本研究中採用DCzPPy為主體材料，透過改性合成兩種含吡啶的雙極性主體材料DDMACPy和DTPAPy，其具有高三重態能量。我們發現DDMACPy（5.5 eV）和DTPAPy（5.6 eV）的HOMO能階較DCzPPY（5.9 eV）的HOMO能階淺，可改善自電洞傳輸層PEDOT：PSS（WF=5.1 eV）的電洞注入；這些主體材料用於藍色有機發光二極體（OLED，而TADF發光體中的天藍光發光層將使用DAMC-TRZ作為客體材料。DDMACPy基體元件顯示它們具有最大外部量子效率（EQEmax），電流效率（CEmax）和功率效率（PEmax）分別為21.02％，53.1 cd A-1和44.0 lm w-1（CIE（0.17, 0.42））。進一步將紅色磷光發光客體 Ir（dpm）PQ2和黃色磷光發光客體PO-01-TB發光體摻進天藍光發光層，結果顯示TADF-磷光體混合白色OLED（ T-P WOLED）在CIE（0.35,0.44）狀態下具有優異的EQEmax、CEmax和PEmax，數據分別為17.93％、48.7 cd A-1和44.5 lm w-1，且天藍光和白光OLED均顯示在1000 cd m-2（EQE1000）亮度下，外部量子效率分別為穩定的18.73％和16.24％。

Two pyridine containing bipolar host materials with high triplet energy, 9,10-dihydro-9,9-dimethyl-10-(3-(6-(3-(9,9-dimethylacridin-10(9H)-yl)phenyl)pyridin-2-yl)phenylacridin (DDMACPy) and N-(3-(6-(3-(diphenyl amino)phenyl)pyridin-2-yl)phenyl)-N-phenylbenzenamine (DTPAPy), are synthesized from modifying the commonly adapted host material 2,6-bis(3-(9H-carbazol-9-yl)phenyl)pyridine (DCzPPy). The HOMO levels of DDMACPy (5.5 eV) and DTPAPy (5.6 eV) are found to be shallower than that of DCzPPY (5.9 eV) that leads to the improvement in hole injection from the hole transport layer PEDOT:PSS (WF = 5.1 eV). These host materials are used in the emitting layer of blue organic light-emitting diode (OLED) with the sky-blue TADF emitter, 9,9-dimethyl-9,10-dihydroacridine-2,4,6-triphenyl-1,3,5-triazine (DAMC-TRZ), as the guest. The DDMACPy-based device shows the highest performance among them with the maximum external quantum efficiency (EQEmax), current efficiency (CEmax) and power efficiency (PEmax) of 21.02%, 53.1 cd A-1 and 44.0 lm w-1 at CIE (0.17, 0.42), respectively. By further doping with the red emitting phosphor iridium(III) bis(2-phenylquinoline)(2,2,6,6-tetramethylheptane-3,5-ionate) [Ir(dpm)PQ2] and yellow emitting phosphor iridium(III) bis(4-(4-t-butylphenyl) thieno[3,2-c]pyridinato-N,C20 )acetylacetonate (PO-01-TB) emitters into the sky-blue emitting layer, a TADF-phosphor hybrid white OLED (T-P WOLED) is obtained with excellent EQEmax, CEmax and PEmax of 17.93%, 48.7 cd A-1 and 44.5 lm w-1 at CIE (0.35, 0.44), respectively. Moreover, both sky-blue and white OLED show the low efficiency low-off with external quantum efficiencies at the brightness of 1000 cd m-2 (EQE1000) 18.73% and 16.24% respectively.

Chapter 1. Preface 1
1-1. The development of organic light-emitting diodes 1
1-2. Fluorescence and phosphorescence principles 2
1-3. Fluorescent, phosphorescent and thermally activated delayed fluorescent emitters 4
1-4. Energy transfer 7
1-5. Host material for solution process organic light-emitting diodes 10
Chapter 2: Literature reviews 12
2-1. Bipolar small molecules host materials for OLED 12
2-2. Small molecules host materials for solution-processed blue TADF-OLED 16
2-3. Small molecules host materials for solution processed TADF and hybrid WOLEDs 20
2-4. Literature analysis 23
Chapter 3: Methods 25
3-1. Chemicals 25
3-2. General measurement and characterization 26
3-3. Synthesis 27
3-3-1. Synthesis DCzPPy 27
3-3-2. Synthesis DDMACPy 28
3-3-3. Synthesis DTPAPy 30
3-4. Device fabrication and measurement 32
Chapter 4: Results and discussion 33
4-1. Physical and optical properties of host materials 33
4-1-1. Ultraviolet-visible (UV-Vis) 33
4-1-2. Photoluminescence (PL) 34
4-1-3. Phosphorescence 35
4-1-4. Cyclic voltammetry (CV) 36
4-1-5. Thermal properties of host materials 37
4-2. DFT calculation 38
4-3. Hole only device for hole mobility 39
4-4. OLEDs charaterizations 41
4-4-1. Sky-blue OLEDs charaterizations 42
4-4-2. Searching for the optimal thickness of electron transport layer 45
4-4-3. Hybrid white OLED 50
4-5. Conclusion 56
Chapter 5: References 57

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