標題: 奈米圖形化玻璃基板應用於非晶矽薄膜太陽能電池
Patterned glass substrates for enhanced solar energy harvesting in thin film solar cells
作者: 蔡育霖
Tsai, Yu-Lin
郭浩中
Kuo, Hao-Chung
顯示科技研究所
關鍵字: 奈米結構;抗反射;光捕捉;非晶矽;薄膜太陽能電池;nanostructure;anti-reflection;light trapping;thin film solar cell;a-Si
公開日期: 2010
摘要: 本論文中,我們針對矽薄膜太陽能電池主動層厚度不足,導致太陽光能量吸收效率不佳的問題來進行改良,其中特別改善長波長範圍太陽光之吸收效率,並增進矽薄膜太陽能電池之光電轉換效率。 玻璃基板經常被使用作為矽薄膜沉積之基板,我們利用聚苯乙烯微奈米小球自聚集之特性,成功地將聚苯乙烯微奈米小球鋪排在玻璃基板上,並形成單層六方最密堆積的週期性結構,在此研究中我們利用微奈米球微影技術直接將大面積奈米結構製作於玻璃基板上,並可利用乾式非等向性反應式離子蝕刻參數的調整,得到不同形貌的次波長結構,並得到不同的抗反射與散射效果。 本篇論文第一部分討論如何在玻璃基板上製作次波長抗反射結構。首先我們以濕蝕刻製程利用氧化物緩衝蝕刻液來蝕刻玻璃基板,但在實驗中我們發現,以氧化物緩衝蝕刻液來蝕刻玻璃基板時的側向蝕刻速率,遠高於縱向蝕刻率,我們並無法得到深寬比足夠的奈米結構,因此我們認為濕蝕刻並不適合用來製作奈米結構玻璃基板。因此我們轉向利用旋塗法在玻璃基板上製作周期性的單層聚苯乙烯小球周期性排列,此方法成本低廉又快速,更進一步我們成功利用乾式非等向性反應式離子蝕刻技術在玻璃基板上製作出仿生結構。第二部分,我們將此種具有仿生結構之玻璃基板應用於非晶矽薄膜太陽能電池上,並針對元件之反射率、外部量子效應、光電轉換效率等來進行分析,並以變角度反射率量測來證明次波長結構在變角度下仍然有不錯的抗反射效果,因此我們觀察到全波段量子效率的提升,將此具有仿生結構之玻璃基板基板應用於非晶矽薄膜太陽能電池上,相較於使用沒有製作仿生結構之平面玻璃基板太陽能電池元件,提高了51.6%光電流增加與光電轉換效率48.4%的增強,相較於常被用於業界具有微米結構的Asahi-U基板元件,也提升了8%的光電流,與3.1%光電轉換效率,有效驗證了仿生結構玻璃基板對於非晶矽薄膜太陽能電池光電轉換效率之提昇是有幫助的。 其中我們也利用RCWA模擬將仿生結構的周期與高度作最佳化的分析,於實際元件製作中我們發現,受制於非晶矽薄膜之厚度過薄,高度過高的仿生結構將導致薄膜覆蓋不均勻,影響元件電性之表現,因此光學最佳化之結構並不一定能得到最佳的光電轉換效率,在太陽能電池元件電性與仿生結構高寬比的分析中,我們認為在考慮電特性的情況下,最佳的玻璃基板奈米結構深寬比大約界於0.2~0.3之間,這樣的深寬比選擇讓我們在光學特性與電特性中找到平衡,雖然我們最後所採用之結構並非光學最佳化之結構,但我們仍然觀察到使用仿生結構玻璃基板的非晶矽薄膜太陽能電池有全波段的外部量子效率提升,與光電轉換效率的提升。 最後我們相信如果我們能解決因過大的奈米結構深寬比,而導致薄膜覆蓋不均勻並導致元件電性下降的問題,仿生結構玻璃基板必定能提升更多的太陽能電池轉換效率。
The amorphous silicon (a-Si) thin film solar cell was considered for future generation of photovoltaic applications due to the low cost. However, due to the thin active layer (<1um), it shows a low absorption coefficient at near-infrared region. How to improve light harvesting is a very important issue in high efficiency a-Si thin film solar cell. Antireflection and light trapping are key techniques for efficiently harvesting solar photon. Several studies of sub-micrometer gratings (SMG) structure demonstrate the SMG structure offer a graded refraction index interface, and shown ultra-low reflectivity, another feature of SMG structure is diffraction of light, which get longer optical path length and then further enhance the light absorption of a-Si thin film. In this work, the enhanced conversion efficiency is demonstrated in nanostructured glass substrate for a-Si thin film solar cell, and the nanostructured glass substrate was fabricated by using nanosphere lithography and RIE techniques. The measured external quantum efficiency shows a broadband light absorption, which specially enhance the light absorption in near-infrared. The nanostructured substrate provided both antireflective characteristic and light scattering characteristic for improving the solar energy harvesting. From the result of the I-V characteristics, we observe the electrical property will decrease when the H/D ratio of biomimetic structures increase. We believe that higher H/D ratio of biomimetic structure will result in uneven coverage of thin film growth. From the experiment result, we conclude the best H/D ratio for biomimetic glass structure applies in a-Si thin film solar cell is around 0.2~0.3. Finally we demonstrated the biomimetic glass substrate (nipple shape arrays) which is useful in harvesting solar photon and enhancing the power conversion efficiency of a-Si thin film solar cell. Compared with a flat glass substrate cell and Asahi-U glass substrate cell, the power conversion efficiency achieved 48.4% and 3.1% enhancement, and the Jsc achieved 51.6% and 8% enhancement respectively.
URI: http://140.113.39.130/cdrfb3/record/nctu/#GT079815530
http://hdl.handle.net/11536/47251
Appears in Collections:Thesis


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