仿生寬頻奈米結構抗反射層及其在單晶矽太陽能電池之應用

Abstract

週期性奈米結構被廣泛發現於自然界中，像是在蛾眼(moth eye)結構中， 因為這樣的奈米結構可降低光進入眼睛的反射，藉此增加在黑暗中的視覺靈敏 度。一週期小於入射光波長的奈米結構陣列又被稱為次波長結構，可形成具有 漸變性折射係數之結構，藉由改變次波長結構的表面形貌，折射係數會由基材 漸變為空氣。由於這樣的漸變性折射係數，可有效降低因折射係數差異造成的 表面反射，而做為一抗反射結構(antireflection coating)。相對於傳統單層 或多層抗反射薄膜，週期性奈米結構藉由提供一個漸變性折射係數更能有效的 廣域波長範圍達到抗反射效果，此外，此結構擁有對入射角度不敏感的特性， 更能應用於在設計寬廣入射角的抗反射用途，被視為可有效應用於光學元件及 太陽能電池的抗反射結構。 本計畫分為三個部分：(一)單層二氧化矽奈米粒子結構(二) 蜂巢式次波 長結構，以及(三)蛾眼奈米結構陣列。藉由不同的低成本製程方式在太陽能電 池表面形成週期性奈米結構做為提升抗反射以及光捕捉效果，藉此提升太陽能 電池的光電轉換效率。所有的實驗並會以Rsoft CAD Layout DiffractMOD 軟 體進行理論模擬計算設計最佳參數條件以及驗證實驗結果。

Periodic nanostructures, which are found in insects, like moth and some butterflies, provide inspiration for scientists to define both morphology and dimensions, and produce the desired functionality for many important applications. The biomimetic structures, which have been used for AR purposes, provide valuable clues to gradient refractive index fabrication and design for efficient AR structures. Biomimetic AR structure with surface relief gratings may be understood in terms of a thin film, in which the refractive index changes gradually and continuously from the top of the structure to the bulk materials. The period of the so-called sub-wavelength structures (SWSs) is sufficiently smaller than the wavelength of incident light, so that the structures cannot be resolved by the incident light. The direction of the first diffracted order is over the horizon. The SWS can dramatically suppress the reflection and increase light transmission simultaneously at the interface, over a wide range of angles and wavelengths, because the surfaces have many tunable factors, such as period, depth, and cross-sectional geometry. In addition to their high-performance optical properties, SWS arrays exhibit self-cleaning capability because of the high fraction of air trapped in the trough area between arrays. This project, includes three parts (1) monolayer silica nanoparticles structure (2) honeycomb SWS structures (3) moth eyes nanostructure arrays, will fabricate periodic nanostructures on the surface of solar cell devices for antireflection and light trapping. The nanostructures will enhance power conversion efficiency of solar cells by reduce the reflectance. All processes are simple, low cost, and cause no damages on solar cells and will be modeled by Rsoft CAD Layout DiffractMOD.