高分子發光二極體(PLEDs)分別自陽極及陰極注入電洞及電子，傳輸至發光層再結合形成激發子而放出不同光色。若要達到高效率的發光，電洞及電子在發光層內的平衡就相當重要，然而，元件中電洞的傳輸速度通常比電子來得快而造成載子的不平衡，為了解決此問題發展出多層元件來改善電子注入、傳輸能力；傳統上多層元件以真空蒸鍍的方式製備，但由於操作需在高溫下進行，製備環境要求甚嚴且成本較高。故本研究設計並合成出可利用濕式製程的電子傳輸材料，在提高元件效率的同時，亦能降低製備成本。
本研究成功利用Suzuki Coupling Reaction合成出側鏈含有苯并咪唑及二乙醇胺基基團的聚亞苯(PMBI-NOH、PPBI-NOH)，並將其導入多層元件作為電子傳輸材料，以核磁共振光譜(1H NMR)、元素分析儀(EA)、紅外線光譜儀(FTIR)鑑定其結構，並分析其熱性質、光學性質、電化學性質、膜態及元件特性。由於主鏈為剛硬的聚亞苯，使兩高分子擁有高熱裂解溫度(Td > 300 oC)、高玻璃轉移溫度(Tg > 100 oC)；PMBI-NOH及PPBI-NOH的薄膜態吸收光譜皆有兩個吸收峰，而薄膜態螢光放光光譜分別在421 nm及424 nm；從循環伏安法可以得到PMBI-NOH及PPBI-NOH之LUMO/HOMO能階分別為-2.58/-5.61 eV及-2.70/-5.70 eV，由於側鏈含有苯并咪唑及二乙醇胺基基團可以降低LUMO及HOMO能階，不僅能讓電子更容易進入發光層，同時也具有電洞阻擋的特性。以旋轉塗佈法將PMBI-NOH及PPBI-NOH塗佈於發光層(Super Yellow: SY)上作為電子傳輸層(ETL)製備多層螢光元件(ITO/PEDOT:PSS/SY/ETL/LiF/Al)，PMBI-NOH由於在共溶劑中的溶解度差和表面膜態不好，導致無法有效地改善元件的表現；在無加入電子傳輸層之元件最大亮度為8,690 cd/m2，最大電流效率為2.78 cd/A，而加入PPBI-NOH作為電子傳輸層之元件，最大亮度提升至12,881 cd/m2，最大電流效率亦提升至10.94 cd/A。
研究結果顯示，作為元件之電子傳輸層的應用上，PPBI-NOH的表現勝過PMBI-NOH，除了溶解度的因素之外，加入PPBI-NOH可以使電洞及電子在發光層中更加平衡；PPBI-NOH不僅能改善電子注入/傳輸的能力，也具有卓越的電洞阻擋特性，大幅提升元件之表現，並且能以濕式製程的方式塗佈製作，在電子傳輸材料的應用上具有發展潛力。

Charge balance is a crucial factor in enhancing device efficiency of polymer light-emitting diodes (PLEDs). An electron-transporting layer is inserted in multilayer PLEDs to solve the problem of low electron mobility. Electron-transporting materials containing electron-withdrawing groups and polar side chains effectively enhance device performance. In this study, two new electron-transporting polyphenylenes PMBI-NOH and PPBI-NOH, linked via meta- and para-position respectively, have been designed and synthesized to be applied as electron-transporting layer or hole-blocking layer. Both polymers possess excellent thermal stability (Td > 300 oC, Tg > 100 oC) due to their rigid backbones. In addition, their LUMO (~ -2.70 eV) and HOMO (~ -5.70 eV) levels are effectively lowered by the benzimidazolyl and diethanolamino groups, resulting in improved electron-injection and hole-blocking capabilities. Multilayer yellow emitting PLEDs with a configuration of ITO/PEDOT:PSS/SY/ETL/LiF/Al were fabricated by spin-coating process. The maximum luminance and maximum current efficiency of PPBI-NOH-based device were 12,881 cd/m2 and 10.94 cd/A respectively, superior to the performance of PMBI-NOH-based device (4,938 cd/m2, 3.70 cd/A) and the device without ETL (8690 cd/m2, 2.78 cd/A).

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