在我們的實驗中，主要分成兩種結構的元件：單層元件和雙層元件(有電洞傳輸層)，然後再比較電洞傳輸層對於元件特性的影響。一開始，我們使用O2電漿對ITO玻璃基板做處理，以便於清除表面的污染微粒和增加陽極的功函數。接下來是製作元件。單層元件的結構包含ITO/PEDOT:PSS/MEH-PPV/LiF/Al，而雙層元件的結構是單層元件加上電洞傳輸層，結構為ITO/PEDOT:PSS/電洞傳輸層/MEH-PPV/LiF/Al，元件的最大亮度和效率都有所提升。然而由於MEH-PPV的材料特性並不是相當適合用於電洞傳輸，所以我們發現使用小分子的電洞傳輸材料來彌補MEH-PPV的缺點是相當好的方法。NPB在小分子有機發光二極體是相當好的電洞傳輸材料。因此，我們將NPB摻雜進雙層元件的電洞傳輸層中以便於提升MEH-PPV電洞傳輸和電子阻隔的能力。我們發現元件特性會有明顯的改善從無摻雜的雙層元件(6990 cd/m2, 0.86 cd/A) 提升到10 wt%摻雜的(6150 cd/m2, 1.21 cd/A)和30 wt%摻雜(6490 cd/m2, 1.36 cd/A)。而且驅動電壓(亮度為500 cd/m2)也從無摻雜的3.86 V 減少到10 wt%摻雜的3.22 V和30 wt%摻雜的3.06 V，以便於達到低耗能、高效能之發光元件。
最後我們也使用一些物理分析來佐證我們的改善方法。例如AFM可以用來分析兩種材料混合後對表面粗糙度的改善。結晶性的改變則是利用XRD來探討NPB對MEH-PPV分子排列的影響。總之，我們將NPB摻雜進MEH-PPV不只有表面粗糙度的改善而且還有提升薄膜的結晶性，導致有更好的電洞傳輸能力和表面接觸，進而提升整體的元件效率。

In our study, we fabricated single-layer (basic device) and bi-layer structure (with the hole transporting layer) of PLED and compared their performance. At first, O2 plasma was used to clean the surface and increased the work function of ITO in order to be matched with LUMO (LUMOEc) of organic materials. And then, we added the hole transporting layer in basic device in order to delay hole transporting, resulting in a better recombination in emitting layer. For that reason, it’s very apparent that bi-layer structure had higher luminance and current efficiency than single layer structure. The bi-layer structure was ITO-glass/ PEDOT:PSS(40 nm)/ MEH-PPV(6mg/mL, 50 nm)/ MEH-PPV(6mg/mL, 90 nm)/ LiF(1 nm)/ Al (100 nm).
However, MEH-PPV was not a suitable hole transporting material because of its lower hole mobility. So, we discovered a great way to improve this drawback, blending NPB into MEH-PPV. As we know, NPB was a useful materials in small molecular OLED for the hole transporting layer. After adding NPB into MEH-PPV as HTL, the performance was improved very obviously from non-doped bi-layer structure (6990 cd/m2, 0.86 cd/A) to 30 wt% NPB-doped bi-layer structure (6490 cd/m2, 1.36 cd/A) and turn-on voltage (500 cd/m2) was also decreased from 3.86 V to 3.06 V, respectively. Hence, we could fulfill the dream of low power consumption and high efficiency PLED.
Finally, for the purpose of affirming the mechanism of NPB-doped MEH-PPV, we used some physical analysis such AFM and XRD to discuss the change of surface and crystallization. We could see that not only the surface roughness but also the crystallization was improved by NPB-doped method. Hence, NPB-doped method was a great way to improve the hole-transporting and electron-blocking ability for polymer materials.

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