室溫下控制一維奈米線陣列結合疏水表面與抗反射之應用

Abstract

成長一維矽奈米線已被透過許多方法來實現，最近更應用在許多元件上，例如：抗反射和具有自我清潔能力。而在太陽能元件的設計上，主要著重在減少表面的反射和增強疏水的特性，我們則是利用表面的改變以及密度的改變來控制這些特性，這些在過去的文獻上並沒有討論這之間的關係。 我們在室溫下透過HF/AgNO3的混和溶液成長一維單晶的奈米線陣列，首先我們可以改變蝕刻時間藉以控制奈米線的長度和密度，我們可以得到線性的成長速率。然後我們透過等效介質理論來計算不同的填充密度的等效折射率，以及利用濕蝕刻的成長機制發展出具有梯度變化的折射率的奈米線陣列，在反射率的表現上具有寬頻譜的良好的抗反射特性平均在1~2%，除此之外與角度相關的反射率也顯示出TE和TM的偏極化光在小入射角(8°)到大入射角(80°)也都具有很不錯的抗反射特性。除此之外我們藉由液滴以及基材的接觸角量測實驗，透過Cassie’s 理論得到不同的填充密度會具有不同的接觸角，同時也具有很好的疏水特性。如果能利用具有抗反射以及表面清潔能力的結構來做元件是一個非常能被期待的發展重點之一。

Various methods to synthesize Si nanowire arrays (Si NWAs) have been developed. Very recently, Si NWAs have been widely utilized for the device applications, such as antireflection (AR) or self-cleaning. The reduction of surface reflection and the super-hydrophobic effect are desirable to apply for solar cells. To the best of our knowledge, there are no reports on the AR and super-hydrophobic effect on the structural properties, such as morphology and density of Si NWAs. In this work, the galvanic wet etching was adopted to fabricate disordered single-crystalline Si NWAs at room temperature in HF/AgNO3 solution. The length and density of Si NWAs could be controlled by adjusting the etching time, and the growth rate is estimated to be linear behavior. An average total reflectance 1~2% over a wide range of wavelength showed the broadband AR characteristics of Si NWAs. Angular dependent of spectral measurements of the Si NWAs are insensitive to TE and TM polarization, demonstrating omnidirectional AR characteristics. Excellent AR behavior is due to the gradient refractive index profile of Si NWAs. The effective index of Si NWAs was calculated by the effective medium theory. Morphology-dependent Brewster angle was observed. Moreover, the self-cleaning effect was examined by the basic contact angle and hysteresis theories. According to the Cassie’s theory, the calculation results agree well with the measured data, showing super-hydrophobic effect. Building self-cleaning feature into a broadband and omnidirectional AR coating can keep contamination to a minimum so that long-term performance of optoelectronic device can be maintained.