조] 71

Figure 2-4. Chemical structures and calculated distributions of HOMOs and LUMOs at lowest triplet excited state. 74

Figure 2-5. (a) PL emission spectra, and (b) transient PL decay curve for RD01, RD02, and RD03. 79

Figure 2-6. (a) Energy level diagram and (b) chemical structure of materials used in OLED devices. 83

Figure 2-7. (a) Current density-Voltage-Luminance curves, (b) external quantum efficiency-luminance, and (c) EL spectra of RD01, RD02 devices. 85

Figure 2-8. Device lifetime for RD01 and RD02 at 25 mA/cm². 86

Figure 2-9. (a) Conceptual molecular design for reducing intermolecular interactions and (b) resulting new dopant structure. 88

Figure 2-10. (a) The three-dimensional structure and (b) accessible ratio for RD01, RD06, and RD07. 91

Figure 2-11. Comparison of PL emission spectra for RD01, RD06, and RD07. 94

Figure 2-12. (a) EL spectrum and (b) external quantum efficiency-luminance of RD01, RD06, and RD07 devices. 97

Figure 2-13. Device lifetime comparison for RD01, RD06, and RD07 at 3,000 cd/m². 98

Figure 2-14. The design concept for high efficiency and long device lifetime. 101

Figure 2-15. Comparison of the PL emission spectra for RD01 and RD09. 105

Figure 2-16. Current density-Voltage characteristics of (a) electron-only device (EOD) and (b) hole-only device (HOD) with 2 wt% RD01 or RD09... 110

Figure 2-17. The energy level diagram of RD09R' OLED device and chemical structure of R'. 111

Figure 2-18. (a) Current density-Voltage curves, (b) external quantum efficiency-luminance, and (c) EL spectra of RD01, RD09, and RD09R' devices. 113

Figure 2-19. Device lifetime comparison for RD01, RD09, and RD09R' at 3,000 cd/m². 114

Figure 2-20. Novel RD09 dopant with outstanding performance and UHD color gamut. 116

Chapter 3 14

Figure 3-1. Classification of first- and second-generation Ir(III) red phosphorescent dopants according to main ligand structures. 119

Figure 3-2. The attempted design for reducing the △EST factor in an Ir(III) red dopant with a piq ligand, and the expected wavelength of the peak emission.[이미지참조] 124

Figure 3-3. Novel Ir(III) red dopant design concept to enhance the TDM factor without red-shift in the emission wavelength. 141

Figure 3-4. Ground state density functional theory calculations for RD-IQ, RD-BIQ-A, and RD-BIQ-B. 142

Figure 3-5. Molecular orbital calculation results of RD-IQ, RD-BIQ-A, and RD-BIQ-B. 144

Figure 3-6. (a) UV-vis absorption and PL emission spectra, and (b) transient PL decay curve for RD-IQ, RD-BIQ-A, and RD-BIQ-B. 150

Figure 3-7. TGA data for RD-IQ, RD-BIQ-A, and RD-BIQ-B under ambient pressure (1 atm). 153

Figure 3-8. TGA data for (a) RD-IQ, (b) RD-BIQ-A, and (c) RD-BIQ-B under reduced pressure (1 Pa). 155

Figure 3-9. (a) Current density-Voltage-Luminance curves, (b) external quantum efficiency-luminance, and (c) EL spectra of RD-IQ, RD-BIQ-A,... 160

Figure 3-10. Horizontal ratio analysis of RD-IQ, RD-BIA-A, and RD-BIQ-B based on angle-dependent PL measurements. 162

Chapter 2 9

Scheme 2-1. Synthetic procedure for RD02. 56

Scheme 2-2. Synthetic procedure for RD03. 59

Scheme 2-3. Synthetic procedure for RD06. 61

Scheme 2-4. Synthetic procedure for RD07. 63

Scheme 2-5. Synthetic procedure for RD09. 64

Scheme 2-6. Schematic of the synthesis process for RD01 to RD04. 76

Chapter 3 9

Scheme 3-1. Synthetic procedure for RD-IQ. 126

Scheme 3-2. Synthetic procedure for RD-BIQ-A. 128

Scheme 3-3. Synthetic procedure for RD-BIQ-B. 132

Scheme 3-4. Schematic of the synthesis process for RD-BIQ-A and RD- BIQ-B. 146