Copyright © 2011 by ASME 1 ASME International Mechanical Engineering Congress & Exposition IMECE November 11-17, 2011, Denver and the Colorado Convention Center, USA IMECE 2011: 62352 Numerical Simulation of Thin-Film Photovoltaic Solar Cells Khairy Sayed Sohag University Sohag, Egypt Mazen Abdel-Salam Assiut University Assiut, Egypt Mahmoud Ahmed Assiut University Assiut, Egypt Adel A. Ahmed Assiut University Assiut, Egypt ABSTRACT The objective of this work is to develop a detailed numerical simulation of solar photovoltaic cells in one, two, and three-dimensions. Such kind of numerical simulation can be used as a flexible research tool for the design and analysis of solar cells. The developed in-house simulation code has the advantage of conducting modifications of the suggested configurations to include effects not covered by the commercial simulation models. In addition, this tool is to serve as a test-bed simulator for the development of solar cells modeling and to design new material models. The photovoltaic solar cells governing equations are Poisson's equation, the hole and electron continuity equations. Poisson equation is generally used to get the voltages across the device. However, in the present work, it is used to obtain the value of the electrical charge. The governing equations along with the appropriate boundary conditions are solved numerically using a finite difference based method. The resulting system of coupled nonlinear equations is then solved using Newton method for nonlinear systems. The predicted results include illuminated current-voltage characteristic, and dark current-voltage characteristics of photovoltaic module. Comparisons between predicted results and corresponding measured values by manufacturer are conducted in order to validate the numerical simulation. A good agreement between predicted and measured results was prevailed. I- INTRODUCTION High efficiency solar cells with 2-dimensional geometries are governed by non-linear effects and require powerful simulators for their study. Numerical modeling is increasingly used to obtain insight in to the details of the physical operation of thin-film solar cells. Over the years several modeling tools specific to thin-film PV devices have been developed. A number of these tools have reached a mature status and are available to the PV community like SCAPS, PC1D, BIDIM2, AMPS [1-5]. Thin-film solar cell devices are modeled in two dimensions, from fundamental material parameters, using the finite element method [6]. The electrostatic potential is solved for, together with the quasi-Fermi levels, while optical absorption is calculated from n and k values of the materials used. Fundamental semiconductor equations (Poisson's equation and continuity equations) are solved [6] in 2D for thin-film solar cells, using the finite element method. Two examples of applications on Cu (In; Ga) Se2 based thin-film solar cells with absorber material in homogeneities have been presented [6]. In the first example the band gap energy is randomized, while in the second one the mid-gap trap state density is varied. In this paper, a software program specially oriented to the numerical analysis of solar cells is presented. It has been developed in MATLAB, and uses the finite differences method with a new iterative scheme for numerical resolution of semiconductor equations. A combination of convenient user interface, rapid convergence, and the ability to address complex issues associated with heavy doping make this program is convenient for solar cell research. A simple expression for the effective electric field is derived, which allows one to more clearly study its variation with the injection level, and to easily take into account the electric field-dependence of the mobility II. SYSTEM DESCRIPTION The basic equations describe the behavior of charge carriers in semiconductors under the influence of an electric field and/or light; both cause deviations from thermal equilibrium conditions. In the following they are simplified to one dimension particular to the p-n junction. A. Poisson’s equation The Poisson's equation correlates the gradient of the electric field E with the space charge density ρ. In one dimension it is given by Proceedings of the ASME 2011 International Mechanical Engineering Congress & Exposition IMECE2011 November 11-17, 2011, Denver, Colorado, USA IMECE2011-62352