臺灣博碩士論文加值系統

過去的這二十年，有機或高分子發光二極體(OLEDs, PLEDs)因為可以應用於平面顯示器或固態照明等等而受到許多關注，其發光機制為給予一偏壓，電子與電洞分別從陰極與陽極注入，並傳輸到發光層再結合後放出光。OLED元件的製作方式是以真空蒸鍍(Vacuum Thermal Evaporation)的方式成膜，製程較複雜且設備成本高，PLED則大多採用濕式製程(Solution Process)的方式成膜，有製程簡便、成本低、能應用於大面積等優點，因此能使用濕式製程成膜會是更好選擇。
元件要有高效率的表現，電子與電洞在發光層內數量的平衡相當重要，然而大部分有機材料特性，電洞的傳輸速度遠大於電子，發光層內電子與電洞數量不平衡，造成再結合比例低。解決的方法有導入電子傳輸層(Electron Injection Layer, EIL)、電子阻擋層(Electron Blocking Layer, EBL) [1]或電洞阻擋層(Hole Blocking Layer, HBL)[2]等等，其中使用電洞緩衝層(Hole Buffer Layer, HBL)(下文的HBL皆表示電洞緩衝層)將電洞的傳輸速率降低也是可以提高有機發光二極體元件效率的方法之一。
本研究所使用之化合物為張雅婷同學合成的，利用Suzuki Coupling Reaction和Schiff Base Condensation合成出主體為1,3,4-噁二唑基團與周圍導入兩個希夫鹼基團的化合物(M1)，以核磁共振光譜(1H-NMR)、基質輔助雷射脫附游離飛行質譜儀 (MALDI/TOF-MS)、鑑定其結構，分析其熱性質、光學性質、電化學性質、膜態，並將其作為電洞緩衝層應用於高分子發光二極體，測量電激發光的特性。
M1熱裂解溫度(Thermal Decomposition Temperature, Td)為264oC，熱穩定性高；M1的薄膜態螢光放光峰為560 nm，放光強度很小，因此不會影響元件本身的光色；循環伏安法觀察並計算得到M1的最高占有分子軌域(HOMO)為-5.29 eV，最低未占有分子軌域(LUMO)則是-2.46 eV，從HOMO能階得知M1具有電洞緩衝的特性。
本研究利用濕式製程的旋轉塗佈將M1作為電洞緩衝層應用於多層有機發光二極體元件(ITO/PEDOT:PSS/HBL/SY-PPV/LiF/Al )，在未應用電洞緩衝層的元件中，最大亮度為6,877 cd/m2，最大電流效率為2.23 cd/A；應用M1作為電洞緩衝層的元件中，最大亮度提高至25,693 cd/m2，最大電流效率則提升到7.84 cd/A。Y. Divayana團隊利用真空蒸鍍將電洞阻擋材料BCP導入元件結構(ITO/m-MTDATA/BCP/NPB/Alq3/Mg:Al )，應用BCP的元件最大亮度未得到提升，但最大電流效率從2.5 cd/A提升至3.25 cd/A[2]。Zhaoyue Lu團隊使用真空蒸鍍將電洞阻擋材料PBD導入元件(ITO/CuPc/PBD/NPB/Alq3/LiF/Al )，未應用PBD的元件中，最大亮度約為7500 cd/m2，最大電流效率約為1.40 cd/A；應用PBD作為電洞緩衝層的元件中，最大亮度提升至約9800 cd/m2，最大電流效率則提升到2.00 cd/A[3]。與以上兩個團隊的元件比較，本研究使用的M1在同為電洞緩衝層的應用上，無論是最大亮度或是最大電流效率都有更大幅度的提升。
由研究結果得知，以M1為電洞緩衝層，除了具有優良的電洞緩衝能力外，對於電子阻擋的能力也有提升，因此能夠使到達發光內之電子與電洞的數量更加平衡，元件的表現便大幅提升。與以上兩個團隊的元件比較，元件的表現有更明顯的提升，M1還可以使用濕式製程的方式成膜，在製程簡便和成本較低下更具有優勢，因此M1是具有發展潛力的新穎電洞緩衝材料。

