| 研究生: |
許榮賓 Sheu, Rong-Bin |
|---|---|
| 論文名稱: |
含發光基及噁二唑基高分子的合成與光電性質探討 |
| 指導教授: |
陳雲
Chen, Yun |
| 學位類別: |
碩士 Master |
| 系所名稱: |
工學院 - 化學工程學系 Department of Chemical Engineering |
| 論文出版年: | 2002 |
| 畢業學年度: | 90 |
| 語文別: | 中文 |
| 論文頁數: | 144 |
| 中文關鍵詞: | 高分子發光二極體 |
| 外文關鍵詞: | PLED |
| 相關次數: | 點閱:67 下載:4 |
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PLED是利用從陽極、陰極注入的電洞及電子於發光層中再結合而發光,因此電荷傳遞速率之平衡對發光效率有非常大之影響。目前應用於PLED的導電性高分子大都屬於P型半導體(電洞注入速率大於電子),由於電荷注入的不平衡,導致發光效率下降。為了提高其效率,可利用較低工作函數的金屬為陰極(如鈣)以降低電子注入發光層的能障,提升電子注入之能力,但由於低工作函數之金屬較不安定,所以仍有其困難。此外,可利用多層結構,也就是在發光層及陰極之間加入電子傳遞層,使電子更容易越過能障,增加電子注入之速率,進而提升發光效率。除了上述方法之外,亦可藉由化學合成之方法改變其結構,導入一缺電子基團來增加電子親和力,以提升電子注入之能力,所以發光層高分子的性質,可藉由分子的設計來做出適當的調整。
本研究將缺電子性的噁二唑基(1,3,4-Oxadiazole)單體分別與發光基團Iminodibenzyl以及Distyrylbenzene利用Horner-Wadsworth-Emmons反應進行縮合聚合。所合成之高分子P1、P2的玻璃轉移溫度(Tg)分別為202℃及197℃,P3、P4皆無發現玻璃轉移溫度。P1~P4的熱裂解溫度(Td)在376~390℃之間,顯示其具有極高之熱穩定性,黏度則介於0.21~0.31 dl/g。薄膜態的最大UV/Vis吸收及螢光光譜(PL)波長分別在372~459 nm及509~550 nm,而由UV/Vis起始吸收得到的譜帶間隙(Egopt)及由循環伏安法得到的譜帶間隙(Egelec)相近,介於2.26~2.60 eV。P1~P4單層元件的起始電場分別為2.5×106 V/cm、2.3×106 V/cm、3.4×106 V/cm、3.2×106 V/cm,最大亮度則為29、349、11、25 cd/m2,此時流明效率為0.006、0.04、0.002、0.005 cd/A。藉由分子量控制來降低P2中Excimer產生的機率,則最大亮度可高達1864 cd/m2,為之前的5.4倍,此時流明效率為0.22 cd/A。以MEH-PPV為電子傳送層將P2製成雙層元件,最大亮度可達574 cd/m2,為單層之1.7倍,此時流明效率為0.08cd/A。
PLED have been extensively studied recently due to their potential applications in large area displays. An optimized PLED should have efficient and balanced charge injections from both electrodes. However, most LED polymers are p-doped, so the mobility of holes is usually much greater than that of electrons. To achieve balanced charge injection, metal electrode with low work function and additional electron transporting layer have been widely employed. Besides, balanced charge injection can also be attained by suitable molecular design, i.e. introducing both electron transporting and emission units in polymer backbone simultaneously.
In this work, electron-deficient aromatic 1,3,4-oxadiazole is incorporated into conjugated polymers containing iminodibenzyl or distyrylbenzene chromophores in main chain or as pendant group. The polymers exhibit good thermal stability (stable up to 376℃ in nitrogen) and high glass-transition temperature (P1, P2). Optical properties of the polymers were investigated by absorption and photoluminescence spectra. Electrochemical properties were studied by cyclic voltammetry and the band gaps are between 2.26~2.60 V. Single layer devices ITO/Polymer/Al were successfully fabricated and the maximum brightness and luminance efficiency of the ITO/P2/Al was 349 cd/m2 and 0.04 cd/A, respectively, at 6.2×106 V/cm. The brightness and luminance efficiency attained 1864 cd/m2 and 0.22 cd/A as viscosity decreased from 0.31 dl/g to 0.20 dl/g.
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