利用週期奈米陣列提升矽基太陽能電池光吸收率之應用

Optical Absorption Enhancement in Silicon Nanostructure Arrays for Photovoltaic Applications

蕭伯翰(Po-Han Hsiao)

指導教授 ： 陳聯文

國立成功大學/工學院/機械工程學系碩博士班/碩士(2010年)

摘要

將週期微奈米陣列吸收層應用於矽基薄膜太陽能電池有機會大幅改善其光吸收不佳的特性，本論文主要以有限元素法對週期奈米線及奈米洞陣列兩種結構進行光吸收性的模擬計算與探討。在固定厚度下，針對晶格排列方式、晶格常數、柱體填充比以及截面形狀等各項參數進行對照與比較，並以理論最大效率作一量化。計算後將發現不論變化何種參數，奈米洞陣列都將展現較奈米線陣列具有更佳之光吸收改善。
之後以最佳結果之參數，進一步研究若在奈米洞陣列底部預留一厚度對光陷阱效應的影響。模擬將發現底部預留厚度將較完全蝕刻到底的結構具更進一步的光吸收改善。若以總厚度2.33 μm無預留厚度的奈米洞陣列為基準，將發現僅需總厚度1.5 μm、預留厚度600nm便可具有較此基準更高的最大理論效率。選擇此參數之結構並進一步加入抗反射層及金屬背反射層，用以設計一更薄的太陽能電池，計算結果顯示此設計具有較相同厚度之矽薄膜225%的理論最大效率增益，且相當接近等效體積吸收層以幾何光學設計所能達到的Yablonovitch光陷阱極限，並且在相當寬的入射角範圍內(本文僅分析橫向電場模態( TE-mode )入射) 仍維持相當高的光吸收改善。

關鍵字

光陷阱 ； 奈米微結構 ； 矽奈米線 ； 矽奈米洞 ； 太陽能電池 ； 光子晶體平板

並列摘要

In this study, the optical absorption characteristics of silicon nanostructure arrays, including nanowire and nanohole structures, which have potential applications in thin-film solar cells, are investigated via a finite element method. The fixed overall thickness is considered, in which the effects of lattice arrangement, lattice constant, filling ratio, and the cross-section shape of pillars are simulated and quantified in terms of ultimate efficiency. No matter which parameter, it is found that silicon nanohole arrays exhibit much better absorption improvement than silicon nanowire arrays do.
Moreover, we also numerically study the light-trapping effect as the preserved thickness existing in the bottom of the optimum parameters. We find better absorption enhancement than with the full-etched arrays. When choosing an overall thickness of 2.33 μm for the full-etched nanohole arrays as the reference, it is observed that the active layer possessing the higher ultimate efficiency only needs an overall thickness of 1.5 μm and a preserved thickness of 600 nm. We select these parameters to design a thinner active layer and add the anti-reflection coating and the back metal reflector to it. The results show it has a 225% higher ultimate efficiency than a Si thin film of equal thickness and is very close to the Yablonovitch light trapping limit for the same volume of active material. The optical enhancement effect can be maintained over a large range of incident angles (only analysis transverse electric modes incidence).

並列關鍵字

light trapping ； nanostructure ； silicon nanowire ； silicon nanohole ； solar cell ； photonic crystal slab

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