具有高熱穩定性與多功能性可應用於藍色發光二極體之蒽衍生物

Abstract

本篇論文主要分為四個部份，前三個章節主要針對小分子蒽衍生物進行設計以及改良，第四個章節是有關於小分子磷光主發光體的性質探討。首先在第一個章節裡面，我們成功合成與鑑定出利用anthracene為主體，兩側修飾剛硬的fluorene官能基團的蒽衍生物BFAn。由於BFAn的結構剛硬且立體障礙大，導致該分子具有較佳的熱穩定性 (Td = 510 °C, Tg = 227 °C) 以及良好的成膜性質。利用BFAn做為元件主發光層，我們可以得到一個外部量子效率高達5.1% (5.6 cd/A)且CIE座標位於 (0.15, 0.12) 的深藍光發光元件。 在第二個章節中，我們報導了一種具有雙重功能性(具有電子傳輸能力與發光性質)的藍色發光材料BTAn。由於BTAn兩側導入具有優秀電子傳輸能力的官能基團benzothiazole，因此BTAn本身具有良好的電子傳輸特性。利用BTAn做為發光層以及電子傳輸層，其元件外部量子效率可以高達5.2 % (4.6 cd/A, 1.8 mA/cm2) 、 CIE座標位於 (0.14, 0.10) ，這樣的效率是十分罕見地，甚至可以媲美多層元件。 第三個章節中我們探索了一系列的蒽衍生物來研究其做為單層OLED元件的可能性，由於單層元件的效率與發光層的電子與電洞傳輸能力息息相關。為了研究這些衍生物的載子實際傳輸情形，我們製備了一系列的單層OLED元件，並且在元間中靠近陽極、陰極、以及中間位置插入DCJTB的薄膜，用來觀察其EL光譜。透過EL光譜我們可以了解其載子實際行為以及再結合區位置。利用上述實驗結果我們成功的最佳化單層OLED元件，其最大外部量子效率在電流密度1.4 mA/cm2 可以達到4.2%。 最後利用本實驗室所合成之材料TFTPA做為host，搭配清大季昀老師實驗室的Os(fptz)2(PPh2Me2)材料作為dopant來製作紅色磷光元件，同時探討其摻雜濃度與功率效率之關係。由於TFTPA在結構上具有剛硬的芴 (fluorene) 官能基團，利用fluorene在立體結構上形成的阻礙，使得Os的摻雜物 (dopant) 可以有效分散在其中，避免磷光在高濃度時產生淬熄的現象。由於摻雜濃度提高使得電荷可以透過dopant傳輸進而降低元件的操作電壓，使得元件功率效率提高 (power efficiency) 。在摻雜濃度21 wt%時，該元件具有最大亮度效率29.9 cd/A以及功率效率25.2 lm/W。即使在亮度1000 cd/m2時，其效率仍然維持在29.2 cd/A以及 22.2 lm/W。

The first section of this thesis presents the synthesis and characterization of a blue-emitting material, BFAn. Due to the presence of sterically congested fluorene groups, BFAn possess superior thermal stability (Tg = 227 °C, Td = 510 °C) and good film-forming characteristics. Organic light-emitting diodes using BFAn as the emitter exhibited an excellent external quantum efficiency of 5.1% (5.6 cd/A) with Commission Internationale de L’Eclairage coordinates of (0.15, 0.12). These values are very close to the National Television Standards Committee’s blue standard. The second section of this study reports a dual functional blue-emitting material BTAn. The end-capped benzothiazole function groups provided decent electron transporting ability. OLEDs incorporating BTAn as the emitting and electron-transporting layer exhibited a maximum external quantum efficiency of 5.2% (4.6 cd/A, 1.8 mA/cm2) with CIE coordinates of (0.14, 0.10), which was even better than typical multi-layer devices. The third section explores a series of anthracene derivatives to estimate their potential for using as the emitter in single-layer OLED devices, of which the EL performance is deeply related to the balance between the electron- and hole-transporting abilities of the emitting material. To understand the carrier behavior of these derivatives, we fabricated several single-layer devices by inserting a thin DCJTB layer in the position close to the anode, the cathode and in the middle of the devices and investigated their EL spectra. We successfully tuned the single-layer device, achieving an EL efficiency of 4.2% at a current density of 1.4 mA/cm2. The fourth section reports highly efficient red-light-emitting devices based on a fluorene-triphenylamine TFTPA host doped with an osmium phosphor, Os(fptz)2(PPh2Me)2. The sterically hindered fluorene peripheries of provided a compatible environment for the osmium dopant and alleviated concentration quenching of the phosphor at high doping levels. Increasing the doping concentration from 7 to 21 wt% decreased the driving voltage of the TFTPA-based devices dramatically, leading to improved power efficiency. The 21 wt% Os-doped device exhibited maximum luminous and powder efficiencies of 29.9 cd/A and 25.2 lm/W, combined with high efficiencies at high brightness. At 1000 cd/m2 the efficiencies remained 29.2 cd/A and 22.2 lm/W.