單晶矽晶片倒金字塔製絨製程之研究

Abstract

Texturing is a crucial step for solar cells, especially for monocrystalline silicon to capture more sun light for higher conversion efficiency. A few surface structures could be generated from the texturization of silicon wafer. Among them, the pyramid structure is the most popular one for (100) monocrystalline silicon wafer due to its robustness by using alkaline solution. Because of the longer texturing time is needed, the batch processing is normally used. On the other hand, the inverted pyramid (IP) structures could achieve a better light trapping, but the processing window is narrow. So far, it has not yet been considered in mass production. In the previous research, the IP texturing based on the alkali/isopropyl alcohol (IPA) at high temperature (75 °C- 85 °C) has been reported, but the texturing time is long up to 20 min. There are also other reports using acid solutions, such as HF/HCl/H2O2 at 25 °C or Cu(NO3)2 / HF / H2O2 / H2O solutions at 50 °C, but the processing time was long as well. Another that, there is a report about the IP texturing based on the TMAH solution at 70 °C for 30 min. In this research, a three-step process was proposed. In the first step, the (100) monocrystalline silicon wafers were pretreated by the metal catalytic texturing (MCT) to generate nanoholes. Then, acid solutions containing hydrofluoric (HF) and nitric (HNO3) acids were considered in the second step and then the third step is etching with anisotropic solution. Anisotropic solutions containing tetramethylammonium hydroxide (TMAH) and some additive. In the pretreatment, the silver particles were deposited first by electroless plating using AgNO3 solution, followed by HF etching to generate nanoholes structure. Si porous surface will modified by isotropic etching in HF and HNO3. In this study, nano inverted pyramid structure (NIPs) were obtained by anisotropic etching in TMAH solution with some additives at 25 °C. The reflectivity of monocrystalline before texturing was around 27 % and after texturing the reflectivity became 9.07 %. This texturing technique has a potential to reduce the use of metal component in industries that can pollute the environment.