利用奈米陣列結構提高HIT太陽能電池電流密度

Abstract

矽異質接面太陽電池 (Heterojunction with Intrinsic Thin Layer Solar Cell, HIT solar cell) 因兼具了低溫製程與高轉換效率的特性而受矚目。設計奈米陣列結構在HIT太陽電池上，降低入射光的反射達到光捕捉效果，有效提升HIT太陽電池的光吸收。我們利用旋塗法搭配膠體奈米球微影術(Colloidal Nanospheres lithography)，製作大面積的抗反射奈米結構應用在HIT太陽電池表面，加上非等向性蝕刻達到控制奈米抗反射結構形貌，經由嚴格耦合波分析 (Rigorous Coupled Wave Analysis, RCWA) 法，對表面奈米陣列結構不同的形貌、週期、排列方式作反射率及短路電流密度的計算並分析模擬結果。 此模擬研究中，表面奈米結構在六方最密堆積陣列 (Hexagonal array) 之空間利用率達到最大，表面結構的直徑大約等於週期一半，沉積薄膜後，結構形狀表面輪廓較不容易被完整覆蓋而形成了一層均勻的介質，表面結構相鄰之間的週期距離達到最小，覆蓋率達到最密，有較優異的抗反射效果，進一步最佳化奈米陣列結構，當高度：125nm、直徑：175nm、週期：400nm，傾斜角度750之奈米梯形截頭圓錐陣列，最終短路電流密度 36.85 mA/cm2，比表面未製作抗反射處理的 HIT太陽電池提升了14.6%，奈米陣列結構證實有優異的抗反射表現，能夠在空氣與表面奈米結構之間產生有效的梯度折射率 (gradation of refractive index)，讓更多的入射光進入元件吸收。 真實的太陽光會隨著時間的不同而改變照射的角度，在實際應用時，太陽能電池如果具有大角度光線入射皆有良好吸收的特性將會是非常重要的，即使在15度到85度廣角度入射光，奈米梯形截頭圓錐週期性結構仍提供了優異的抗反射和光捕捉效果，增加元件整體的光吸收，有效改善光電流密度。利用奈米結構，具有寬頻譜以及廣角度的抗反射能力，增加材料吸收效率，使得元件更適合薄的材料、較便宜的製造成本。

In view of the advantages of low temperature process and high efficiency possibility, the amorphous silicon (a-Si) / crystalline silicon (c-Si) hetero-junction (HJ) solar cells have been studied. Using nano-patterned structure, reducing light reflection to enhance light absorption and increase the short-circuit current density for HIT solar cell. In this paper, design simulation model of nano conical frustum arrays for HIT solar cell surface. The optical properties of the nano conical frustum arrays are theoretically studied via simulation based on the rigorous coupled wave analysis (RCWA) in detail. Hexagonal nano conical frustum arrays is more coverage density than square nano conical frustum arrays due to achieve maximum utilization of space. The results show that the hexagonal nano conical frustum arrays has efficient light harvesting when the ratio of diameter to periodicity (D/P) is around 0.5. The optimal hexagonal nano conical frustum arrays has 400nm of the periodicity(P), 175nm of the diameter(D), 125nm of the height(H) and 750 of the slant angle (θ), yielding an ultimate short-circuit current density of 36.85 mA/cm2, which improve 14.6% than planar HIT solar cells. The angle of incidence of the sun changes during a day and sunlight reaching the earth is a mixture of direct and scattered radiation after passing through the atmosphere. The array of nanostructure can significantly suppress the reflectance to increases short-circuit current density. Excellent broadband and omnidirectional anti-reflection coatings to allow to be reduce the thickness of the substrate and potential to further improve cost-performance.