製作氮化矽次波長結構應用於太陽電池之抗反射層

Abstract

在太陽能電池的應用上，氮化矽薄膜為一常用的抗反射層及鈍化層材料，但其只在特定頻寬內有較佳抗反射效果。因此我們發展一種簡單的製程，在氮化矽上製作次波長結構，期望能達到寬頻抗反射的效果，以增加太陽能電池對光的吸收。首先我們利用旋轉塗佈法，藉由改變轉速、時間及溶液濃度，在氮化矽上製備一單層且整齊排列之二氧化矽及聚苯乙烯奈米球，並以此為遮罩進行乾式及濕式蝕刻。在乾式蝕刻方面，我們利用CF4/O2電漿對氮化矽進行蝕刻，以二氧化矽奈米球為遮罩所得到的結構為一拋物面圓柱，利用聚苯乙烯奈米球為蝕刻遮罩則可得到尖錐狀結構。其中最佳的次波長抗反射結構為利用二氧化矽奈米球為遮罩進行蝕刻，其結構高度為165 nm、底部SiNX厚度為90 nm，並使得波長300~1000 nm的入射光之有效反射率下降到5.45%，達到寬頻抗反射的效果。另外，在濕式蝕刻部分，由於蝕刻遮罩與基材之間的附著力仍然有待克服，因此蝕刻效果不佳。

Silicon nitride (SiNx) is a well-known single-layered antireflective and passive material for solar cells. Unfortunately, the single-layered antireflective coating (SLARC) generally works well within a limited spectral bandwidth. In this research, we develope a simple and low-cost method to fabricate subwavelength structure (SWS) on the SiNx to achieve a broadband antireflection with the objective of increasing the absorption of incident light for solar cells. First, a spin-coating process is carried out with adjustable spin rates, spin time, and concentrations of the dispersion containing SiO2 or PS particles. Subsequently, a single-layer microspherical array on the SiNx is formed. Next, the single-layer microspherical array is employed as the mask for following dry etching and wet etching. For dry etching, we use reactive ion etching (RIE) to etch SiNx and the reactive gas is a mixture of CF4 and O2. Depending on the mask material, a structure of pillar with parabolic surface is fabricated with the SiO2 nanosphere array; a cone structure is observed with the PS nanosphere array. The SiNx SWS with the height of 165 nm and the unetched SiNx thickness of 90 nm reveals excellent antireflective performance with the effective reflectance of 5.45% throughout the spectral range from 300 to 1000 nm. However, for wet etching, due to an unexpected poor adhesion between the substrate and mask, the desirable structure feature is not formed successfully.