聚-(2,3-雙苯基-1,4-仲苯基乙烯)之衍生物及聚-(1,4-仲苯基乙烯)/氧化物奈米顆粒之複合材料之合成與鑑定。以複合物薄膜做為發光層之二極體光學及電性性質之研究

Abstract

本研究主要目的在於探討新穎發光高分子材料之合成及其在光電性質方面的應用。第一部份為聚-(2,3-雙苯基-1,4-仲苯基乙烯) (DP-PPV)衍生物之合成及光電性質研究。第二部份為高分子掺混氧化物奈米顆粒之複合材料之光電性質研究。

第一部份共合成出三種含液晶基側取代之DP-PPV衍生物。首先合成具有雙苯環液晶基之單體，再利用Gilch聚合法來聚合高分子。由偏微掃描卡計圖譜發現高分子具有寬廣的向列型液晶相，範圍從172℃至290℃。由熱重分析儀結果得知其具有高耐熱穩定性。高分子薄膜之紫外-可見光吸收峰範圍從361至405 nm，螢光放射峰範圍從500至540 nm。製備氧化銦錫-聚賽吩-高分子-鈣(鋁)之雙層有機發光二極體元件，其驅動電壓為11伏特，發出綠色光。最大的發光效率為0.79 cd/A。本研究亦發現高分子薄膜經定向摩擦後，具有發出偏極化光之能力，其Dichroic ratio值約為2.1。

第二部份掺混二氧化矽或二氧化鈦奈米顆粒於聚-(1,4-仲苯基乙烯) (PPV)及聚-(2-甲烷氧基-5-(2’-乙基己烷氧基)-1,4-仲苯基乙烯) (MEH-PPV)以製備高分子複合材料。在PPV複合材料方面，由紫外-可見光吸收光譜及螢光光譜得知掺混氧化矽之複合薄膜具有高藍位移，但掺混氧化鈦則只有些許差別。螢光光譜同時顯示當奈米顆粒的濃度增加時，高能肩帶(515 nm)之強度會增加。拉曼光譜顯示在含有氧化矽之複合材料中1547/1625 cm-1雙峰之強度比率會降低，但氧化鈦複合材料中則不會發生。以上結果說明氧化矽奈米顆粒會減少PPV之共軛長度，但氧化鈦奈米顆粒則否。傅立葉轉換紅外光譜顯示這兩種奈米顆粒皆能降低在PPV主鏈上碳氧雙鍵基團的產生。在MEH-PPV複合材料方面，奈米顆粒對光學性質上的影響較小，但是可以避免螢光強度快速降低，進而穩定複合薄膜。在氧化銦錫-複合物-鎂鋁之單層元件的電流-電壓特性曲線量測上，依據不同的顆粒大小及氧化物特性，具有不同的電性性質。複合物-電極接觸形態，高分子-介電顆粒接觸面，以及高分子鏈長度的改變，皆是造成元件具有不同性質的可能解釋。另外在導入MEH-PPV於奈米孔洞的研究方面，當孔洞尺寸越小，螢光放射峰的藍位移程度越大。溶劑的種類在填入過程中亦有一定影響。

The goal of this research is to study the synthesis and application of new light-emitting polymers. The first part of this study is focused on the synthesis and electro-optical properties of poly(2,3-diphenyl-1,4-phenylene vinylene) (DP-PPV) derivatives. The second part is to study the optical and electrical properties of polymer composites which contain conjugated polymer and oxide nanoparticles.

In the first part, three kinds of DP-PPV derivatives containing liquid crystalline side chains were synthesized. The monomers which contain biphenyl mesogens were polymerized via Gilch route to yield DP-PPV conjugated polymers. All polymers showed a wide range of nematic phase from 172℃ to 290℃. TGA thermogram revealed that polymers possessed high thermal stability. Thin polymer films showed the UV-vis absorption from 361 to 405 nm and photoluminescence (PL) from 500 to 540 nm. A double layer device with the configuration of ITO/PEDOT/polymer/Ca(Al) was fabricated. The device emitted green light and the threshold voltage was 11 volt. The highest luminance efficiency was 0.79 cd/A. It was also found that the preferential alignment of the polymer thin films could emit polarized light after rubbing, with dichroic ratio of about 2.1.

In the second part, composites made by incorporation of silicon oxide (SiO2) or titanium oxide (TiO2) nanoparticles into poly(p-phenylene vinylene) (PPV) or poly(2-methoxy-5-(2’-ethylhexyloxy)-1,4-phenylene vinylene) (MEH-PPV) were fabricated. For PPV composites, the UV-vis absorption and PL spectra of the composite films showed a large blue-shift with SiO2 nanoparticles, but only little difference with TiO2 nanoparticles. PL spectra also showed an increase in intensity of the high energy shoulder (515 nm) when the concentration of nanoparticles increased. Raman spectra showed a reduction of the 1547/1625 cm-1 band ratio in SiO2 composites but not in TiO2 ones. These results suggest that SiO2 nanoparticles reduced the conjugation length of PPV, while TiO2 nanoparticles did not. Fourier-transform Infrared (FT-IR) spectra showed that both types of nanoparticles reduced the formation of carbonyl groups in PPV main chains. For MEH-PPV composites, nanoparticles have small influence on their optical properties, but they can stabilize the composite films by preventing the fast degradation of PL emission intensity. Current-voltage characteristics measured in ITO-composite-MgAg diodes exhibit different electrical behaviors of the composites depending on the particle size and the nature of the oxide. The composite-electrode contact morphology, the polymer-dielectric particle contact, and the change in the polymer chain length are the possible explanations for these changes in behavior of the diodes. For the study of introduing MEH-PPV into nanopores, blue-shift of photoluminescent emission peak became larger when the pore size increased. The type of the solvent also has certain influence for the filling process.