Embedded Nanostructures for High Efficiency Organic Light Emitting Devices
나노 구조 내장 고효율 유기 발광 소자

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dc.description학위논문 (박사)-- 서울대학교 대학원 : 재료공학부, 2014. 2. 윤재륜.-
dc.description.abstractOrganic light emitting diodes (OLEDs) have been successfully applied to various mobile electronics because the display, which utilizes a spontaneous emission of light from organic molecules by nature, is a very energy efficient way to produce vibrant images. However, only around 20-30% of the light generated by a typical bottom emission OLED is extracted into the air because the light intensity is decreased by a factor of 1/2n2 as the light passes through each layers, where n is the refractive index (RI).
The light extraction efficiency, which is one of the most important factors, can be enhanced by applying photonic implements to each layer. In this thesis, a nano-hole array (NHA) embedded OLEDs were proposed for light extraction. The NHA structure is proposed as a strategy for escaping the loss mode wasted by the substrate, waveguided and surface plasmon polaritons. Various methods have been proposed to convert the loss modes into the radiation mode, e.g., polymer/Si3N4 nano hole array embedded OLEDs (chapter 3), vacuum/Si3N4 nano hole array embedded OLEDs (chapter 4 and chapter 7), corrugated OLEDs (chapter 5) and their combinations (chapter 6).
The enhanced performance of the nanostructure embedded OLEDs is evaluated by using in terms of photoluminescence (PL) and electroluminescence (EL), and the finite difference time domain (FDTD) simulation was carried out to analyze the optical performance of the NHA structure for extraction of the emission. We explored the effect of the NHA structure on the extraction improvement converted from waveguide mode by measuring EL intensities of the devices with hemisphere lens. The reduction of power dissipation to waveguide and surface plasmon modes by applying the NHA structure leads to strongly enhance the out-coupling efficiency of OLEDs.
Especially the robust reverse transfer process was newly developed for confining the nano hole array in the vacuum state. The periodic nano hole array is inserted in the vacuum state to maximize the refractive index contrast of the PhC slab for a given background high-refractive index material. In addition, the transfer process employed in VNHA fabrication yielded extremely low surface roughness, and thus outstanding electrical characteristics. We obtained an extremely high efficiency OLEDs with over 50% of external quantum efficiency (EQE) and low roll-off by inserting vacuum nano hole array (VNHA) into phosphorescent OLEDs (PhOLEDs), and it is the highest EQE for bottom-emitting OLEDs.
dc.description.tableofcontentsAbstract i
List of Figures vii
List of Tables xiv

Chapter 1. Introduction 15
1.1 OLED fundamentals 15
1.2 Electroluminescence quantum efficiency 16
1.3 Optical loss modes 22
1.4 Bibliography 25

Chapter 2. Motivation 27

Part І
Nano Hole Array Embedded Organic Light Emitting Diodes
Chapter 3. Polymer Nanostructure Embedded Organic Light Emitting Diodes 30
3.1 Introduction 30
3.2 Experimental 32
3.2.1 Imprinted polymer nano hole array fabrication 32
3.2.2 Polymer/Si3N4 PhCs slab characterization 32
3.3 Finite Difference Time Domain Simulation 35
3.4 Electroluminescence Performance 37
3.5 Conclusions 40
3.6 Bibliography 40

Chapter 4. Vacuum Nano Hole Array Embedded Organic Light Emitting Diodes: Fluorescent Molecules as an Emitter 42
4.1 Introduction 42
4.2 Experimental 44
4.2.1 VNHA substrate fabrication 44
4.2.2 VNHA OLEDs characterization 48
4.3. FDTD Analysis 48
4.3.1 Effect of the refractive index contrast 48
4.3.2 Emission energy for the three primary colors 50
4.4 Angular Dependence of Photoluminescence 55
4.5 Electroluminescence of VNHA OLEDs 57
4.5.1 Intensified CCD measurement 57
4.5.2 EL intensity of half-sphere lens attaching OLEDs 61
4.5.3 Diffraction pattern induced from substrate modes 61
4.5.4 J-V-L curves of VNHA OLEDs 62
4.6 Conclusions 66
4.7 Bibliography 67

Part II
Corrugated Organic Light Emitting Diodes
Chapter 5. Corrugated Organic Light Emitting Diodes 70
5.1 Introduction 70
5.2 Experimental 73
5.2.1 Corrugated OLEDs fabrication 73
5.2.2 Characterization of corrugated OLEDs 75
5.3 Electroluminescence Performance 75
5.3.1 J-V-L characteristics of corrugated OLEDs 75
5.3.2 EL enhancement evaluated by intensified CCD 76
5.3.3 Radiation profile of corrugated OLEDs 77
5.3.4 Device stability and life-time 81
5.4 FDTD Analysis 84
5.4.1 FDTD structure for considering Bragg gratings 84
5.4.2 Comparison between theoretical and empirical results 85
5.5 Conclusions 87
5.6 Bibliography 87

Chapter 6. Corrugated OLEDs Embedding Vacuum Nano Hole Array
6.1 Introduction 89
6.2 Multiple Nano Patterned Substrate 90
6.2.1 MNHA substrate fabrication 90
6.2.2 MNHA substrate characterization 92
6.3 FDTD Analysis 96
6.3.1 Corrugated OLEDs embedding VNHA
: Localized surface plasmon at the distorted metal surface 96
6.3.2 Poynting energy depending on the overlay shift 101
6.4 Angular Photoluminescence 105
6.5 Electroluminescence 108
6.5.1 Intensified CCD measurement 108
6.5.2 J-V-L characteristics 113
6.6 Conclusions 116
6.7 Bibliography 116

Part III
Ultrahigh-Efficiency OLEDs
Chapter 7. Vacuum Nano Hole Array Embedded OLEDs with Ultimate Efficiency: Phosphorescent Molecules as an Emitter 119
7.1 Introduction 119
7.2 Experimental 121
7.2.1 VNHA substrate fabrication 121
7.2.2 VNHA-PhOLEDs fabrication 124
7.2.3 VNHA-PhOLEDs characterization 127
7.3 Mode Analysis by Optical Modeling 127
7.4 Photoluminescence Performance 130
7.4.1 Polarized angular photoluminescence 130
7.4.2 Comparison of PL with dipole orientations 131
7.5 Electroluminescence Performance 133
7.5.1 External quantum efficiency and power efficiency 133
7.5.2 Hemi-sphere attaching VNHA-PhOLEDs 134
7.6 Conclusions 139
7.7 Bibliography 139

Appendix A. VNHA Substrate Characterization Details 142
Appendix B. FDTD Simulation Details 147
Appendix C. Angular PL Measurement Details 154
Appendix D. EL Measurement Set-up 157

Korean Abstract 158
dc.format.extent10274338 bytes-
dc.publisher서울대학교 대학원-
dc.subjectLight Extraction-
dc.subjectPhotonic Crystals-
dc.subjectDiffraction Strength-
dc.subjectSurface Plasmon-
dc.titleEmbedded Nanostructures for High Efficiency Organic Light Emitting Devices-
dc.title.alternative나노 구조 내장 고효율 유기 발광 소자-
dc.citation.pagesxiv, 159-
dc.contributor.affiliation공과대학 재료공학부-
Appears in Collections:
College of Engineering/Engineering Practice School (공과대학/대학원)Dept. of Materials Science and Engineering (재료공학부)Theses (Ph.D. / Sc.D._재료공학부)
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