磷光有機發光二極體(PhOLEDs)是新世代平面顯示器中最具潛力的技術。由於其發光層摻雜重原子錯合物之磷光發光體，使其可同時利用單重態和三重態激子，將原本理論上內部量子效率25%提升至100%，其中濕式製程更被視為讓製程簡單化且面板大尺寸化的關鍵。但由於傳統濕式製程之高分子主體材料雖然有良好的膜態，但由於其純化不易且沒有固定之分子量，因此小分子主體材料變成主體材料之研究趨勢。而對於高效率濕式製程的磷光發光二極體而言，小分子雙極主體材料必須擁有良好的熱穩定性及膜態並同時具有極佳的載子傳輸能力以增加電子及電洞再結合，這也是目前主體材料開發之主流。
因此本研究設計並合成兩種新型的磷光有機發光二極體元件(PhOLED)之雙極主體材料(bipolar host materials) FC3O與FC4O，並以芴(fluorene)為核心(core)，鍵結親電洞之咔唑(carbazole)基團以及親電子的噁二唑(oxadiazole)基團，並利用基團數目不同，得到具有良好載子傳輸能力之雙極主體材料。由於FC3O和FC4O具有許多龐大且剛硬之基團，使其具有高熱裂解溫度(Td > 350oC)與玻璃轉移溫度(Tg > 140oC)，因此即使在退火後也擁有良好的膜態(RMS roughness < 1 nm)，使其可以成功地應用在濕式製程上。FC3O與FC4O擁有高三重激發態[ET= 2.49 eV (FC3O)及2.63 eV (FC4O)]，故將其混摻客發光體Ir(ppy)3，並成功地應用於綠色磷光元件[ITO/PEDOT:PSS/EML/BCP/LiF /Al]。而元件表現上，FC3O與FC4O最高亮度分別為9358 cd/m2及10232 cd/m2，最大電流效率分別為14.9及18.2 cd/A，遠勝於傳統濕式主體材料PVK (1500 cd/m2、4.0 cd/A)，且在高亮度1000 cd/m2下，FC3O及FC4O之電流效率仍高達12.2 cd/A (18.3% of roll-off)及17.3 cd/A (4.9% of roll-off)。這些優良之元件表現可歸因於：(1) FC3O與FC4O有良好的載子傳輸能力，展現出良好雙極材料特性；(2) 相較於PVK主體材料，FC3O與FC4O的HOMO與LUMO能階與載子傳輸層較匹配，使得載子可以有效的注入進發光層；(3) 由於FC3O及FC4O之分子結構蓬鬆剛硬且非平面性高，因此可以有效防止激發雙體與激發複合體的產生，因此FC3O及FC4O應用在濕式製程綠色磷光元件上有優良的表現。

In recent years, phosphorescent organic light-emitting diodes (PhOLEDs) have drawing attention increasingly in solid-state lighting application utilizing excitons to achieve 100% internal quantum efficiency theoretically. For wet process, polymer light-emitting diodes (PLED) are considered to be highly suitable because of good morphology but the polymeric problems are difficult purification, batch-to-batch variations and unclear molecular weight. Therefore, it is a good tendency to develop small molecular bipolar host materials possessing good charge-transporting properties and homogeneous film morphology. In this work, we successfully synthesized two new bipolar host materials FC3O and FC4O utilizing fluorene as a bridge and they possess different ratios (3:1, 4:2) of electron-transporting oxadiazolyl and hole-transporting carbazolyl moieties. The bipolar hosts revealed good thermal stability (Td > 350 oC, Tg > 140 oC) because of intrinsic bulky and non-planar structures. Homogeneous films (RMS roughness < 0.8 nm) were obtained by spin-coating process. Moreover, the HOMO/LUMO levels are closed to that of PEDOT:PSS/BCP so hole-injection/electron-injection are improved as well. In addition, multilayer green PhOLEDs with Ir(ppy)3 as dopant were successfully fabricated by spin-coating process. The maximum luminance and maximum current efficiency of FC3O- and FC4O-based device are (9358 cd/m2, 14.90 cd/A) and (10232 cd/m2, 18.2 cd/A), respectively. The performances of both are better than PVK-based one (1567 cd/m2, 4.0 cd/A).

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