藉由金奈米粒子提升矽太陽能電池光學吸收

Abstract

近年來研究發現金屬奈米結構能提供了數種提升薄膜太陽能電池轉換效率的方法，由於電子的產生率正比於電場強度，金屬奈米粒子在特定波段的入射光照射下，能在粒子周圍產生強烈的電場分佈。 在本論文中使用有限元素分析法模擬金奈米粒子陣列，觀察區域性表面電漿場與散射場的分佈，並且進一步分析電場如何耦合近太陽能電池，增加光學吸收。模擬的結構包含了不同直徑與粒子密度的金粒子分佈，首先先針對金奈米粒子的共振波段與矽基板的吸收頻譜進行模擬，在100奈米金粒子太陽能電池優化的結果下，與一般矽太陽能電池相比，吸收提升超過35%，但在金奈米粒子的共振波段下，金粒子抑制了整體矽基板的吸收，原因是在於矽基板中穿透場與金粒子散射場之間產生了一不為零的相位差，導致矽基板吸收減少，因此重要的金粒子的結構與設計，以達到全波段的吸收提升，接著在不同條件下利用理論計算出理論電流值，在粒子密度的優化下，光電流提升13.5%。 最後設計與架設近場調變光電流的量測方式，但目前真實元件的量測與模擬結果之間有一段差距，在此論文中會針對目前所遭遇到的問題與挑戰做深入的討論。

Metallic nanostructures provide new possibilities for the photoelectric conversion enhancement of thin film solar cells. Since the carrier generation rate is proportional to the electric intensity, a resonant plasmonic excitation can induce a strong local field around metallic nanostructures, hence increasing the optical absorption of the surrounding semiconductor. In this work, we perform a three-dimensional finite element simulation to monitor enhanced optical absorption induced by localized surface plasmon and optical diffraction of periodic gold nanospheres incorporated onto the front surface of a silicon solar cell. The calculated structures include gold nanospheres with various diameters and densities. First, the resonance peak of localized surface plasmon is tailored to match the absorption spectrum of silicon. Next, the electric field distribution is calculated explicitly, where we observe enhanced optical absorption by more than 35%, compared to the reference bare silicon. The enhancement is induced by the localized surface plasmon. However, the total absorption of the bulk silicon with gold particles is reduced at the resonance due to a phase cancellation resulting from the transmitted field and the diffracted field. It is therefore important to design the dimensions of nanospheres to achieve broadband absorption enhancement, the density of nanospheres is also optimized and achieves a maximal photocurrent conversion enhance 13.5%, which represents a compromise between forward scattering and metallic shadowing. Finally, the way to design and setup Near-field disturbed photocurrent measurement, but there’s a difference between the measurement and simulation. We are going to investigate the difficulties and challenges in this thesis.