奈米結構單晶矽太陽能電池之製程及研究

Abstract

本篇論文主要研究單晶矽太陽能電池表面上奈米結構的抗反射層的製程及其對其太陽能電池轉換效率的影響。 本論文中我們使用三種不同的蝕刻方式來製作奈米結構。第一種方法是目前業界常用的濕蝕刻方式，利用KOH溶液在表面上形成許多微小的金字塔結構。第二種方法是在矽晶圓上濺鍍一層薄薄的銀層，經過高溫爐退火後，形成一顆顆銀顆粒，這些銀顆粒可當作蝕刻遮罩，最後對附有銀顆粒的矽晶圓進行反應式離子蝕刻，便可在晶圓表面形成奈米柱。第三種方法是利用電子迴旋共振電漿反應器來製作奈米尖錐結構，首先在矽晶圓上形成SiC作為蝕刻遮罩，緊接著以Ar及H2對附有SiC的矽基板進行乾蝕刻，如此便可得到奈米尖錐。 樣品完成後，我們以傅利業紅外線光譜分析儀量測奈米結構在可見光與近紅外光波段的反射率，我們發現奈米柱及奈米尖錐結構具有較為寬廣的低反射率波段。最後我們利用高溫擴散法在長有奈米結構上的p-type矽基板上形成PN接面，製成太陽能電池，我們發現奈米柱結構具有最佳的轉換效率，效率可較前業界常用的濕蝕刻方式提升82%，而奈米尖錐結構具有極佳的抗反射效果，但由於結構容易受到破壞且表面缺陷多，造成轉換效率反而變低。

In this thesis, different methods of fabricating nanostructures on the surface of single crystal silicon for antireflection were investigated and the influences of these nanostructures on the conversion efficiency of the solar cell were studied. Three methods were used to make nanostructures. The first method was wet etching method which has been wildly used in the solar cell industry. KOH solution was used to wet etch Si surface and many small pyramidal structures were formed after the wet etching. The second method was using reactive ion etching with Ag nanoclusters as etch mask. In this method, a thin Ag film was deposited on the silicon surface first, then the sample was thermally annealed to let Ag film dewet into Ag clusters and serves us etch mask. After reactive ion etching, Si-nanopillars were formed on the Si surface. The third method was using the electron cyclotron resonance (ECR) to make the nanotips structure. The SiC clusters which were formed on the Si substrate in the beginning of ECR process could be used for etch-mask. After the unmasked region is etched by Ar and H2, Si-nanotips were formed on the surface. Fourier transform spectrometer was used to measure the reflection of the surface with nanostructures in the VIS and NIR regions. The samples with nanopillar and nanotip structures were both found to have lower reflection in these spectral regions than the sample made by using wet etching. Solar cells were then made by using thermal diffusion of n-type dopants into the samples, and we found that the solar cells with the nanopillar structures had the best conversion efficiency. The efficiency is enhanced by 82% over the solar cell made with conventional method. On the other hand, although the sample with nanotip structure has excellent antireflection property, after making into solar cell it has very poor efficiency. This is because the nanotip structures were destroyed in the high temperature process in making the solar cell.