聚苯硫胺衍生物之合成及其在高分子電激發光元件上之應用

Abstract

本研究成功合成出四種含有苯硫胺結構的單體，並利用強酸誘導縮合聚合方法，以CF3SO3H提供強酸環境，合成出四種共軛聚苯硫胺衍生物 poly(phenylenesulfidephenyleneamine), poly(phenylene- sulfide-alt-phenyleneaminephenyleneamine), poly(phenylenesulfide-alt- N-(4-phenoxybutylphosphonic acid)phenyleneamine), 以及 poly(phenylenesulfide-alt-N-(n-butylphosphonic acid)phenyleneamine) (P1∼P4)。P1的分子量達到1.7 × 105，而P2的分子量僅有8 × 103, 可能是由於單體M2具有兩個苯胺分子，在縮合聚合過程中導致親核芳香基集團上的電子雲密度較低，減少攻擊帶正電硫原子發生聚合反應的機會。所有高分子都能溶解於一般溶劑如THF、DMF以及DMSO中。高分子P1-P4的玻璃轉移溫度(Tg)約在83到140℃之間，而熱裂解溫度(Td)約介於240到400℃。而P3 與 P4由於在主鏈上加入了側鏈基導致熱裂解溫度及玻璃轉移溫度都較P1與P2低。 在電化學實驗中利用循環伏安計量儀(CV)得到這四種高分子的最高填滿分子軌域能階位於 -4.82 到 -5.07 eV之間，可以利用作為電洞傳輸層(HTL)材料。雙層高分子發光元件結構為 銦錫氧化物(ITO)/電洞傳輸層/發光層/鈣/鋁 。發光層選用DP-PPV或聚芴高分子衍生物。藉由在電洞傳輸材料中添加CSA (camphor sulfonic acid)作為摻雜物，元件的電流密度、亮度與效率都有明顯地改善。利用不同的電洞傳輸層製成三種不同的元件結構：(a)聚苯硫胺衍生物(P1-P4)；(b)PEDOT；(c)聚苯硫胺衍生物加PEDOT。結果顯示利用聚苯硫胺衍生物讓ITO注入電洞，PEDOT輔助電洞傳輸的元件結構(c)系列具有最佳的元件表現。以PPSA衍生物與PEDOT作為HTL層、DP-PPV衍生物為發光層的綠光元件得到最大亮度(在電壓10V達到3542 cd/m2)，而以PPSA衍生物與PEDOT作為HTL層、聚芴衍生物為發光層的藍光元件具有最佳效率為0.95 cd/A。

In this study, four kinds of novel nitrogen- and sulfur-containing conjugated polymers, i.e., poly(phenylenesulfidephenyleneamine), poly (phenylenesulfide-alt-phenyleneaminephenyleneamine), poly(phenylene- sulfide-alt-N-(4-phenoxybutylphosphonic acid) phenyleneamine), and poly(phenylenesulfide-alt-N-(n-butylphosphonic acid) phenyleneamine) (P1∼P4), were synthesized via a CF3SO3H-induced polycondensation. The polymer P1 shows the highest molecular weight. Its number-average molecular weight is as high as 1.7 × 105. The polymer P2 shows the lowest molecular weight. Its number-average molecular weight is only 8 × 103. The reason could be due to the monomer M2 containing two phenylamine units which result in decreasing the electron density of the nucleophile and lowering the nucleophilicity to attack the sulfur cation during polymerization. All four polymers are soluble in common solvents, such as THF, DMF, and DMSO. Polymers P1-P4 show glass transition temperatures (Tg) ranging from 83 to 140℃ and thermal decomposition temperatures (Td) ranging from 240 to 400℃. Both P3 and P4 exhibit much lower Td and Tg than those of P1 and P2. The reason could be due to the incorporation of the long alkyl side groups in the main chains. The electrochemical properties of these four polymers were measured by cyclic voltammetry. The energy values of highest occupied molecular orbital (HOMO) are in the range from -4.82 to -5.07 eV. It means these polymers can be used as hole-transport layers (HTL) in two-layer polymer light-emitting devices (PLEDs) with the configuration of ITO/HTL/light emitting polymers/Ca/Al. The light emitting polymers are DP-PPV or polyfluorene derivatives. By adding camphor sulfonic acid (CSA) into the HTL as dopant, the current density, brightness and efficiency of the PLED devices can be extremely enhanced. Three kinds of devices are fabricated with different HTLs: (a) PPSA derivatives (P1~P4); (b) PEDOT; (c) PPSA derivatives and PEDOT. The results demonstrate that the (c) series of devices which use both PPSA derivatives and PEDOT layers show much better performance than the others. The maximum brightness of a green device using PPSA derivatives and PEDOT as HTL and DP-PPV derivatives as emitting layer is 3542 cd/m2 at 10 V. The best efficiency (0.95 cd/A) is shown by a blue device using PPSA derivatives and PEDOT as HTL and polyfluorene as emitting layer.