Grid Optimization of Tunnel Oxide Passivated Back Contact Silicon Solar Cells

Abstract

Integration of passivating contacts and back contact technologies is the prospective roadmap of crystalline silicon solar cells exceeding 27% efficiency. Allocating both polarities of metal electrodes to the rear surface increases design complexity and manufacturing challenges. While maximizing conversion efficiency, reducing Ag paste consumption is crucial for cost-effectiveness at scale. A systematic methodology is presented for the optimization of metal grid design of silicon back contact solar cells applying tunnel oxide passivated contact (TBC) at the rear surface. Width, thickness, and pitch of fingers, busbars, and contact pads are taken into consideration for the estimation of cell efficiency and Ag paste consumption. The correlation between cell efficiency and Ag paste consumption of TBC solar cells using pad-based or zero-busbar (ZBB) design is analyzed and compared. The ray tracing simulation shows that decreasing finger pitch improves light-generated current density. In pad-based grid design, cell efficiency is enhanced by increasing busbar width, busbar number, and pad number, whereas a large busbar number is essential in zero-busbar design. ZBB TBC cells are estimated to have at least 0.1% absolute efficiency higher than pad-based counterparts. Greater efficiency gain is expected if the Ag paste consumption is limited to below 10 mg W⁻¹.