表面除潤摩擦形變引起之共軛高分子巨大之光電增益

Large quantum efficiency enhancement in conjugated macromolecules induced by extreme deformations from interfacial friction of dewetting

陳炳志(Bing-Jhih Chen)

指導教授 ： 楊長謀

國立清華大學/工學院/材料科學工程學系/碩士(2010年)

摘要

本文探究 poly[2-methoxy-5-((2'–ethylhexyl)oxy) -1,4- phenylene vinylene](MEH-PPV)薄膜及MEH-PPV/polystyrene (PS)混合薄膜進行除潤後所產生的發光增益。經加熱而除潤的薄膜，發光增益受薄膜厚度及除潤過程影響，最高可達 19 倍。巨大的發光增益來自除潤後的殘留薄膜,厚度為 1~5 nm，約為分子團在未受干擾下(unperturbed coil)大小的十分之一。高分子進行除潤時大規模地運動造成的摩擦力使在殘留薄膜中的 MEH-PPV被拉伸並與基材產生強大的附著力。在被拉伸的分子鏈上，exciton-phonon interaction 被抑制，使殘留薄膜的發光效率增加。殘留薄膜中 MEH-PPV的 aggregates 亦被摩擦力解開，使發光峰有約 20 nm的藍位移。 若薄膜吸收四氫呋喃或甲苯等溶劑分子，高分子被塑化，釋放薄膜中的分子鏈反彈力，在室溫下(25~30℃)下進行除潤。殘留薄膜的形成及發光增益受薄膜中殘留應力釋放及分子鏈在基材上的運動模式影響。此外，殘留薄膜的形成取決於高分子薄膜與基材間的交互作用，因此薄膜進行除潤後是否可得發光增益視基材上的矽膠層厚度而定。 我們亦實際將除潤薄膜應用於電致發光元件，展示了其在照明科技的潛力。

關鍵字

共軛高分子 ； 發光增益

並列摘要

Abstract
In this study, the dewetting-induced photoluminescent (PL) enhancement in thin films of conjugated polymers of poly[2-methoxy-5- ((2'-ethylhexyl)oxy)-1,4-phenylenvinylene] (MEH-PPV) and its blends with polystyrene (PS) was investigated. For thermal dewetting of MEH-PPV films on silicon wafer, the PL enhancement depended on film thickness and the dewetting process, but reached as large as more than 19 folds increase of the apparent luminescence. The enhancement was resulted from the formation of an ultrathin layer of residual MEH-PPV left behind on the retreated areas by film dewetting fronts. The thickness of the residual layer was about 1~5 nm, approximately equal or less than one tenth of the unperturbed dimensions of the macromolecules. Accompanied by the large PL enhancement, a blue shift around 20 nm, attributed to molecular separations in the residual layer, was observed. During the dewetting process, the large-scale frictional movements on the substrate of the film extended the sheared macromolecules and formed strong adhesion bonding to the substrate. Molecularly constrained, the conjugated polymer chains within the residual layer were restricted from exciton-phonon interactions and the non-radiative decay of the photoluminescence processes were effectively suppressed to yield the large PL enhancements.
MEH-PPV films also underwent dewetting when imbibed in a suitable solvent vapor at ambient temperature. The solvent molecules plasticized the polymer chains and mobilized the molecular mechanisms of releasing the residual stress to cause thin film dewetting. Depending on how the stress was released and how the polymer chains were dragged along the substrate, the formation of the residual polymer layer and the photoluminescent enhancement varied. In addition, since the interactions between the polymer film and the substrate played important role in the formation of the residual layer, the thickness of silicone treatment on the substrate was found to dominate the enhancement.
A light-emitting diode based on the dewetted conjugated polymer film was also successfully demonstrated, illustrating the great potential of using thin film dewetting as a novel material process method for making conjugated polymers for electroluminescence applications.

並列關鍵字

conjugated polymer ； photoluminescence enhancement

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