利用介電泳力進行奈米金棒的排列與組裝並將其應用在太陽能電池效率的提升

Abstract

太陽能電池可以透過有效率地將太陽光轉換成電力進而提供我們無窮無盡的能源。現今以矽為基底的太陽能電池大多以單晶矽和多晶矽為主。和結晶性矽太陽能電池相比之下，非晶矽薄膜太陽能電池的成本可降低至2到5倍。然而由於非晶矽在能隙附近對於光的吸收效率並不好，所以如何提升其轉換效率便成為一個重要的議題。近年來，電漿子結構被成功利用來有效捕捉光，使更多的光進入太陽能電池，進而提升光電流。 在此篇論文中，我們成功地結合排列整齊的奈米金棒陣列在元件的主動層之上來達到光電流較換效率的提升。我們利用了介電泳力將維度為半徑20公分，且長寬比例大於20的奈米金棒排列並組裝。首先，施加交流電在先製做好具有微米間距的電極上進而產生電場，再將含有奈米金棒的溶液滴在基板上，如此一來，此電場就可以將溶液中的奈米金棒整齊的排列在微米的間距內。此在元件上層的奈米金棒陣列可以藉由捕捉光及散射的機制，使太陽光可以更有效在底下的矽基板被吸收利用，可以使外部量子效率在寬能帶的區域達到提升。在外加電壓20伏特排列得到的奈米金棒陣列，除了元件的外部量子效率提升之外，其短路電流也明顯地由原本的20.45 mA增加到33.09 mA，其轉換效率也從原本的4.22%增加到7.01%。

Solar cells are considered to provide virtually unlimited amounts of energy by effectively converting sunlight into electrical power. The most popular solar cells at present are crystal-based silicon solar cells using mono-crystalline or multi-crystalline silicon. Thin-film Si solar cells are promoted to reduce the cost of solar cell by a factor of 2-5 while the efficiency of conversion should also be substantially increased due to the poor absorbance of near-bandgap light. The plasmonic structure has emerged as a rapidly emerging new field for achieving light trapping in solar cells, leading to the enhancement of light current. In this thesis, we presented a plasmonic solar cell with AuNR arrays upon the active layer to enhance the conversion efficiency. AuNRs in 20 nm diameters with aspect ratio of 20 were assembled and aligned into an array perpendicular to the electrodes on the surface of the device using an electric field-assisted approach so called dielectrophoresis force. The aligned array of AuNRs deposited from colloidal solution onto well-defined substrates was fabricated in the presence of an AC electric field generated by micrometer spaced electrodes. The AuNRs increase light scattering and trapping in the silicon layers leading to enhancement of the external quantum efficiency. Additionally, the short-circuit current with appropriate design of electrodes is increased from 20.45 mA to 33.09 mA and the conversion efficiency is increased from 4.22% to 7.01% under the applied 20 Vpp.