International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395 -0056 Volume: 03 Issue: 12 | Dec -2016 www.irjet.net p-ISSN: 2395-0072 © 2016, IRJET | Impact Factor value: 4.45 | ISO 9001:2008 Certified Journal | Page 478 Experimental Study of Electrochemically Prepared Porous Silicon as Antireflective Material in Solar Cells P. Sunil Kumar 1 , R. S. Dubey 1 1 Advanced Research Laboratory for Nonmaterials and Devices, Dept. of Nanotechnology, Swarnandhra College of Engineering and Technology, Seetharampuram, Narsapur (A.P.), India ---------------------------------------------------------------------***--------------------------------------------------------------------- Abstract - Discovery of Porous silicon has opened a door of research on this material for their wide range of applications such as energy conversion, optoelectronics, microelectronics, bio-technology, micro-optics etc. Porous silicon acts as antireflection coating material therefore; this has been demanded in solar cells to limit the surface reflections. The great advantage of using porous silicon in solar cells is its large surface area and tunability of its properties. In this paper, we present the optical and structural properties of porous silicon using Filmetrics, Fourier Transform Infrared Spectroscopy, UV-VIS reflectance and Field emission scanning electron microscopy. Key Words: Porous Silicon, Antireflection Coating, Porosity, Etching, Reflectance. 1.INTRODUCTION Porous silicon is a semiconductor material composed of silicon structure with network of air voids. A major research on this material was focused after the discovery of quantum confinement effect by Canham in the year 1990 [1].During his experiment, he had observed an emission of light from the silicon wafers during the chemical dissolution. The high surface to volume ratio and tuning of its porosity make this material suitable as an antireflective coating. Crystalline silicon is the primary material used in solar cells which has high refractive index with a significant portion of solar radiation loss from its surface which leads to in-sufficient electron-hole pair generation and therefore, low-efficiency from the solar cell. Converting silicon into porous silicon acts as a promising material to lower the reflectance off the surface by trapping more photons which are used to generate electron-hole pairs. The refractive index of the host silicon materials can be reduced to a desired level as per the application. The refractive index can be tailored with the porosity of porous silicon by varying the applied current density, HF concentration, etching time and current density. The porous silicon is made by the electrochemical etching or anodization of silicon wafer which is an easy and cost-effective method. This method is a top-down method which employs a platinum electrode as cathode and silicon wafer as anode immersed in a HF concentration that acts as an electrolyte with a constant current source to maintain homogeneous porous layer formation. Porous silicon is having good mechanical robustness, compatibility and reliability that is why have got demanded in various applications like chemical sensors, biological sensors, energy conversion devices, optical memory devices, waveguides etc.[2-6]. In this paper, we present the structural and optical properties of anodized porous silicon for its low-reflection application. The experimental procedure to fabricate porous silicon by anodization cell is presented in Section 2 and characterized results are discussed in Section 3. Section 4, concludes the paper. 2. Experimental Procedure For electrochemical anodization, boron doped silicon substrates p-type of (100) orientation were used. Before electrochemical anodization, the silicon substrates were cleaned to remove the dirt and other possible contaminants. The cleaning process involves the rinsing of silicon substrates in de-ionized water after the separate heating in trichloroethylene, acetone and methanol solutions for 10 minutes at 60°C respectively. After cleaning, the substrates were dried in the presence of nitrogen gas and then used for the anodization. The electrochemical etching setup used in this experiment is shown in figure 1.It consists of a constant current source CH1100A (USA) and a teflon cell is composed of platinum as cathode and silicon substrate as anode which is depicted in figure 1(a). The electrolyte solution was made up of 1:1:2 of HF:DI:Ethanol where HF and DI are the hydrofluoric acid(48%)and deionized water respectively. The anodization cell was made of teflon material because it is chemically and thermally stable. During anodization, when only HF is used as an electrolyte then hydrogen bubbles are generated which sticks to the surface and leads to a lateral and in-depth in- homogeneity. To overcome problem, ethanol is added to the hydrofluoric acid which is helpful to eliminate the hydrogen bubbles and yields uniform etching. Two electrode configurations is used for the anodization of silicon substrates as shown in figure 1(b) and the etching was performed at room temperature in the dark. The silicon wafer was placed on ǮOǯ ring to avoid the leakage of electrolyte and to ensure etching on one-side of the silicon substrates.