Copper Pastes for TOPCon Solar Cells Processed Using LECO

Silicon (Si) Photovoltaics (PV) has proven itself as the leading technology in PV and will remain so for the foreseeable future as global production increases to multi-terrawatt levels. To date, the Passivated Emitter Rear Contact (PERC) cell has been the dominant mass-produced technology, however, it has rapidly been superseded by Tunnel Oxide Passivated Contact (TOPCon) cells with its higher efficiency limit. The passivating contact requirements of TOPCon, has also allowed newer developments in cell processing such as the Laser Enhanced Contact Optimization (LECO) to be adopted. The LECO process has been shown to narrow efficiency distributions and increase yield in production. Unfortunately, the TOPCon technology relies on Ag contacts on both sides of the cell, leading to substantially more Ag than the PERC cells. Consequently, Ag will continue to be a costly bottleneck in the growth of the PV industry. This study demonstrates efforts to replace the Ag contacts on TOPCon cells with a screen printable and air fired copper-based paste. Initial efforts replacing the rear contact with copper, have shown the importance of the pastes etching rate and firing conditions on performance, with efficiencies of ~23% being achieved.