矽奈米線陣列結構應用於光伏元件之分析

Abstract

我們成功利用奈米球微影術(Nanosphere lithography, NSL)搭配金屬輔助化學蝕刻法(metal-assisted chemical etching, MACE)製作出大面積矽奈米線陣列結構，並從反射率量測中證實矽奈米線陣列結構具有寬頻譜(broadband)以及廣角度(omnidirectional)的抗反射能力，接著我們還使用兩種非接觸式光學量測技術來觀察樣品內總超量載子濃度的衰退情形，分別為Microwave photoconductive decay (u-PCD)以及Resonant-coupled photoconductive decay (RCPCD)，並且進一步分析量測結果求得少數載子的生命期，最後將矽奈米線陣列結構應用於太陽能電池，再利用光電轉換效率以及外部量子效率量測分析，探討矽奈米線陣列結構對元件特性的影響，同時亦利用模擬軟體研究太陽能電池在不同PN接面輪廓下，擴散長度對元件光電轉換效率的影響。 本論文的第一部分討論如何製作矽奈米線陣列結構，我們採用旋塗法搭配奈米球微影術這種大面積、便宜又快速的方法，加上非等向性金屬輔助化學蝕刻法達到對矽奈米線陣列結構大小的良好控制，並使用內建有積分球的光譜儀進行反射率量測驗證該結構具有優異的抗反射特性，也從光電導衰退量測結果搭配我們的理論模型分析奈米線長度對少數載子生命期的影響。 在第二部分中，先介紹矽奈米線陣列結構製作成太陽能電池的步驟，並自元件表面的反射率、光電轉換效率以及外部量子效應等量測結果對元件特性進行分析，最後利用電性模擬軟體分析傳統平的PN接面與core-shell的PN接面太陽能電池，結果顯示core-shell的PN接面太陽能電池在擴散長度變短時其短路電流密度與光電轉換效率下降較少。

We have successfully fabricated large-area silicon nanowire (SiNW) array structures by employing the polystyrene nanosphere lithography and the metal-assisted chemical etching (MACE). Compare to the conventional single layer anti-reflection coating (SLARC), SiNW array structures show broadband and omnidirectional antireflection properties in the reflection measurements. Afterward, we used two kinds of optical techniques based on photoconductive decay (PCD) to provide a contactless measurement for determining the minority carrier lifetime of SiNW arrays. SiNW array structures were made into solar cells, and we analyzed the impact of SiNW array structures on the device characteristics through both the power conversion efficiency and external quantum efficiency measurements. Furthermore, the influence of the minority carrier lifetime on the power conversion efficiency was analyzed under two different PN junction profiles by simulation. In the first section, we discuss how to fabricate SiNW array structures. An optimized spin coating method was employed for the large-area deposition of polystyrene nanospheres, followed by the anisotropic MACE to form SiNW arrays. We could observe broadband and omnidirectional antireflection properties on SiNW array structure by the spectrophotometer system with a built-in integrating sphere. A theoretical model was proposed to calculate the minority carrier lifetime by fitting the experimental PCD curve, and then the influence of the length of SiNWs on the minority carrier lifetime was obtained. In the second section, we made SiNW array structures into solar cells and the SiNW array solar cells were characterized under the AM 1.5G illumination condition and analyzed by external quantum efficiency measurement. Besides, we compared the device performance between traditional planar PN junction solar cell and the core-shell PN junction solar cell by simulation. The simulation results show that shorter diffusion length of the core-shell PN junction solar cell doesn’t seriously decrease short-circuit current density and power conversion efficiency compared to the conventional one.