高極性分子在表面自組裝單分子層之結構排列及表面性質之研究

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题名:	高極性分子在表面自組裝單分子層之結構排列及表面性質之研究
作者:	吳筑曄;Wu, Chu-Yeh
贡献者:	化學學系
关键词:	自組裝單分子薄膜;亞磷酸;有機發光二極體;反射式紅外線光譜
日期:	2018-08-02
上传时间:	2018-08-31 11:34:18 (UTC+8)
出版者:	國立中央大學
摘要:	本實驗室過去的研究顯示具有高分子偶極性的CF3Bn2CH2SH和F5BnCH2SH分子以某特定比例混合在金表面形成的單分子層，其吸附密度比單一成分形成之單分子層高並提升功函數。因此本實驗中，我們延續之前在金上的結果，期望在鋁及ITO上能藉由利用不同長度間隔基的分子將會互相排斥的極性官能基錯開，或透過缺電子的苯環和多電子的苯環互相吸引或減低排斥，以反射紅外光譜、XPS、電化學、功函數等研究分子在表面上排列與鍵結的情形。結果顯示使用相同官能基的亞磷酸分子CF3Bn2PA和F5BnPA修飾在鋁的表面時，並沒能因此造成分子間距離靠近而提升功函數，推測因為亞磷酸基團體積較龐大，需要更強的吸引力才能使分子靠近。因此另外合成4FPyPA，相較於F5BnPA苯環更缺電子，與CF3Bn2PA組成混合自組裝分子薄膜時，確實能使吸附密度上升，然而功函數並未因此有提升跡象，可能原因在於4FPyPA吸附在鋁上的功函數與CF3Bn2PA落差太大，因此並未對提升功函數有幫助。當使用偶極矩比CF3Bn2PA更大的NO2BnPA時，因為傾斜角以及吸附密度較低的關係，功函數約與F5BnPA、4FPyPA相同，經組成混合自組裝分子薄膜後，在特定混合比例下可以造成功函數提升，然而吸附密度並沒有增加，考量膜厚推測是NO2BnPA受到缺電苯環的吸引更直立導致。將上述的各種混合單層分子組合應用於ITO基板修飾並製成純電洞元件與標準OLED元件，比較功函數與電流密度及發光效率關係。結果顯示當F5BnPA、4FPyPA與NO2BnPA搭配時，隨NO2BnPA比例增加，功函數與電流密度隨之下降，然而發光效率卻逐漸遞增，推測是此型OLED屬於為電洞注入多過電子注入者，持續增加功函數造成更多電洞注入，多餘的電洞被浪費因此電流效率下降。與CF3Bn2PA搭配之混合單層則趨勢相反，功函數增加，電流效率也增加。此現象有待更多的實驗去解釋。 ;Previous research in our lab found that mixed monolayer formed from the mixture of dipolar CF3Bn2CH2SH and F5BnCH2SH molecules on Au resulted in higher binding density than that formed from single component solution and the work function obtained from mixed layer modification was higher than that from single compound monolayer. In this thesis the mixed monolayers of related phosphonic acids with different molecular length or aromatic rings of different electrostatic characters on aluminium and ITO surface were studied by reflection absorption IR, XPS, electrochemistry, and work function, in the hope to achieve higher work function by mixed monolayer modification. The results showed that the work function was not raised by mixed monolayers of CF3Bn2PA and F5BnPA. Possibly because the phosphonic acid group is bulkier so that the inetermolecular interaction is not sensitive to the charge character. Mixed monolayers of more polar 4FPyPA and CF3Bn2PA can indeed increase the binding density but not the work function. Monolayer of more polar NO2BnPA molecule gave similar work function as F5BnPA and 4FPyPA, probably due to the tilt angle and lower surface density. When mixed SAM was formed with NO2BnPA, the work function was slightly improved in certain ratio, however, the surface density was not. Based on the thickness measurement, it is proposed that NO2BnPA monolayer becomes more perpendicular due to the attraction of electron-poor aromatic ring. Standard organic light-emitting diodes and hole-only devices with mixed monolayer-modified ITO as the anode were prepared. Correlations of current density with work function and luminous efficiency were observed. The devices with higher ratio NO2BnPA gave higher luminous efficiency with lower work function and current density. It is suggested that this device structure has excessive hole charges over the electron charges. With increasingly higher work function, more holes are injected, and more holes are wasted without recombination, resulting decreasing efficiency. However, the device with mixed SAMs of CF3Bn2PA and F5BnPA, a reversed trend was observed. Higher current density led to higher luminous efficiency. The cause is not clear.
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