奈米暗黑半導體的光捕捉

Abstract

捕獲光線對太陽能電池的效能非常重要，因此關於次波長奈米結構的開發，以避免表面反射造成的損失，近來頗受矚目，其中，製造極暗黑的奈米結構材料，是最近相關研究的重點之一。雖然某些材料已被證實具由接近完全不反射與完全吸收的光學特性，但若能製作以半導體材料為基礎的暗黑材料，對太陽能的研究開發更為重要。除此之外，半導體材料也具有與現有太陽能元件製程相容的優點，因而本論文的動機在於提出多種暗黑的半導體奈米結構與材料。論文中我們先介紹氫電漿奈米製造技術應用於各種半導體與介電材料的潛力，並於研究結果的第一部分，以氫電漿在1 μm 厚的多晶矽與非晶矽薄膜上製作出奈米結構，揭露了一種特別的奈米草/奈米截頭錐體雙層結構，具有近乎超暗的光學特性。在論文的第二部分，我們將氫電漿製程拓展至非矽基材料，製作出GaAs的奈米草結構，結果顯示其低反射在不同的波長與不同入射角的條件下幾乎與光的偏振無關。在論文的最後一部份，我們以化學蝕刻法製作了極薄、可撓的單晶矽，並成功地以氫電漿製作奈米草於其表面，根據在300-800 nm極佳的光學吸收與極低的反射結果，顯示此超薄的單晶矽薄片也具有超暗的特性。

Light trapping is very essential for solar cells to enable its efficient performance. Developing sub-wavelength nanostructures to efficiently absorb the light is an attractive method to avoid large reflection losses from any semiconductor material. Fabrication of nanostructured materials with super blackness is one of the cornerstones of present photovoltaic research. Although few super black materials have been proven with near zero reflection and near unity absorption, semiconductor based black materials has become an increasingly important black material for solar cell applications. Furthermore, semiconductor based black materials can be fabricated along with current solar cells technology. In this thesis we explore the fabrication and light trapping properties of nanostructured black semiconductors. The overview of potentiality of our hydrogen plasma etching process to fabricate wide variety of nanostructures including semiconductors and dielectrics is presented. In the first part, we fabricate randomly textured poly-Si and a-Si nanostructures from pre-deposited one micron thin films. We show the unique double layered nanostructures of a-Si nanograss on top of Si nanofrustum behaves as most similar to a black material. In the second part, we demonstrate that the hydrogen plasma etching process can be extended to fabricate grass like GaAs nanostructures. Antireflection performance of almost independent of polarization of the incident light over a broad range of wavelengths and wide range of incidence angle from GaAs nanograss is revealed. In the final part, we explore the fabrication of flexible ultrathin crystalline silicon films by wet chemical etching. We also extended the fabrication of nanograss-like structures on flexible ultrathin crystalline silicon films, using hydrogen plasma etching process. The combination of high optical absorption and extremely low reflectance of the nanostructured ultrathin crystalline silicon films over a broad range of wavelengths from 300 to 800 nm demonstrates its super blackness.