High Efficiency Screen-Printed Ag-Free PERC Solar Cell With Cu Paste and Laser-Enhanced Contact Optimization

Screen-printable copper (Cu) paste offers a promising, cost-effective plug-and-play alternative for photovoltaic cell metallization. However, the tendency of Cu diffusion into silicon presents a key challenge in maintaining cell performance. This work reports on the use of Bert Thin Films’ screen-printable Cu paste in combination with a postfabrication laser-enhanced contact optimization (LECO) process to significantly improve the stability and performance of Cu-contacted passivated emitter and rear contact (PERC) solar cells. Ag-free Cu-contacted p-PERC solar cell efficiency of 21.4% was achieved with a low series resistance of 0.7 Ω-cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and a fill factor of 79% after the LECO process, which remained essentially stable over 17 days. In addition, LECO-treated cells showed a pseudofill factor (pFF) of 82.4% compared to 80.7% for the untreated cells, indicating that the LECO process not only reduces contact resistance but also mitigates Cu migration toward the junction. The LECO process enables low-temperature firing by restoring the series resistance. Under firing the Cu-contacted screen-printed cells improves the pFF but results in high series resistance and low cell efficiency before the LECO treatment. In contrast, cells without LECO treatment showed an efficiency of 10.7% on day one, which increased to 19.4% after 17 days due to the reduction in series resistance from 9.3 to 1.8 Ω-cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>. This study shows that the synergy between Bert Thin Films’ Cu paste and the LECO treatment significantly narrows the efficiency gap between Cu and Ag-contacted p-PERC cells, paving the way for scalable, high-efficiency, Ag-free solar cells.