Optimal design of solar cell front-contact grid

Abstract

In order to obtain high efficiency solar cells, the front contact metal grid must be optimized to attain the appropriate grid pattern. An optimization procedure based on a distributed network model and Kirchoff's current law forming a system of equations was carried out and solved for a solution of an output current for each boundary voltage. In this work, we focused on a multilayer thin film solar cell based on the structure Cu(In, Ga)Se[subscript 2]/CdS/ZnO/metal-grid. The photo-generated current, which was found to be less than 35 mA/cm[superscript 2], varied as a function of the boundary voltage. A numerical technique was used to find the current-voltage characteristics and the efficiency for an assumed grid pattern. The optimization estimated the relationship between diffusion length and the width of the cell for best cell efficiency. The longer the diffusion length was, the larger the optimal width of the cell could be obtained. However, the optimum was not occured in short diffusion length. Furthermore, the optimization for fork-shaped grid patterns with two parallel arms was performed to achieve grid parameters, e.g. the spacing between the two arms and the width of each arm. As sheet resistance increased, the optimal value of the spacing between the two arms increased but that of the width of each arm did not happen. However, the efficiency depends strongly on the sheet resistance