Mitigation of Firing-induced Degradation in Rear Junction Double-side TOPCon Solar Cells by Laser-Enhanced Contact Optimization (LECO)

We present a 23.2% efficient large area (M2), n-type rear junction (RJ) selective double-side tunnel oxide-passivated contact (DS-TOPCon) solar cell featuring a patterned n-TOPCon (poly-Si finger) on the front and full-area p-TOPCon on the rear. A subsequent laser-enhanced contact optimization (LECO) process on the finished cell significantly reduced the contact resistivity of the textured n-TOPCon and the planar p-TOPCon to as low as 0.5 and 3.2 mΩ-cm2, respectively. This notable improvement in ρc was found to be nearly independent of the initial state of the contact. Therefore, the optimal firing temperature after the LECO process shifted toward the lower bound of the tested range (700°C), suppressing firing-induced degradation in surface passivation and minimizing metal-induced recombination. By combining the LECO process with low-temperature firing, we achieved an efficiency of 23.2% (Voc: 710 mV, Jsc: 40.2 mA/cm², FF: 81.3%), demonstrating the effectiveness of this approach in simultaneously enhancing passivation and contact properties. Further optimization in the LECO process, including the development of specially formulated low glass frit Ag paste (for LECO purpose), have the potential to further push the performance boundaries of selective DS-TOPCon solar cells.