金奈米粒子矽太陽能電池上之近場光電流分布

Abstract

我們利用有限元素分析法，對金奈米結構在太陽能電池上對光電轉換的影響進行實驗以及模擬分析，以散射場與穿透場的差異，分析不同波長光電流向影上的差異，解釋表面電漿共振效應在太陽能電池上的影響，並進一步利用近場調變的方式，初步量測結晶矽太陽能電池上由金奈米粒子的侷限性表面電漿共振所引起的光電流變化。 本論文先對幾種不同大小、不同幾何形狀的金奈米結構做光學場的模擬，根據幾何形狀的不同，不同奈米結構在表面電漿共振頻譜以及周圍的侷限性電場分布會有所改變，並在粒徑大小越大時，共振波長會有紅移的現象，最後經由模擬結果可知以金為材料的奈米結構基本最強的共振波段都會落在500~600 nm之間，而其中金奈米小球侷限性電場的分布較為靠近矽材料。所以我們選擇金奈米粒子為我們這次侷限性表面電漿近場量測的結構。我們利用表面固定化的方式讓直徑100 nm金奈米粒子分布在結晶矽太陽能電池表面。金奈米粒子矽太陽能電池，經由模擬太陽光照下的I-V曲線以及外部量子效率的量測，並針對金奈米粒子所造成電池光電轉換特性上的改變進行一系列的模擬分析，得到散射場與穿透場之間的相位改變，造成了金奈米粒子在不同波段上對矽太陽能電池吸收的抑制以及提升。最後我們利用近場調變光電流的量測方式，量測到了多波長(470 nm, 532 nm, 632 nm)的近場光電流分布並觀察到了由侷限性表面電漿場所造成的電流差異。

In this work, we use the finite element method to simulate the light propagation behavior around the nanostructure in different size and geometry. Absorption spectrum (resonance spectrum) and the electric field distribution is presented, the simulation results shows that the resonance wavelength of gold nanostructure always occur within 500~600nm the resonance wavelength which is the wavelength that Si has enough absorption. According to the field distribution and absorption enhancement factor of Si material, we choose the gold nanosphere to do the followed near-field measurement. Elaborate gold nanoparticle with dimensions of 100 nm were first fabricated on top of crystalline silicon solar cells using immobilization of gold nanosphere colloid. Si solar cells with gold nanoparticle were characterized under the AM 1.5G illumination condition and analyzed by external quantum efficiency measurement. From the results of simulation, the phase difference between scattered wave and transmitted wave induced different photo-electric response in silicon solar cell at different wavelength. Finally, Near-field disturbed photocurrent measurement is done in three different wavelength (470 nm, 532 nm, 632 nm). We directly observed that the localized photocurrent is related to localized electromagnetic field induced by plasmon resonance. The measurement is synchronized with a Atomic Force Microscopy (AFM) which allows for the simultaneous probing of topology and photovoltaic effects of metallic nanostructures.