Insights in the light trapping effect in silicon solar cells with backside diffraction gratings

Light trapping by means of backside diffraction gratings can strongly increase the efficiency in silicon solar cells. However, the optimization of the grating geometry involves comprehensive multiparameter scans, which necessitates an efficient simulation method. In this study, we employ a simulation approach that combines ray tracing with rigorous coupled wave analysis. As an additional benefit, this approach provides a much better physical insight into the light trapping mechanism in contrast to fully electromagnetic simulation methods. The influence of the ray tracing simulation settings in terms of recursion depth and diffraction order on the simulation results is investigated. We show that the choice of a proper recursion depth and a sufficient number of diffraction orders is essential for obtaining fully optimized grating parameters and that the minimum recursion depth required for obtaining the correct optimized grating parameters depends on the silicon thickness. Furthermore, we investigate the influence of the angle of incidence on the optimized grating parameters. As major result, we find that the optimum grating structure does not depend on the angle of incidence on the solar cell.