有機電激發光元件之具電荷傳輸片段分子發光體

Abstract

本論文以設計開發OLED的發光材料為主題，並將其應用於提升OLED元件的效率表現。以下將分為兩個主要的研究方向個別簡介： (1) 雙極化主發光材料的研究 在A部份的報告中，我們設計了一個同時具電洞與電子傳輸性質的主發光材料tBu-OXDTFA，其類似樹枝狀的分子結構使其可以運用濕式製程的方式製成OLED元件。由於tBu-OXDTFA擁有較高的三重激發態，因此不僅足夠使用於藍色磷光分子，並且可以搭配適當的紅色磷光材料以製作放射涵蓋全光譜的白色OLED元件。在B部份，利用雙極化的分子材料POAPF作為紅色磷光客發光體Os(fptz)2(PPh2Me)2的主體，藉由POAPF的雙極化性質來平衡電荷於Os(fptz)2(PPh2Me)2的再結合；同時由於POAPF的分子能階也與Os(fptz)2(PPh2Me)2的能階較為匹配，可望降低一直以來困擾於鋨金屬錯合物元件較高的操作電壓，在外部量子效率提高的同時，同樣地也提高元件的功率效率。另外，利用了雙層發光層的元件結構，在分別摻混紅光與藍光的客發光體於POAPF當中以獲得白色放光的電激磷光元件，藉由POAPF的分子特性來提高外部量子效率與元件的功率效率。 (2) 具氧化三苯磷之多功能性藍光材料的研究 在這個研究主題的A部分中，我們選擇具有高效率的發光片段蒽(anthracene)來做為我們的發光中心，並且在蒽的2號位置修飾上了異丁基，另外在9與10號的位置導入具有電子傳輸特性的三苯氧磷(triphenylphosphine oxide, TPPO)而得到所設計的藍色螢光材料POAn。由分子的設計觀點，POAn分子為一個不對稱的結構，期待這樣的分子設計可以有效的將分子結晶性大幅度降低。經由如此缺電子基團的導入能夠改善原本蒽對電子注入以及傳輸的特性，並且我們發現TPPO基團與金屬電極存在著某種作用力可以便利電子由電極的注入。運用如此的分子特性於雙層的藍光元件，並同時具有高效率的元件表現。承接A部分的實驗結果，我們進一步導入可以幫助電洞注入以及傳輸的芳香胺，來得到一個具有雙極化性質的藍光材料。因此在導入了芳香胺之後，對於由陽極ITO部分注入的電洞也可以同時地獲得改善。最後所設計的雙極化藍光材料使用於單層藍光元件的結果表現也與一般的多層結構藍光元件相當。

In this thesis, the central idea is to develop materials for OLEDs, which will be utilized in the improvement of electrophosphorescence as well as electrofluorescence. The study is divided into two sub topics as following: (1) Studies of host materials with bipolar characteristics In part A, a solution-processable bipolar material tBu-OXDTFA comprising an electron-rich triphenylamine core and electron-deficient oxadiazole/fluorene peripheries was synthesized. This dendrimer-like molecule not only possesses a high triplet energy but also exhibits excellent film-forming properties upon solution processing. We achieved highly efficient blue and white electrophosphorescent OLEDs through solution processing. In the part B, we have prepared efficient red OLEDs incorporating POAPF as the host material doped with the osmium phosphor Os(fptz)2(PPh2Me)2. POAPF, which possesses bipolar functionalities, can facilitate both hole and electron injection from the charge transport layers to provide a balanced charge flux within the emission layer. In addition, we fabricated a POAPF-based white-light OLED - containing red- [doped with Os(fptz)2(PPh2Me)2] and blue-emitting [doped with FIrpic] layers - that also exhibited satisfactory efficiencies. (2) Studies of multifunctional blue emitters containing triphenyl- phosphine oxide First, we have synthesized a highly efficient blue-light emitter, POAn, which comprises electron-deficient triphenylphosphine oxide side groups appended to the 9- and 10-positions of a 2-tert-butylanthracene core. In addition to serving as an electron-transporting blue-light-emitting material, POAn also facilitates electron injection from the Al cathode to itself. Consequently, simple double-layer devices incorporating POAn as the emitting, electron-transporting, and -injecting material produce bright deep-blue lights. Furthermore, in part B, based on the advantage of triphenylphosphine oxide-based emitter, a novel bipolar blue emitter, TPAPOAn, bearing hole-transporting arylamine groups and electron-transporting triphenylphosphine oxide moieties was synthesized and incorporated into an efficient single-layer device, revealing very promising performances comparable to those of multi-layer blue-emitting devices.