Majlesi Journal of Mechatronic Systems Vol. 10, No. 2, June 2021 39 Paper type: Research paper DOI: https://doi.org/10.52547/mjms.10.2.39 How to cite this paper: M. Gatabi, K. Fasihi, A. Faraji Naghibi and H. Garoosi, “Optimal Design of Silicon Solar Cells using Double Grating Structure”, Majlesi Journal of Mechatronic Systems, Vol. 10, No. 2, pp. 39-45, 2021. Optimal Design of Silicon Solar Cells using Double Grating Structure Mehdi Gatabi 1 , Kiazand Fasihi 2 , Ahad Faraji Naghibi 3 , Hamed Garoosi 4* 1- Mazandaran Regional Electrical Company, Sari, Iran. Email: mgatabi@mazrec.co.ir 2- Department of Electrical Engineering, Golestan University, Gorgan,Iran. Emai: k.fasihi@gu.ac.ir 3- Mazandaran Regional Electrical Company, Sari, Iran. Email: afaraji@mazrec.co.ir 4- Department of Electrical and Computer Engineering, Noshirvani University of Technology, Babol, Iran. Emai: Garoosi.hamed@gmail.com (Corresponding author) Received: February 2021 Revised: April 2021 Accepted: May 2021 ABSTRACT: In this paper, we focus on the refraction of light using gratings (in the front and back areas) in a silicon solar cell as one- dimensional crystal photonics and present the optimal structure for such cells. The front grating is provided with an anti- reflective coating on the absorbent layer (c-Si) to increase the absorption at short and medium wavelengths. We also proposed a back grating (corresponding to the front grating period) on a TCO or metal layer to increase long- wavelength absorption in a full solar cell. Based on this, the optical characteristics and short circuit current have been investigated. The Finite-Difference Time-Domain (FDTD) method is used to optimize the grating parameters for maximum adsorption in the layer (c-Si). Also, optical simulation is performed based on a silicon layer with a thickness of up to 2 micrometers using front and back grating. It can be seen that the proposed structure has about a 40.73% increase in current density compared to the case where only the anti-reflective coating used with the smaller active area is used and about 15 to 38% increase in current density compared to the cases where the front grating is used. Therefore, the proposed structure with a smaller active region thickness has a higher current density. KEYWORDS: Solar Sell, Photonic Crystal, Grating, FDTD, Refraction. 1. INTRODUCTION INCREASING absorption through photonic crystals has been recommended as a promising approach to improve the optical performance of solar cells, aiming at usage made of one-dimensional, two- dimensional, and three-dimensional periodic structures covering a wide range of light diffraction. In fact, a photonic crystal is a structure with a lattice constant of wavelength order whose refractive index changes periodically [1], [2]. If the change would be taken place in one direction of the space, it would be called a one-dimensional photonic crystal; however, if the change takes place in two or three directions of the space, it will be called a two-dimensional or three- dimensional photonic crystal[3], [4]. Recently, using photonic crystal as a back reflector or effective antireflection coating (AC) has been recommended to increase absorption inactive region [5, 6].The concept of producing more effective absorption has been recommended by Meng et al. and their design included one layer of hydrogenated amorphous silicon as a flat photonic crystal to couple radiated lights in Bloch standing modes on the light path to control photon life cycle. This was designed based on the concept of (a-Si:H) solar cells along with photonic crystal[7], [8].Similar approaches have been studied for organic solar cells, showing higher absorption [9].Another design is using diffraction grating in thin- film solar cells. In fact, diffraction grating provides many capabilities to cells. Also, they can be used as advanced back reflectors to increase the path length and spectral density of optical modes in long wavelengths or as a front anti-reflection coating to reduce total reflection and to increase transmitted light; or, as recently recommended they can be used as a combined reflector and front anti-reflection coating in one cell via a pattern of different layers [6], [9].A diffraction grating is an optical component with a periodic structure dispersing the light in different directions[10]. The direction of these lights is