黑色矽巨孔洞陣列結構應用於矽晶太陽能電池之研究

Abstract

隨著石化燃料日益短缺與環保意識的高漲，人類亟需一種乾淨、無污染的能量來源，以應用於再生能源。太陽光能取之不盡，用之不竭，在發電的過程中無噪音且零汙染，因此，太陽能電池被視為最具潛力的再生能源。目前市面上的商用太陽能電池，其抗反射結構僅侷限於隨機金字塔結構，並無法達到最佳的抗反射效能。有鑑於傳統的太陽能電池製作方法，對於抗反射效能的提升極為有限，故本研究提出以黃光微影定義圖案搭配光輔助電化學蝕刻(PAECE)之整合技術，在矽晶片表面製作高深寬比的黑色矽巨孔洞陣列結構，而此結構將使太陽電池具有較佳的抗反射效能。

多孔矽成長於525 um與380 um之矽基板，當PAECE蝕刻時間為0.5 hr、1 hr、1.5 hr及2 hr條件下，皆能得到黑色矽巨孔洞陣列結構，且其反射率皆能大幅度降低。在280 nm-800 nm波長範圍內，空白矽晶片的平均反射率為37.35 %。未經過PAECE蝕刻的倒金字塔陣列，平均反射效率為6.2 %；具倒金字塔陣列再經PAECE蝕刻後，於525 um之矽基板條件下，經過30分鐘的PAECE蝕刻後，平均反射效率可大幅降低為1.02 %，而經過2 hr的PAECE蝕刻後，平均反射率更可降低為0.81 %。若晶片減薄至380 um時，經過2 hr的PAECE蝕刻後，能進一步降低反射率至0.72 %。此時結構除了具有倒金字塔的形貌外，尚還具有深凹的巨孔洞、微溝渠、隨機多孔矽及黑色多孔矽薄膜層等五種特殊結構。本研究提出的新型複合結構將能具有良好的光捕捉效應，並且增大受光表面積與P-N接面面積，可實際應用於單晶矽太陽能電池，將使太陽能電池的效率能進一步提升。With the fossil fuels are shortage day by day and the raised environmental consciousness, humans need anxiously power sources which are clean and environmental friendly and applicable to on renewable energy. Solar energy is inexhaustible, calm and environmental friendly in the power generation. Therefore, solar cell is thought as the most promising renewable energy. Nowadays, commercial cell usually use the random pyramid as an antireflective structure, but its antireflective performance is not very well. The improvement of antireflective performance for conventional solar cell is not easy to achieve. Therefore, this study presents the integration of photolithography and photo-assisted electrochemical etching (PAECE) to fabricate a black silicon macroporous arrays with a high aspect ratio on the surface of silicon wafer, it will improve antireflective performance significantly.

Porous silicon (PS) was grown on the 525 um and 380 um thick silicon wafers. The black silicon are produced after PAECE under the etching time of 0.5 hr, 1 hr, 1.5 hr, and 2 hr, respectively. The macroporous arrays with low reflection in the 280-800 nm wavelength regimes can be easily achieved. The weighted mean reflectance of a blank silicon wafer is 37.35 % in the 280-800 nm wavelength regimes. Inverted pyramid arrays without PAECE can reduce the weighted mean reflectance to 6.2 %. Inverted pyramid arrays with 30 min PAECE reduce the weighted mean reflectance even to 1.05 % on the 525 um thick silicon wafer. Besides, after PAECE of 2 hrs can reduce the weighted mean reflectance to 0.81 %. Besides, if the thickness of silicon wafer is decreased to 380 um, the weighted meanreflectance after PAECE of 2 hrs process further reduce to 0.72 %. The novel structure of combining inverted pyramid, deep macroporous, micro-trench, random porous, and black porous membrane can be observed simultaneously. Such a compound antireflective structure proposed in this study has the advantage to enhance light trapping, increase the area of light absorption and P-N junction, and can be applied as an antireflective structure to single crystalline silicon solar cell to improve its performance of efficiency.