週期性奈米環形槽結構於氫化非晶矽薄膜太陽能電池之應用

Abstract

本研究藉由自組裝聚苯乙烯奈米球形成規則排列的單層膜當作遮罩，利用奈米球微影術製作週期性奈米環形槽結構，作為氫化非晶矽薄膜太陽能電池之背反射電極。週期性奈米環形槽背反射電極能增加光的散射，同時產生表面電漿子共振使近場增強，進而提升氫化非晶矽薄膜太陽能電池之短路電流密度。實驗主要分為三部分，第一部分選定結構的深度為100 nm，改變奈米環形槽結構的週期，探討其對元件效率的影響；第二部分把環形槽週期固定於效率最高的條件後，我們再改變奈米環形槽結構的深度，探討結構深度和效率間的關係；第三部分將針對週期為500與1000 nm的環形槽結構，調變氧化鋅鋁厚度，得到最佳的背反射電極條件。 環形槽週期影響背反射電極的霧度頻譜，霧度會隨著週期增加而提升，進而增加太陽能電池效率。週期固定於最高效率的環形槽週期1000 nm後，接著我們比較三種不同環形槽深度，發現環形槽深度對效率的影響並不顯著。調變氧化鋅鋁厚度的實驗中，隨著氧化鋅鋁薄膜厚度減少，耦合至吸收層的電磁波電場強度增強，進而提升短路電流密度。在環形槽週期為1000 nm、深度為100 nm的情況下，相較於濺鍍沉積氧化鋅鋁厚度115 nm的背反射電極，在原子層沉積氧化鋅鋁8 nm的條件下，電池效率增加了12.9% (5.66%→6.39%)。

A self-assembled close-packed monolayer of polystyrene (PS) spheres was deposited as a mask to fabricate periodic anti-ring structures using nanosphere lithography (NSL) technique. The periodic anti-ring structures were employed as back reflectors in hydrogenated amorphous (a-Si:H) silicon thin-film solar cells; this arrangement raised the scattering effect and induced the surface plasmon polariton to enhance the near-field electromagnetic wave intensity, which thereby improved the photocurrent density and efficiency of the solar cells. The effects of periods and depths of anti-ring arrays, as well as the AZO (Al-doped ZnO) thicknesses on the performance of hydrogenated amorphous silicon thin-film solar cells were investigated. The haze was dependent on the periods of the anti-ring arrays. A larger period led to a higher haze for the back reflector, resulting in better solar cell efficiency. With a fixed period of 1000 nm, solar cells with anti-ring arrays of various depths were fabricated. However, no significant difference in efficiency was noted. Next, the performance of solar cells with anti-ring arrays of various AZO thicknesses was examined. As the AZO thickness decreases, stronger electric field intensity was coupled into the absorption layer, leading to the increases of the photocurrent density and cell efficiency. With an anti-ring back-reflector of 1000 nm in period and 100 nm in depth, the solar cell with ALD-deposited 8-nm-thick AZO reached an efficiency of 6.39%—an improvement of 12.9% compared to that with sputter-deposited 115-nm-thick AZO layer.