利用二維陣列自組裝奈米小球提升太陽能電池之效率

Abstract

有效降低光在表面的反射率是提升太陽能電池效率的一個重要的課題，許多研究針對整體電池結構上的改變來尋求反射率的降低進而使入射的光子變多。 在本篇論文中，我們發現到具有奈米結構的光二極體有較低的載子傳輸時間以及較低的反射率，其中奈米結構是透過奈米小球微影術所製成。 接著我們將二氧化矽奈米小球旋轉塗佈在太陽能電池的表面上，因此電池的整體結構並不會改變。這是一個較為實際且有機會導入業界的方法。此二維的奈米小球陣列將會提升包括垂直入射時以及斜向入射時的太陽能電池轉換效率。這個改善是由於此二維陣列產生了利於光子傳導的模態，使得入射光子導入吸收層的數量增加，意即有效的減少了光反射率。 我們也發現到此二維陣列對於電場垂直極化的光有較大的提升而對磁場垂直極化的光幫助則較少，正好可以彌補電場垂直極化的光在光學上反射率較高的問題。若奈米小球可被塗佈於更大面積，則有很大的機會可被導入業界。

For solar cells, it is generally thought that surface reflectivity is one of the bottlenecks that limited the conversion efficiency. Tremendous efforts have been spent on reducing the reflectance using different structures to trap more photons in the solar cells. In this thesis, nanopatterned photodiodes are found to have faster transit time and lower reflectivity. The nanopatterns are made by nanosphere lithography. Silica nanoparticles were then coated on the solar cell surface without altering the whole structure. It’s a more practical method for the industry purpose which would not like the complicated processes involved. The two dimensional nanoparticle arrays improve the efficiency not only at normal incidence but also at oblique incidence. The improvements are attributed to the guided modes excited by the two dimensional silica grating structure and the reduction of the reflectivity. Furthermore, we found the silica nanoparticles improve the TE polarized light more significant than TM polarized light, which is a good way to compensate the larger reflectivity in TE polarized light for oblique incidence. If the nanoparticles can be coated on a large area, it will have a profound effect on solar cells industry.