臺灣博碩士論文加值系統

本篇論文中包含兩個研究主題。第一個研究主題，我們與友達光電股份有限公司進行產學合作計畫，在量子點發光二極體 (quantum dot light-emitting diode, QLED) 中採用正向熟成處理，以提高元件效率表現。通過正向熟成處理，量子點 (quantum dots, QDs) 與ZnO界面或QDs層具有了更好的載子注入或傳輸能力。與未經處理的QLED相比，在短期內 (<1天) QLED的操作電壓在電流密度1.5 mA / cm2驅動下降低1.46 V，且其效率提高約3.8倍；而在經過長達20天以上的正向熟成後，元件效率更進一步地提高至約7倍。除此之外，藍光QLED中的電洞傳輸層 (hole-transporting layer, HTL) 在定電流驅動下的損壞是影響元件操作壽命的主要原因。透過脈衝驅動的方式，我們將藍光QLED的操作壽命延長了1.85倍，並且在綠光及紅光QLED中亦分別延長了1.76倍和17.22倍的操作壽命。
第二個研究主題中，我們研究以2,4,5,6‐tetra(9H‐carbazol‐9‐yl)isophthalonitrile (4CzIPN) 作為摻雜材料的高效率綠色熱活化延遲螢光 (thermally-activated delayed fluorescence, TADF) 有機發光二極體 (organic light-emitting diode, OLED)，並以9,9'-(2-(1-Phenyl-1H-benzo[d]imidazol-2-yl)-1,3-phenylene)bis(9H-carbazole) (o-DiCbzBz), 9,9',9''-(2-(1-phenyl-1H-benzo[d]imidazol-2-yl)benzene-1,3,5-triyl)tris(9H-carbazole) (o-3CbzBz), 和 9,9',9'',9'''-(3-(1-phenyl-1H-benzo[d]imidazol-2-yl)benzene-1,2,4,5tetrayl)tetrakis(9H-carbazole) (o-4CbzBz) 作為發光層 (emitting layer, EML) 的主體材料，它們是由台灣大學化學系梁文傑教授的研究群所設計及合成的。藉由4CzIPN的低摻雜濃度 (0.5％) 來抑制摻雜濃度猝熄，以及主體材料中的較長的三重態激子擴散長度，使4CzIPN在低摻雜濃度下能獲取盡可能多的三重態激子，我們得以在以o-DiCbzBz，o-3CbzBz和o-4CbzBz為主體材料中的綠色TADF OLED中分別得到了最大電流效率為88.93 cd/A，91.2 cd/A和88.34 cd/A；最大功率效率為79.99 lm/W，82.07 lm/W和79.46 lm/W；以及最大外部量子效率（external quantum efficiency, EQE）為30.3％，31.75％ 和29.44％ 的元件表現。

There are two topics in this thesis. In the first topic, we collaborate with AU Optronics Corporation and employ positive aging treatment in quantum dot light-emitting diode (QLED) for improving device efficiency. By positive aging treatment, the quantum dots (QDs)/ZnO interface and/or QDs layer were modified with better carrier injection and/or transporting ability. Compared to QLED without treatment, device voltage decreased (1.46 V at J= 1.5 mA/cm2) and efficiency increased (~3.8-times) in short term (within 1 day). After a long storage (as long as >20 days), device efficiency further improved to ~7-times higher than QLED without treatment. Besides, the degradation of hole transporting layer (HTL) in our blue QLED was the main reason for luminance loss under constant current driving. Using pulsed driving method, we extended our blue QLED lifetime with 1.85-times improvement, and also obtained 1.76- and 17.22-times lifetime elongation in green and red QLEDs, respectively.
In the second topic, we focus on the high efficiency green thermally activated delayed fluorescence (TADF) organic light-emitting diode (OLED) based on 2,4,5,6‐tetra(9H‐carbazol‐9‐yl)isophthalonitrile (4CzIPN) as the dopant material, and 9,9'-(2-(1-Phenyl-1H-benzo[d]imidazol-2-yl)-1,3-phenylene)bis(9H-carbazole) (o-DiCbzBz), 9,9',9''-(2-(1-phenyl-1H-benzo[d]imidazol-2-yl)benzene-1,3,5-triyl)tris(9H-carbazole) (o-3CbzBz), and 9,9',9'',9'''-(3-(1-phenyl-1H-benzo[d]imidazol-2-yl)benzene-1,2,4,5tetrayl)tetrakis(9H-carbazole) (o-4CbzBz) as the host materials of the emitting layer (EML), which were designed and synthesized by Prof. Man-Kit Leung’s group, Department of Chemistry in National Taiwan University, respectively. With the low dopant concentration (0.5%) of 4CzIPN for suppressing the concentration quenching, and the long triplet diffusion length in hosts for harvesting triplet excitons in 4CzIPN, the maximum current efficiency (cd/A) of 88.93 cd/A, 91.2 cd/A, and 88.34 cd/A, the maximum power efficiency (lm/W) of 79.99 lm/W, 82.07 lm/W, and 79.46 lm/W, and the maximum external quantum efficiency (EQE) of 30.30%, 31.75%, and 29.44% were achieved in OLEDs with o-DiCbzBz, o-3CbzBz, and o-4CbzBz hosts, respectively.

