臺灣博碩士論文加值系統

本篇論文有兩個研究主題。其一為複合激發體觸發三重態-三重態湮滅藍色有機發光二極體之效率提升研究。其二為利用咔唑基團與咪唑基團合成之衍生物作為不同熱活化延遲螢光發光體之通用主體材料之研究。
我們利用具有推電子及拉電子特性的有機材料形成複合激發體，再藉由能量傳遞將能量傳給藍色螢光材料進行三重態-三重態湮滅上轉換得到藍光，我們稱為複合激發體觸發三重態-三重態湮滅過程。藉由嵌入一層三重態傳遞和單重態阻隔層以及加入螢光客體材料，可以達到最高外部量子效率5.1%，其中包含藍色部分3.8%。最後以電激發元件觀察激子的暫態行為，暫態放光中並沒有瞬時螢光的產生，而只有經由能量轉移形成的延遲螢光，表示此架構的藍光都是來自於複合激發體觸發三重態-三重態湮滅的過程。
利用咔唑基團與咪唑基團合成之衍生物作為藍色、綠色及紅色熱活化延遲螢光發光體之通用主體材料，期望簡化製程步驟及降低生產成本。經過元件結構的調整與優化，藍色、綠色與紅色熱活化延遲螢光之高效率有機發光二極體的最大電流效率、功率效率及外部量子效率分別為11.3 cd/A、91.8 cd/A及31.4 cd/A、11.9 lm/W、91.9 lm/W及28.2 lm/W與9.0%、26.2%及11.5%。也成功展現此主體材料作為熱活化延遲螢光發光體之通用主體材料的可行性。

There are two topics in this thesis. The first one is efficiency enhancement of exciplex sensitized triplet-triplet annihilation (ESTTA) blue organic light emitting diodes (OLEDs). The second one is red, green, blue OLEDs with 9,9''-(2-(1-Phenyl-1H-benzo[d]imidazol-2-yl)-1,3-phenylene)bis(9H-carbazole) (o-DiCbzBz) as the universal host material for thermally activated delayed fluorescence (TADF) emitters.
The exciplex was formed at interface of electron donor and acceptor organic materials, then triplet energy transfer (TET) to TTA blue emitter to generate upconversion blue emission, which was called exciplex sensitized triplet-triplet annihilation (ESTTA) process. With insertion of triplet assisting and singlet blocking (TASB) layer and incorporation of fluorescent dopant, the blue ESTTA-OLED exhibited maximum external quantum efficiency (EQE) of 5.1% including blue emission EQE of 3.8%. In addition, transient electroluminescence (TrEL) was used to examine the origin of blue emission. In turn-off luminance response, only slow decay was observed implying blue emission all came from exciplex energy transfer to emitter to facilitate TTA upconversion emission, called ESTTA process.
o-DiCbzBz was used as host material, doped with metal-free red, green, and blue TADF dopants to achieve high efficiency OLEDs in order to simplify manufacturing process and reduce production cost. After the optimization of the device structure, maximum current efficiency of 11.3 cd/A, 91.8 cd/A, and 31.4 cd/A, maximum power efficiency of 11.9 lm/W, 91.9 lm/W, and 28.2 lm/W, and maximum EQE of 9.0%, 26.2%, and 11.5% were obtained for blue, green, and red TADF-OLEDs, respectively, showing the feasibility of o-DiCbzBz as the universal host for RGB high efficiency TADF-OLEDs.

摘要 I
Abstract III
List of Figures VII
List of Tables XVII
Chapter 1 Introduction 1
1.1 ESTTA-OLED 2
1.1.1 Sensitized triplet-triplet annihilation in liquid phase with optical pumping 2
1.1.2 Sensitized triplet-triplet annihilation in solid phase with optical pumping 5
1.1.3 OLED with exciplex host 8
1.1.4 ESTTA-OLED 11
1.1.5 Excitons blocking and management 14
1.1.6 Motivation 21
1.2 TADF-OLEDs 21
1.2.1 Introduction to TADF-OLEDs 21
1.2.2 Universal host materials for high efficiency RGB PhOLEDs 28
1.2.3 Motivation 32
Chapter 2 Experiments 33
2.1 Introduction 33
2.2 OLED fabrication process 33
2.3 Measurement systems 34
2.3.1 Luminance-current density-voltage (L-J-V) system 34
2.3.2 Transient electroluminescence (TrEL) measurement 35
Chapter 3 Efficiency enhancement of exciplex sensitized triplet-triplet annihilation blue organic light emitting diodes 37
3.1 Introduction 37
3.2 ESTTA OLEDs with optimized EQE 40
3.3 Adjusting TASB layer thickness 46
3.3.1 Steady state L-J-V characteristics 48
3.3.2 TrEL analysis 51
3.4 Adjusting EML and ETL thickness 56
3.4.1 Steady state L-J-V characteristics 57
3.4.2 TrEL analysis 60
3.5 Incorporation of a fluorescent dopant 64
3.5.1 Steady state L-J-V characteristics 65
3.5.2 TrEL analysis 68
3.6 Effects of TASB layer 71
3.6.1 Steady state L-J-V characteristics 72
3.6.2 TrEL analysis 75
3.7 Comparison with pure exciplex OLED 79
3.7.1 Steady state L-J-V characteristics 80
3.7.2 TrEL analysis 82
3.8 Comparison with blue TTA OLED 84
3.8.1 Steady state L-J-V characteristics 85
3.8.2 TrEL analysis 88
3.8.3 Operation lifetime comparison of TTA and ESTTA OLEDs 90
Chapter 4 o-DiCbzBz as the host material for blue, green, and red TADF-OLEDs 96
4.1 Introduction 96
4.2 Blue, green, and red TADF-OLEDs with their optimized structures 97
4.3 Optimization of blue TADF OLEDs 103
4.3.1 Adjusting doping concentration 104
4.3.2 Tuning ETL thickness 109
4.3.3 Tuning EML thickness 112
4.4 Optimization of green TADF OLEDs 116
4.4.1 Adjusting doping concentration 116
4.4.2 Tuning ETL thickness 121
4.4.3 Tuning EML thickness 124
4.5 Optimization of red TADF OLEDs 128
4.5.1 Adjusting doping concentration 128
4.5.2 Tuning ETL thickness 133
4.5.3 Tuning EML thickness 136
4.6 Transient electroluminescence (TrEL) measurement of TADF OLEDs 139
4.6.1 Introduction 139
4.6.2 Pulsewidth and repetition rate of TrEL measurement 139
4.6.3 TrEL measurements with different current density 142
4.6.4 TrEL measurements with reverse bias effect during turned-off period 145
4.6.5 Alternating current (AC) driving TADF-OLEDs 150
Chapter 5 Summary 153
References 155

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