次波長抗反射結構於光伏元件之應用

Abstract

傳統上，抗反射層的設計大多由單層或多層折射率介於空氣與半導體之間的薄膜材料製成。然而這種製作方式面臨許多的問題，例如需要高度真空的製程環境、膜與膜之間材料的選擇以及薄膜熱膨脹係數及厚度的控制等。蛾眼上的奈米結構具有寬頻譜的抗反射特性，這項發現使類似的次波長仿生結構成為抗反射層的另一個選擇。最近的研究中有許多研究團隊提出不同製作次波長抗反射蛾眼陣列的技術，例如雷射光干涉法、電子束顯影法、奈米壓印等。但是受限於這些技術設備成本太高或無法大面積製作，因此無法有效地降低太陽能電池的成本。在本論文中，我們成功利用了膠體奈米球微影術(Colloidal Nanospheres lithography)製作大面積仿生蛾眼陣列的次波長抗反射層結構應用在多接面三五族太陽能電池、單晶及多晶矽太陽能電池上，並利用乾式非等向性反應式離子蝕刻的參數調整達到形貌控制的效果進而比擬蛾眼結構，比傳統四分之一波長厚度的抗反射層更具有寬頻譜範圍的抗反射能力，除了500nm~700nm為傳統單層抗反射層的優勢之外，都可普遍使反射率大幅降低。由於在紫外光與近紅外光的抗反射特性，應用在不同類型的太陽能電池上，相較於沒有製作抗反射層以及傳統單層抗反射層的太陽能電池元件，皆能有效地提升元件的效率。另外我們也使用嚴格耦合波分析(rigorous coupled wave analysis)模擬軟體進行結構的最佳化，進一步預測在製程可行的範圍內，不同的結構寬度及高度對元件吸收及產生之光電流密度的模擬，可由此得知往後實際實驗的方向，並減少製程上不必要的測試與時間。

Traditionally, the antireflective design is using the single or multi-layer materials. The n is the refractive index of the semiconductor. However, this production method is faced with many problems; such processes require a high vacuum environment, material selection between the layer, thermal expansion coefficient, and thickness control. The moth-eye nanostructure has a wide spectrum of anti-reflective properties. The discovery let the sub-wavelength biomimetic structure become an alternative for antireflective layer. Recently, a number of research teams made different sub-wavelength antireflective moth-eye array by nanotechnologies: such as laser interferometry, electron beam lithography, and nanoimprint. However the high costs of these technologies or not large-scale production result in cannot effectively reduce the cost of photovoltaic. In this thesis, we successful fabricated the large area of subwavelength moth-eye-like antireflective layer by using the colloidal nanospheres lithography, and applied in the III-V triple junction, crystalline silicon, and amorphous silicon photovoltaic devices. The sidewall profiles of sub- wavelength structures were controlled by adjusting anisotropic etching parameters to mimic moth-eye structures. Compare to the conventional single-layer anti-reflective coating (SL ARC) which shows suppressed reflectance in 500 nm~700 nm wavelengths, the SWS ARC shows a broadband spectral response of reflection characteristics. Hence, the conversion efficiency of the different photovoltaic devices can be effective enhanced due to much improved current-matching, compare to traditional antireflective design.We also setup an optimized design of subwavelength by using rigorous coupled wave analysis (RCWA) method, to predict the photocurrent density for different width and height of the subwavelength in the practicable manufacturing process.