二氧化鈦仿生抗反射結構於磷化銦鎵/砷化銦鎵/鍺三接面太陽電池

Abstract

我們成功的利用奈米球微影技術(Nanosphere lithography)製作大面積的二氧化鈦之仿生次波長抗反射結構，並且將其應用於三接面三五族太陽電池之上，結構是利用反應式離子蝕刻儀器之非等向性乾蝕刻所製作，調變蝕刻氣體參數即可改變次波長結構之表面形貌，此種抗反射結構比起一般傳統單層抗反射層有著更好的寬頻譜抗反射能力，除了一般傳統抗反射層最優勢的特定波段，此外的範圍都可以有著更低的反射率；我們利用了此種抗反射的特性應用在磷化銦鎵/砷化銦鎵/鍺三接面太陽電池上，相較於沒有抗反射結構與傳統單層抗反射層的太陽電池，分別提升了28.3%與1.7%的光電流。 本篇論文介紹了如何製作二氧化鈦仿生次波長抗反射結構，我們利用旋塗法將奈米級別的聚苯乙烯小球製作出大面積的單層週期性結構，再利用非等向性蝕刻控制結構的形貌，利用其漸變折射率的原理有效的降低了反射率，並且發現此種結構也具有優異的寬頻譜抗反射特性；我們也把此種結構做在太陽電池表面，並且量測其光電轉換效率，外部量子效率以及變角度光電轉換效率，以上的量測都顯示出次波長抗反射結構優於單層抗反射結構。接著我們進一步的改善了蝕刻參數，製作出更接近理想形貌的次波長結構，並且運用RCWA貼近量測反射率，並改變次波長結構之週期與高度等參數，搭配太陽光譜與計算出的反射率以推測最高之效率；此外我們也發現了二氧化鈦此種材料會損害太陽電池表面，造成電池本身電性稍微降低，不過此並不會影響太多整體效率。

We have successfully fabricated large-scale TiO2 biomimetic sub-wavelength structures (SWSs) by using polystyrene nanosphere lithography and applied to triple junction III-V solar cells. The structure is fabricated by reactive ion etching, which allows the control of sidewall profile by tuning the etching gas ratio. The SWS exhibit better broadband antireflective properties than a conventional single-layer antireflective coating (SL-ARC). Compared to the SL-ARC which shows extremely low reflection in a certain wavelength range, the SWSs show a broadband spectral response of anti-reflection characteristics. We further fabricated the SWS on an InGaP/InGaAs/Ge triple junction solar cell. The photoncurrent was enhanced by 28.3% and 1.7%, compared to the cells without an ARC and with a SL-ARC, respectively. In this thesis, we first optimized the SL-ARC for a triple-junction solar cell by changing the thickness of TiO2 from 40nm to 100nm, and calculated the current density with AM1.5g spectrum to find the highest one. Next we fabricated a cell with SWSs for antireflection and also measured the reflection at different angles of incidence (AOI). The cell with SWSs revealed excellent broadband and omni-directional antireflective properties. Consequently, both the photocurrent and power conversion efficiency were enhanced due to increased optical absorption. We further employed a rigorous couple wave analysis (RCWA) method for optical modeling and reflection engineering by changing the dimensions of SWSs to obtain a maximum output current density. It is also observed that an ideal close-packed SWS exhibits extremely low surface reflection, showing its great potential as an antireflective layer for concentrator photovoltaics.