雷射直寫技術應用於金屬網格軟性透明電極製作;Fabrication of Flexible, Metal-mesh Transparent Electrode Using Laser Direct Writing

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Title:	雷射直寫技術應用於金屬網格軟性透明電極製作;Fabrication of Flexible, Metal-mesh Transparent Electrode Using Laser Direct Writing
Authors:	魏楷;Wei, Kai
Contributors:	機械工程學系
Keywords:	雷射直寫;金屬網格;透明電極;選擇性雷射燒結;laser direct write;metal mesh;transparent electrode;selective laser sintering
Date:	2017-01-19
Issue Date:	2017-05-05 17:42:10 (UTC+8)
Publisher:	國立中央大學
Abstract:	本研究旨在開發雷射直寫技術應用於製作金屬網透明電極。採用自行合成之金屬離子複合物作為雷射燒結之材料，此複合物由特定比例的硝酸銀與聚乙烯醇(Polyvinyl alcohol)混合而成。當雷射光聚焦於此複合物薄膜時，複合物吸收的光轉成熱能加速離子還原，並燒結成銀奈米顆粒。給予適當之雷射光強度與平台走速，可將已還原之銀奈米顆粒燒結成銀線。雷射燒結之銀線具有良好的光學與機械性質並具有良好的導電性，可用於製作可撓式銀網透明電極。外觀部分，本研究燒結之銀線最小線寬為5 微米，尖峰高度大約為300至400奈米。而導電特性部分，使用最佳化之製程參數可達電阻率約銀塊材10倍之銀線，顯示具有良好的導電性。我們也探討5種不同雷射功率(20、40、60、80、100 mW)在5個平台走速(0.1、0.3、0.5、0.7、1.0 mm/s)時銀線之微結構變化，在本研究所探討的參數範圍內，平台走速對於銀線之品質與微結構變化影響較為顯著。接著，我們將最佳化之銀線燒結參數用於銀網製作，可獲得良好的銀網電及特性:片電阻小於19 Ω/sq而透光率大於85 %，毫不遜於市售之商用金屬氧化物電極。由於 300 – 400 奈米高之銀線，仍嫌過高，易刺穿薄膜結構，特別是有機光電元件，其有機薄膜厚度常在數十至數百奈米之間。為製作高平坦之電極，我們將附著在玻璃基板上之銀線嵌入聚酰亞胺軟板上 (Polyimide)，製作軟性崁入式金屬網電極(Flexible embedded metal mesh electrode)。我們將嵌入式電極作往復撓曲運動，以瞭解電極之電性穩定度，結果顯示試片在承受拉張應力、撓曲半徑為5 mm時，經過5000次往復撓曲後，其片電阻由原來的19 Ω/sq增至24 Ω/sq，增加約24%，仍在可接受範圍之內。最後，將雷射燒結之銀網電極應作白光有機發光二極體(White light OLED)之陰極，顯示擁有可取代傳統透明金屬氧化物電極之可能性。;This study aims to develop a laser direct writing technique for fabricating metal mesh transparent electrodes. The self-synthesized Ag-doped polyvinyl alcohol (PVA) nanocomposite is used for selective laser sintering, SLS. The nanocomposite is a mixture consisting of silver nitrate, AgNO3, and PVA. As irradiated by laser, the chelated Ag ions are first reduced from PVA and then aggregate into silver nanoparticles, Ag NPs. With appropriate operating parameters, laser power and scan speed, the reduced Ag NPs can be sintered into silver wires. The SLSed silver wires show good optical and mechanical properties and exhibit good conductivity, which can be used as flexible Ag mesh transparent electrodes. Within the current operating parameters, the sintered silver wire has a minimum line width of 5 μm, a peak height of about 300 to 400 nm and an optimum sheet resistance down to 10 times of the bulk silver. We investigate the microstructures of silver wires subjected to five laser powers of 20, 40, 60, 80, and 100 mW, respectively; and, each at five scan speeds of 0.1, 0.3, 0.5, 0.7, 1.0 mm/s. Results show that the scan speed has a more significant effect on the microstructure and quality of silver wires. Based on the relatively optimum operating condition of laser, the best sintered Ag mesh has the features: sheet resistance is less than 19 Ω/sq and transmittance is larger than 85%, no less favorable than commercial metal oxide electrodes. The height of Ag lines range from 300 to 400 nm, which is still too high, especially for organic optoelectronic devices where the thickness of organic film is often between tens to hundreds of nanometers. To fabricate a metal mesh electrode with a very low surface roughness, the sintered silver mesh on the glass substrate was embedded in a polyimide film to produce a flexible embedded Ag mesh electrode. To examine the stability in conductivity, we conduct a cyclically tensile loading test on the flexible Ag mesh substrate. Results show the sheet resistance is increased from 19 to 24 Ω/sq, an increase of 24%, after 5000 cycles of loading where the substrate is bended at a radius of curvature of 5 mm. The sintered Ag mesh electrode is finally used as the cathode of a white light OLED to demonstrate its feasibility to replace the usual transparent metal oxide electrode.
Appears in Collections:	[Graduate Institute of Mechanical Engineering] Electronic Thesis & Dissertation

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