電化學聚合製備 PPV 及其發光二極體之特性研究

Abstract

本研究之目的乃是利用電化學還原聚合的方法製備 Poly(p-phenylene vinylene)(簡稱為PPV)膜,進而製備PPV發光二極體,並對其特性作探討.本 實驗分別使用 p-xylyenebis(tetrahydrothiophenium chloride)和 p- xylyenebis(triphenylphosphonium bromide)兩種不同單體,定量溶在 Acetonitrile 溶劑中,以 ITO 玻璃為工作電極(陰極),對電極為白金片 ,同樣在定電壓的條件下進行電化學聚合,成功的在 ITO 玻璃上得到緻蜜 ,均勻且透明之 PPV 膜. p-xylylenebis(tetrahydrothiophenium)單體所 得到 PPV 膜平均厚度約為 2000 埃,而另一種單體所得 PPV 膜厚約為 2500 埃.分別將上述所得之 PPV 膜置入真空高溫爐中加熱,然後蒸鍍鋁電 極即可得到 Al/PPV/ITO 三明治結構之元件.由光激發光光譜(PL)及紫外 可見吸收光譜中得知,電化學所得 PPV 比傳統化學聚合有往藍位移(blue shift)的現象,也就是經電化學聚合所得之 PPV 比化學聚合之 PPV 有較 短的π-共軛鍵長度. p-xylylenebis( tetrahydrothiophenium chloride )單體所得之 Al/PPV/ITO 元件,具有良好之 Schottky diode 特性,整流比(rectification)約 100. 而以 p-xylylenebis( triphenylphosphonium bromide)單體所得之Al/PPV/ITO元件可得到 530 nm (綠光)之電激發光(EL)波長,而且也具有 Schottky diode 特性.此元 件退火(anneal)後,不但驅動電壓從原來的 13V 降至 8V ,而且整個元件 的發光面積,發光強度及發光穩定度等特性皆比未退火時有顯著的提升. The objectives of this thesis were the electroreduction polymerization of PPV from p-xylylenebis(tetrahydrothiophenium chloride) or p-xylylenebis(triphenylphosphonium bromide) as well as the characteristics of the electropolymerized PPV film and its light emitting diodes . In this study , these two kinds of monomers p-xylylenebis(tetrahydrothiophenium chloride) and p- xylylenebis(triphenylphosphonium bromide) were dissolved in Acetonitrile in controlled quantility respectively . A TN grade ITO glass was used as a working electrode at the cathode , and a platinum plate as a counter electrode at anode . Both of the two monomer solutions in the same condition were electropoly- merized at a fixed level applied voltage . It is successful to get dense , smooth and transparant PPV film on the ITO glass . The thickness of the electropolymerized PPV film from p- xylylenebis(tetrahydrothiophenium chloride) is about 2000A , and another is about 2500A . After the PPV film was heated in a vaccum oven , the PPV film on ITO glass was coated with Aluminum metal by thermal evaporation to give an Al/PPV/ITO sandwich device . Both of the electropolymerized PPVs showed a blue shift in the photoluminescence spectra and in the UV-Vis absorption spectra , compared with the PPV prepared from tranditional chemical polymerization . It meant that electropolymerized PPV had a shorter π-conjugated chain length . The Al/PPV/ITO device from p-xylylenebis( tetrahydrothiophenium chloride) have a good Schottky diode behavior with a rectification ratio of about 10-E2 . The Al/PPV/ ITO devices from p-xylylenebis( triphenylphosphonium bromide) emit a green light with a peak of 530nm in the electroluminescence spectra on applying voltages . These diodes also have a Schottky diode behavior . When these diodes were annealed , the drive voltages of the devices decrease from 13V to 8V . The light emitting area , the intensity and the stability were improved apparently compared to the unannealed device .