一、共軛高分子暨小分子多層結構PLED元件之研究 二、巰基乙醇取代聚苯胺於PLED及OLED應用之研究

劉吉雄(Ji-Xiong Liu)

指導教授 ： 韓建中

國立清華大學/理學院/化學系/博士(2007年)

摘要

高分子膜厚攸關PLED元件的EL光色與光電效能，因此我們研發出一套獨特且實用性高的『具有即時監控特性的高分子膜厚之非破壞性量測方法』以量測並監控元件製程中使用的共軛高分子薄膜厚度及塗佈均勻性；其程序為：先建立該高分子的厚度－吸收度關係式，然後透過簡單的吸收光譜量測便可精準地得知高分子膜厚。
奠基於上述的厚度量測方法，首先，我們可以得知相對精確的膜厚資訊；再者，我們可以研發出適合EL高分子的厚度控制方法；第三點，套用於高分子暨小分子多層PLED元件（簡稱ML-PLED）製程中，我們可以得知EL光色、元件效能與有機層厚度比率、陰極種類的關係。我們選擇MEH-PPV/Alq/MgAg做為ML-PLED元件的基本結構，利用上述程序系統化地研究有機層厚度比率、電極種類與元件效能及EL光色的關係；由研究的結果得知電子與電洞的注入與傳輸之平衡是效能及光色的決定因素，據此進一步提出一個適合ML-PLED的簡單通則，以預測其最佳化的厚度比率與其比值如何隨電極材料變化的關係。然後增加一層電洞阻擋層並運用電流退火效應可以製得高效能的ML-PLED，其中一個元件【ITO/MEH-PPV(~45 nm)/TPBI(10 nm)/Alq(30 nm)/MgAg】的最大亮度將近22000 cd/m2，外部量子效率達到1.2 ％。
經由同步還原與取代反應合成具有巰基乙醇取代基之聚苯胺（Pan-MEA）應用於元件製作，可以有效提高OLED的效率及亮度；Pan-MEA側鏈的醇基與ITO具有較佳的親和性，聚苯胺主鏈則與有機化合物的親和性高，ITO/Pan-MEA/organic形成契合的接觸面，可以提升電洞注入能力，進而提高效能。然而，此聚苯胺衍生物對於PLED效能的提升並不明顯，我們認為後續的EL高分子溶液於旋轉塗佈製程時，可能將Pan-MEA薄膜部分溶解以致降低其原本修飾接觸面的功能；使用硫代醋酸做為交聯劑可將Pan-MEA的主鏈連結成三度空間結構，聚合物的溶解度大幅下降，同時保有高分子共軛性的完整，應用於ML-PLED可達甚高的元件效能，其中一個經此方法處理後之元件【ITO/Pan-MEA(2 nm)/ MEH-PPV(~45 nm)/TPBI(10 nm)/Alq(30 nm)/MgAg】的最大亮度超過35000 cd/m2 ，就我們目前所知的文獻中，這是MEH-PPV的PLED元件中的最高亮度；此外，元件效率很高，其中外部量子效率達到1.88 %，發光效率達到6.31 cd/A。
由於OLED與PLED的元件效能與其相鄰材料層間的能階匹配具有很大的關聯性，因此我們發展出一個可以適用於金屬與有機化合物功函數量測，而且信賴度高的方法； 根據目前的研究結果，於XPS的『內建電力模式』量測二次電子能譜的功函數，精確度可以達到0.03 eV。結合XPS的高度化學鑑定能力與功函數量測技術，我們已經初步地得到若干ITO玻璃的處理條件與功函數的關係，控制ITO電極功函數的技術對於OLED及PLED產業幫助甚廣。此外，XPS設備配有單色光器並配合適度的操作參數，可以取得高解析度的價帶層之光電子能譜，由此可得知有機物的HOMO能階；輔以功函數量測、靈敏的表面化學分析能力，應該可以進一步建立起元件的電子能帶結構，這對元件發光、消光機制及效能改進的影響深遠，值得繼續深入探討。

關鍵字

高分子發光二極體 ； 電激發光

並列摘要

The electroluminescent and electric-optical properties of PLED devices are highly dependent on the film thickness of conjugated polymers, therefore it’s very important to establish an efficient and rapid method to obtain the true thickness of polymer film. We have successfully designed and demonstrated an unique and practical way of “non-destructive measurement method for polymer thickness” to measure the average thickness and to monitor the uniformality of the coated conjugated polymer film used in the device. As long as the thickness and absorbance relationship, expressed as a regression equation, for the employed polymer is established, we can directly obtain the precise information about the thickness and uniformality of polymer film by simply measuring its UV-vis spectrum.
Based on the “non-destructive measurement method” mentioned above, we have developed methods to obtain the coating with the desired thickness of EL polymers, and used the methods to prepare multi-layer PLED (ML-PLED) devices. In this dissertation, we have established a general guide for gaining the device with the desired thickness ratio having the optimum device performance for a given electrode material. In the case of MEH-PPV/Alq, where the polymer and small molecule materials are both EL active layers, we have found that the EL color is also sensitive to the thickness ratio of MEH-PPV/Alq layers and the employed cathode material. By using optimal thickness ratio, plus an additional hole blocking layer, together with an electrical annealing treatment, one of our ML-PLED devices with the structure of ITO/MEH-PPV(~45 nm)/TPBI(10 nm)/Alq(30 nm)/MgAg has gained a high luminescence of ~22,000 cd/m2, and an external quantum efficiency of ~1.2 ％.
We have further applied an ultrathin layer of Pan-MEA, a very unique derivative of polyaniline synthized via the concurrent reduction and substitution method, to the optimal device mentioned above for modifying the surface of the ITO electrode. With the presence of the Pan-MEA thin layer, the performance of OLED devices were much improved, while the improvement on PLED devices were not as significant. We believe that it is due to the partial dissolution of Pan-MEA film happened during the spin-casting process of the subsequent EL polymer solution, e.g., MEH-PPV/p-xylene solution. The treatment of Pan-MEA layer with the crosslinking agent thioacetic acid helps undo the “partial dissolution problem” of Pan-MEA, and meanwhile maintains the 3-D π-conjugation network of Pan-MEA. Here, we have obtained a highly efficient ML-PLED device with the structure of ITO/Pan-MEA(~2 nm)/MEH-PPV(~45 nm)/TPBI(10 nm)/Alq(30 nm)/MgAg/Ag, having a high luminescence of >35,000 cd/m2 and a high external quantum efficiency of 1.88 ％To our knowledge, this is the brightest PLED device of MEH-PPV.
In this dissertation, we have also developed a reliable method for measuring the work function data of both metals and organic compounds based on a high resolution XPS (PHI Quantera), with a measurement error of less than 0.03 eV.

並列關鍵字

PLED ； EL

參考文獻

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