| Summary: | 碩士 === 國立交通大學 === 影像與生醫光電研究所 === 102 === 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.
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