利用複合式奈米球微影術製作對可見光具高穿透結構之研究

Abstract

當光進入兩種不同介質時會因為折射率的不同在其表面產生反射光，也因為其反射光的產生會造成能量的耗損，進而讓太陽電池的轉換效益降低許多。而在目前能源的使用趨向高效益低成本的情況下，一些光電元件如太陽能電池、有機發光二極體或顯示器的螢幕在使用上，都在尋找可以增進其使用效益的方法。從一些如飛蛾一樣的夜行性動物中，我們可以知道利用在表面製作奈米孔洞陣列的方式，可以消除較廣波段的反射藉此增加光電元件的效益。 在本研究中，我們使用一套流程，利用奈米微影術在石英玻璃基板上製作缺陷性最密堆積的奈米孔洞陣列，而所使用的是直徑為600奈米、200奈米與100奈米的聚苯乙烯奈米球；首先我們利用自組排列與介面活性劑(SDS)技術，排出缺陷性六角最密堆積的單層奈米球陣列，然後縮束奈米球使之間的空間更為寬廣並且當沉積鋁金屬的遮罩，但縮束後的奈米球會因球的高度而限制鋁金屬的厚度，隨後使用熱蒸鍍機鍍上鋁金屬當作硬質罩幕層並震盪使縮束後的球移除，可得到有奈米凹槽陣列鋁金屬的石英基板，而這樣的石英基板在CF4的電漿環境下進行活性離子蝕刻，因為活性離子蝕刻對鋁金屬與石英玻璃的差異性蝕刻速率造成奈米孔洞陣列，隨後利用”食人魚溶液”分解掉殘留的鋁金屬。經由這樣的處理週期為600奈米，200奈米與100奈米的奈米孔洞陣列深寬比可到達各為4.5、3.3與4.7，但由於光線會在奈米孔洞的繞射，進而造成抗反射效應會因為孔洞深度產生震盪性的衰退，在實驗中最佳的穿透率效果的結構是週期為100奈米的類拋物面的奈米孔洞深寬比則為4.5，並且排列完美六角最密堆積的單層奈米球陣列在同樣的參數下做抗反射表面對照穿透率。 再者，我們將抗反射基板應用在有機發光二極體元件上，決定是否能增加有機發光二極體的發光功率，研究結果顯示若我們使用最佳穿透率週期是100奈米的類拋物面奈米孔洞的基板，而它的鏡向發光效率比鈉玻璃基板增加6.4%並且積分光通量比未使用抗反射基板增益16.2%。

When light impinges two different matters, reflective light will be created by different refractive indices. It results in inevitable loss of energy or reduction of photoelectric conversion efficiency for solar cell. In the pursuit of high energy efficiency in photoelectric devices, most efforts focus on methods for eliminating or reducing the refection. Nocturnal animals, such as moths, provide inspiration that surfaces with nanocavity arrays can be used to reduce reflection in board wavelengths and enhance the efficiency of photoelectric devices such as organic light emitting diode (OLED) and solar cell. In this study, we fabricated both hexagonally close-packed (HCP) and defective hexagonally close-packed nano-scale polystyrene (PS) spheres, which have diameters of 600 nm, 200 nm, and 100 nm, on quartz surfaces to produce a “nanocavity” structure by nanosphere lithography. First, we fabricated the HCP and DHCP nanosphere arrays of monolayer by self-assembly and SDS. Next, we trimmed PS spheres to increase the spacing between nanospheres. The trimmed PS spheres are used as a mask for depositing aluminum (Al) hard mask layer, and the differences in height of trimmed spheres can vary the thickness of the Al layer. After depositing the Al layer by thermal evaporation, we removed the trimmed PS spheres. Then, the substrate with the Al hard mask was etched in CF4 plasma using reactive ion etching (RIE). Because the etching rate is different for quartz and Al, the nanocavity arrays can be generated by selective etching. The Al was then dissolved with a high-temperature acidic “piranha solution.” The aspect ratio of the nanocavity of periods in 600 nm, 200 nm, and 100 nm can reach 4.5, 3.3, and 4.7, respectively. However, since light diffracts in the nanocavity, the resulting antireflective effect can result in oscillatory decay that is dependent on the depth of the nanocavity. The best transmittance is the paraboloid-like nanocavity arrays with period in 100 nm and an aspect ratio of 4.5. Furthermore, the transmittance of antireflective surfaces with perfect HCP and DHCP nanocavity arrays and period are compared and discussed. In addition, the antireflective substrate is applied in the OLED device to have the potential to enhance the light power in OLED. In this study, when the quartz substrate of best transmittance of period in 100 nm is used for light extraction, the normal luminance shows a 6.4% increase when compared with sodium glass substrate. The integrated luminous flow can be 16.2% higher than that of pure air.