Open-rear side H-pattern optimization based on 2D computer simulations

Currently, photovoltaic-cell manufacturers are tending to use thinner wafers in order to reduce material costs. A drawback is that thin wafers with a full aluminum (Al) rear coverage suffer from bowing and therefore have an increased chance of breakage. Another consequence of the thinner wafer is that the surface recombination velocity (SRV) of the rear side is getting more important for the overall cell performance. To overcome these problems an open rear side (i.e. partial metal coverage) can be used and the wafer rear surface can be passivated using an appropriate dielectric layer. In this paper, we will focus on a solar cell with silicon nitride passivation on the rear side and an Al H-patterned rear metallization with two bus bars. The aim is a first validation of the solar cell simulation software package Microtec against experiments and to get a better physics understanding of the open rear side cell. We performed a parameter study, where we calculated the standard output parameters like shortcut current (Isc), open-circuit voltage (Voc) and fill factor (FF) for varying device parameters. The parameter space that has been explored is composed of the finger pitch, the finger width, the back surface field (BSF) depth, the aluminum doping concentration in the BSF and the surface recombination velocity (SRV) of the SiNx in between the contacts.