奈米金屬透明電極於有機薄膜太陽能電池之發展與應用

Abstract

在本論文中，我們提出了兩種類型的奈米金屬透明導電電極-金屬薄膜和奈米線，藉由光散射和電漿增強吸收的協同效應來有效提升含有非氧化銦錫(ITO)透明電極的有機太陽能電池之功率轉換效率。我們也把具有波紋形狀的金屬表面之背反射光電極和基於多層架構的前入射光電極整合在一起。 在基於多層結構的金屬薄膜之實驗中，發展由奈米多孔銀薄膜和氧化鉬所組成的透明電極做為陽極，具有低成本、大面積加工和可室溫製程的優點。在熱蒸鍍過程中，藉由控制膜厚和鍍率來製作出高密度奈米多孔銀膜。當銀膜的厚度為10奈米和每秒5埃米的鍍率，氧化鉬/奈米多孔銀/氧化鉬的多層結構得到約為9 Ω sq-1的片電阻和70%的穿透度。相較於ITO陽極，奈米多孔陽極/SubPc/C60/BCP/Al的元件有增強表面電漿吸收和高填充因子的特性。雖然多層結構金屬薄膜的穿透度低於ITO，但元件可達到3.45%的功率轉換效率，仍可媲美ITO元件的效率。 在金屬奈米線的實驗中，我們發展由奈米銀線和過氧聚鈦酸(PPT)所組成的可溶液法製備的透明電極來提升有機太陽能電池的轉換效率。透過來自PPT的非晶氧化鈦所形成的互連層可大幅提升多層銀線的光電特性。銀線和氧化鈦所形成的複合膜可達到92.14%的平均穿透率和16.01 Ω sq-1的片電阻。結合複合膜和P3HT:PC61BM混合層之有機太陽能電池的效率是使用ITO電極之元件效率的1.45倍。光學模擬證實其效率提升可歸因於增強的近場吸收和大量的入射光散射，其源自於銀線和氧化鈦形成核殼奈米結構之隨機性。 在電漿輔助奈米結構化反射電極的實驗中，我們發展出一種奈米結構化背反射電極來提升搭配有氧化鉬 (10 奈米)/銀 (10 奈米)/氧化鉬 (25 奈米)為透明電極之上入光式元件的效率，該反射電極由聚苯乙烯奈米球模板所製備出的奈米碗型奈米洞二維陣列所構成。該高效率透明電極在波長550奈米的穿透度為88.05% 和片電阻為5.93 Ω sq-1，可達到484極高的優值。結合電漿輔助背電極和P3HT:PC61BM混合層，元件效率可由只用平面式背電極的2.91%提升到3.35%。我們把效率提升歸因於背反射光的大量散射和在奈米洞附近增強的近場吸收。 總結，根據以上的結果，覆蓋介電質的銀奈米線和由介電質及金屬層組成的三明治結構證實可優秀的取代ITO。此外，奈米金屬透明電極對於快速的發展既輕便、可撓且透明的光電元件有很大的開發潛力。

In this dissertation, we propose two kinds of transparent conductive electrodes based on metallic nanomaterials, such as metal thin films and nanowires, to efficiently improve the power conversion efficiency of organic soar cells with indium-tin-oxide-free (ITO) window electrodes by the synergetic effect of light scattering and plasmon-enhanced absorption. We also integrate a light-reflective back electrode featuring a corrugated metal surface with a multilayer-based light-incident front one. In multilayer-based metallic thin films, a transparent electrode consisting of nanoporous silver thin film and molybdenum oxide was developed for transparent anode with advantages of low cost, large-area processing and room-temperature fabrication. High density nanoporous silver film was fabricated by controlling thickness and deposition rate during thermal evaporation. With silver thickness of 10 nm and 5 Å s-1 deposition rate, the MoOx/nanoporous Ag/MoOx multilayer structure achieved ~ 9 Ω sq-1 sheet resistance and ~70% transparency. Compared to the ITO anode, the nanoporous anode/SubPc/C60/BCP/Al photovoltaic device has an enhanced surface-plasmon absorption and a higher fill factor. Although its transparency is lower than ITO, the nanoporous anode achieved 3.45% power conversion efficiency, comparable to ITO-based devices. In metal nanowires, solution-processed transparent electrodes made from silver-nanowires and peroxo-polytitanic (PPT) acid gel were developed for enhancing efficiency of organic solar cells. The electronic and optical properties of multilayer silver nanowires were significantly improved through the interconnection layers of amorphous titanium oxide (TiOx) from PPT acid gel. The AgNW-TiOx composite film showed averaged 92.14% optical transmittance with only 16.01 Ω sq-1 sheet resistance. Combining the transparent electrodes with poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PC61BM) blend, the efficiency of organic solar cells was 1.45 times of devices using ITO electrode. Optical simulations verified that the improvement was attributed to the enhanced near-field absorption and substantial scattering of incident light resulted from the random nature of the AgNW-TiOx core-shell nanostructure. In plasmonic-assisted nanostructured reflective electrodes, nanostructured back reflective electrode with nanobowl-shaped 2D nanohole arrays made from polystyrene (PS) nanosphere template was developed for enhancing efficiency of top-illuminated organic solar cells with MoOx (10 nm)/Ag (10 nm)/MoOx (25 nm) stacks as transparent electrode. The high-performance top electrode with a transmittance of 88.05% at 550 nm and a sheet resistance of 5.93 Ω sq-1 reached an extremely high figure of merit (