臺灣博碩士論文加值系統

本篇論文研究方向有二：其一為利用三重態三重態消滅上轉換機制來製作低驅動電壓藍色有機發光二極體，其二為加入輔助主體材料以延長之三重態三重態消滅藍色螢光元件之壽命。
我們利用搭配具有推電子以及拉電子能力的有機材料來形成激發複合體，再藉由能量轉移方式到藍色螢光材料進行三重態三重態消滅上轉換來放出藍光。觀察穩態亮度-電壓特性，利用三重態三重態消滅上轉換機制產生的藍光與一般傳統以直接復合方式相較起來在驅動電壓上降低了0.4伏特。另外我們以電激發光驅動元件觀測低電壓下激子暫態行為，發現當電訊號關掉以後，激子暫態放光中沒有瞬時螢光而全部是經由能量轉移形成的延遲螢光，表示此放光都是來自於三重態的貢獻，證明其機制為三重態三重態消滅上轉換藍光。
我們以加入輔助主體材料來達成89.3%延長壽命之藍色三重態-三重態消滅有機發光體。我們利用量測激子擴散長度、單載子電洞元件、單載子電子元件、探測發光區以及將元件以定電流方式持續操作一段時間後去觀察暫態電激放光，及穩態光激發光頻譜強度的變化，來了解在元件中加入輔助主體材料後扮演的角色。

There are two topics in the thesis. The first one is a blue organic light-emitting diode (OLED) with low driving voltage based on triplet triplet annihilation upconversion (TTAUC) mechanism. And the second is the operation lifetime elongation of triplet triplet annihilation (TTA) blue organic light-emitting diode by introducing assistant host material into the emitting layer (EML).
We use donor and acceptor organic materials to generate exciplex which transfers triplets to the blue TTA material to realize light upconversion, called TTAUC. 0.4 V reduction in turn-on voltage was observed in blue TTAUC-OLED, compared to the conventional TTA-OLED with direct recombination in the EML. Besides, transient electroluminescence was used to study exciton dynamics. Only slow decay, coming from the energy transfer of triplets from exciplex emission, was observed during turn-off transient which proved the TTAUC emission mechanism.
89.3 % increase in operation lifetime was achieved in a blue TTA-OLED by introducing 10% assistant host (AH) material in the emitting layer. By observing the exciton diffusion length, hole-only device, electron-only device characteristics, and TrEL and photoluminescence spectra before and after device aging at constant current, we characterized the function of AH in this OLED.

摘要 I
Abstract II
List of Figures VIII
List of Tables XXII
Chapter 1 Introduction 1
1.1 Overview 1
1.2 Introduction to OLED 1
1.3 TTA OLED 2
1.4 Exciplex OLED 5
1.5 Triplet Triplet Annihilation upconversion 7
1.6 Degradation mechanisms of OLED 16
1.7 Transient electroluminescence of OLED 23
1.8 Measurement of exciton diffusion length 27
1.9 Motivation 28
1.10 References 29
Chapter 2 Experiment 33
2.1 Introduction 33
2.2 Device fabrication 33
2.3 Measurement systems 34
2.3.1 Setup of brightness-current density-voltage (BJV) system 34
2.3.2 Spectrum decomposition of dual-band emission 36
2.3.3 Transient electroluminescence (TrEL) setup 36
2.3.4 Steady-state photoluminescence 38
2.3.5 Steady-state photoluminescence degradation measurement 39
2.4 References 42
Chapter 3 Triplet-triplet Annihilation Upconversion Blue Organic 43
3.1 Introduction 43
3.2 Steady state B-J-V characteristics of OLEDs 44
3.2.1 OLEDs based on different HTL-ETL combinations 44
3.2.2 Layer thickness tuning for lowering turn-on voltage of TTAUC OLED 53
3.2.2.1 Optimization of TTAUC device by increasing BPhen thickness 70
3.2.3 Optimization of four devices based on different HTL-EML combinations for lowering turn-on voltage 72
3.3 Transient electroluminescence analysis of OLED 78
3.3.1 TREL of NPB/ADN/BPhen blue TTA OLED with different forward bias, turn-on pulse width and turn-off time interval
78
3.3.2 Effect of reverse bias on NPB/ADN/BPhen blue TTA OLED
83
3.3.3 TREL of m-MTDATA/m-MTDATA:BPhen/BPhen yellow exciplex OLED with different forward bias, turn-on pulse width and turn-off time interval 84
3.3.4 Effect of reverse bias on m-MTDATA/m-MTDATA:BPhen/BPhen yellow exciplex OLED 92
3.3.5 TREL of m-MTDATA/m-MTDATA:ADN/BPhen yellow exciplex OLED with different forward bias, turn-on pulse width and turn-off time interval 96
3.3.6 Effect of reverse bias on m-MTDATA/m-MTDATA:ADN/BPhen yellow exciplex OLED 106
3.3.7 TREL of m-MTDATA/ADN/BPhen TTAUC OLED with different forward bias, turn-on pulse width and turn-off time interval
109
3.3.8 Effect of reverse bias on m-MTDATA/ADN/BPhen TTAUC OLED 115
3.3.9 Effect of reverse bias on m-MTDATA/m-MTDATA: BPhen/BPhen OLED and m-MTDATA/m-MTDATA:ADN/BPhen OLED (thick devices) 117
3.3.9.1 Effect of reverse bias on m-MTDATA/m-MTDATA:BPhen/BPhen OLED (thick devices) 118
3.3.9.2 Effect of reverse bias on m-MTDATA/m-MTDATA:ADN/BPhen OLED (thick thickness) 122
3.3.10 Turn-off dynamics of exciplex emission and blue emission comparison between various devices 126
3.4 References 131
Chapter 4 Elongation of Operation Lifetime for Blue Triplet-triplet Annihilation Organic Light-emitting Diode
133
4.1 Introduction 133
4.2 B-I-V characteristics of blue TTA OLED 133
4.3 Hole-only and electron-only device 135
4.4 Device recombination zone probing 137
4.5 Exciton diffusion length measurement 145
4.6 Turn-off dynamics of TREL with time aging 152
4.7 Photoluminescence degradation measurement 156
4.8 References 161
Chapter 5 Summary 162

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