高分子發光二極體(PLED)是藉由從陽極及陰極注入電洞及電子，並在發光層中再結合進而放光。因此，載子注入及傳輸速率的平衡是影響電流效率最重要的因素。然而在大部分的有機材料中，電洞傳輸速度通常較電子傳輸速度快，造成元件發光層內的載子不平衡，也因此導致電流效率不高。因此降低電洞的傳輸速率則是讓有機發光二極體元件效率上升的有效方法之一。
本研究成功利用Suzuki coupling以及亞胺聚合反應分別合成出兩種新型的高分子(PPI-1、PPI-2)，藉由親電子性的亞胺基團(Imine Group)來改變芘(Pyrene)的載子傳導特性，使HOMO能階降低並將其導入多層元件作為電洞緩衝材料。以核磁共振光譜(1H NMR)、元素分析儀(EA)、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。兩高分子擁有高熱裂解溫度(Td > 300 oC)、PPI-2有高玻璃轉移溫度(Tg > 100 oC)；從循環伏安法可以計算出PPI-1及PPI-2之HOMO/LUMO能階分別為-5.84/-2.46 eV及-5.63/-2.42 eV。以旋轉塗佈法將PPI-1及PPI-2塗佈於電洞注入層(PEDOT:PSS)上作為電洞緩衝層(HBL)製備多層元件[ITO/PEDOT:PSS/HBL/SY/LiF/Al]，PPI-1元件與PPI-2元件最大亮度分別為19,324 cd/m2及22,401 cd/m2，最大電流效率分別為7.9 cd/A及8.0 cd/A，表現優於無加入電洞緩衝材料之元件[ITO/PEDOT:PSS/SY/LiF/Al] (10,818 cd/m2, 2.5 cd/A)。
根據研究結果顯示，作為元件之電洞緩衝層的應用上，PPI-2元件之亮度及效率優於PPI-1元件且元件色度不會偏移。總結PPI-1與PPI-2皆擁有電洞緩衝的特性，大幅提升元件之表現，並且能以濕式製程的方式塗佈製作，在電洞緩衝材料的應用上具有發展潛力。

Two new polyimines PPI-1 and PPI-2 have been synthesized by polycondensation plus Suzuki coupling reaction and applied as hole-buffering layer (HBL) to enhance emission efficiency of polymer light-emitting diodes (PLEDs). Both polymers are thermally stable (Td > 300 oC, Tg of PPI-2 >100 oC) owing to rigid pyrene backbone. Moreover, both PPI-1 and PPI-2 contain imine (azomethine) groups in main chain, which can lower the HOMO levels to improve hole-buffering ability. Multilayer PLEDs (ITO/PEDOT:PSS/HBL/SY/LiF/Al) have been fabricated using spin-coated PPI-1 and PPI-2 as HBL. Optimal maximum luminance and maximum current efficiency of the PPI-1-based device were 19,324 cd/m2 and 7.9 cd/A), whereas those of PPI-2-based device were 22,401 cd/m2 and 8.0 cd/A, respectively. Both are superior to the performance of device without the HBL (10,818 cd/m2, 2.5 cd/A). On the other hand, PPI-2-based device is superior to PPI-1-based device in terms of color purity as expressed in stable CIE coordinates. The results indicate that hole-buffer is a significant factor for efficient PLEDs and both PPI-1 and PPI-2 are potential hole-buffering materials for enhancing device performance of electroluminescent devices.

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