致謝 i
摘要 iii
Abstract iv
Contents vi
List of Figures viii
List of Tables xiii
Chapter 1 Introduction 1
1.1 Overview 1
1.2 Introduction of QLED 2
1.3 Review of efficiency improvement and lifetime elongation for QLED 3
1.3.1 Motivation 8
1.4 Introduction of OLED 8
1.5 Review of green TADF OLED with 4CzIPN as dopant 10
1.5.1 Motivation 13
Chapter 2 Experiments 14
2.1 Introduction 14
2.2 Post treatment procedure of blue QLED 14
2.3 Fabrication process of OLED 15
2.4 Luminance-current density-voltage (L-J-V) measurement 16
2.5 TrEL system 17
2.6 Absorption and SSPL measurement 18
2.7 TrPL and PLQY system 18
Chapter 3 Efficiency and Lifetime Enhancement of Blue Quantum Dot Light-emitting Diodes 20
3.1 Introduction 20
3.2 Positive aging treatment in blue QLED 21
3.3 Degradation mechanism of blue QLED with different thicknesses of HTL 27
3.4 QLED lifetime improvement under different pulsed driving 34
3.5 QLED with post treatment measured in different period 41
3.5.1 Device performances of blue QLED with and without positive aging treatment 41
3.5.2 Positive aging effect on electron-only device 50
Chapter 4 High Efficiency Green Thermally Activated Delayed Fluorescence Organic Light-emitting Diodes 53
4.1 Introduction 53
4.2 High efficiency green TADF-OLEDs with o-DiCbzBz, o-3CbzBz and o-4CbzBz as host materials 54
4.2.1 SSPL and TrPL properties 59
4.2.2 Partially doped OLED with o-3CbzBz as the host 61
4.2.3 Non-doped OLEDs with o-DiCbzBz, o-3CbzBz and o-4CbzBz 64
4.3 Optimization procedures of TADF OLED with o-DiCbzBz, o-3CbzBz and o-4CbzBz as host 67
4.3.1 Device optimization of green TADF OLED with o-DiCbzBz as the host 67
4.3.1.1 Dopant concentration optimization 67
4.3.1.2 ETL optimization 71
4.3.1.3 EML optimization 74
4.3.2 Device optimization of green TADF OLED with o-3CbzBz as the host 78
4.3.2.1 Dopant concentration optimization 78
4.3.2.2 ETL optimization 82
4.3.2.3 EML optimization 85
4.3.3 Device optimization of green TADF OLED with o-4CbzBz as the host 89
4.3.3.1 Dopant concentration optimization 89
4.3.3.2 ETL optimization 93
4.3.3.3 EML optimization 97
4.3.4 Partially doped OLED and non-doped OLED 101
Chapter 5 Summary 107
Reference 108
Appendix 113

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