Organic light-emitting diodes (OLEDs) have attracted considerable attention because of their promising applications in flat panel displays and solid-state lighting devices. Generally, organic light emitting diodes (OLEDs) are fabricated by vacuum thermal evaporation whereas polymer light emitting diodes (PLEDs) are fabricated by solution process. Vacuum evaporation leads to high cost and complicated architectures. On the other hand, the advantages of solution process are mainly low cost and large area application. In order to enhance device efficiency, charge balance is very important. In this study, we have successfully synthesized a new material M1 by the Suzuki-coupling reaction and Schiff base condensation. The M1 is composed of 1,3,4-oxadiazolyl core with two trihydroxy tert-butyl groups, capable of being applied as hole buffer layer (HBL) by solution process in PLED devices to reduce hole mobility and enhance device efficiency. The thermal decomposition temperature (Td, at 5% weight loss) of M1 was about 264oC. The HOMO and LUMO levels of M1 were -5.29 eV and -2.46 eV, respectively, as estimated from the onset oxidation and onset reduction potentials measured in cyclic voltammogram. Multilayer PLED devices [ITO/PEDOT:PSS/M1(HBL)/SY-PPV/LiF/Al] have been successfully fabricated using spin-coated M1 as hole buffer layer. The maximum luminance and maximum current efficiency of the device with the optimized thickness of M1 (14 nm) were 25,693 cd/m2 and 7.84 cd/A. This performance is superior to the device without HBL (6,877 cd/m2, 2.23 cd/A). Our results indicate that spin-coated, M1 is a potential hole buffer materials applicable in optoelectronic devices.

摘要 I
誌謝 XIII
目錄 XIV
表目錄 XVII
圖目錄 XVIII
第一章 緒論 1
1-1. 前言 1
1-2. 理論基礎 4
1-2-1. 有機材料的共軛導電特性 4
1-2-2. 螢光理論 6
1-2-3. 影響螢光強度的主要因素 8
1-2-4. 分子間激發態(Interchain Excitons)和分子內激發態(Intrachain Excitons) 11
1-2-5. 能量轉移機制 12
1-3. 元件發光原理 15
1-3-1. 光激發光 15
1-3-2. 電激發光 16
1-4. 元件結構 18
1-4-1. 單層元件 18
1-4-2. 多層元件 20
第二章 文獻回顧 22
2-1. 有機電激發光材料的分類 22
2-1-1. 電子注入/傳輸材料(EIM/ETM) 24
2-1-2. 電洞注入/傳輸材料(HIM/HTM) 25
2-1-3. 共軛高分子發光材料 26
2-1-4. 電洞緩衝材料(HBM) 28
2-2. 有機發光二極體的效率 29
2-2-1. 有機發光二極體效率之影響參數 29
2-2-2. 增進電子與電洞數目平衡的方法 30
2-3. 濕式製程 32
2-4. 希夫鹼的發現與應用 34
2-5. Suzuki-Miyaura Coupling Reaction 37
2-6. 研究動機 38
第三章 實驗內容 39
3-1. 實驗裝置與設備 39
3-2. 鑑定儀器 41
3-3. 物性與光電測量儀器 43
3-4. 實驗藥品與材料 51
3-5. 反應步驟與結果 53
3-6. 元件的製作與測量 56
3-6-1. 元件製作流程與清洗 56
3-6-2. 製備電洞注入層、電洞緩衝層、發光層、電子注入層與陰極的詳細說明 57
3-6-3. Hole-Only元件製備 58
3-6-4. 蒸鍍系統 58
3-6-5. 元件測量 60
第四章 結果與討論 61
4-1. 化合物的合成與鑑定 61
4-1-1. 核磁共振光譜(NMR) 61
4-1-2. 基質輔助雷射脫附游離飛行質譜儀(MALDI/TOF-MS) 65
4-2. 熱性質分析 67
4-2-1. 熱重分析(TGA) 67
4-2-1. 微差式掃描熱卡計分析(DSC) 68
4-3. M1光學性質分析 70
4-3-1. UV/Vis吸收光譜及PL放光光譜 70
4-4. 電化學性質分析 73
4-5. M1成膜性質分析 75
4-6. 高分子發光二極體元件特性 78
4-6-1. 元件結構與能階 78
4-6-2. M1應用於元件之電激發光性質 80
4-6-3. Hole-Only元件(HOD) 85
第五章 結論 87
參考資料 89

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