Increased Series Resistance in the Laser‐Enhanced Contacts of Polysilicon‐Based Solar Cells from an Additional Light Anneal

In the fabrication of silicon solar cells, a light anneal step, performed at moderate temperatures under controlled illumination, is commonly employed after the firing step to promote hydrogen in‐diffusion. This process effectively passivates both bulk and surface defects, improving the open‐circuit voltage and power conversion efficiency of modern silicon solar cells, such as tunneling oxide passivating contact (TOPCon) cells. With the emergence of laser‐enhanced contact technologies, the timing of this light anneal becomes critical to fully harness its benefits. In this study, the impact of an additional light anneal applied after the laser‐enhanced contact process is investigated. This additional light anneal is found to cause a significant increase in series resistance, traced via luminescence imaging and contact resistance measurements to the interface between the metal and p + emitter region. Electrical measurements under varying bias and temperature conditions suggest that the series resistance increase is likely due to excessive hydrogen accumulation at the metal/silicon interface. The possible formation of a thicker glass layer is not observed by microscale characterization, although this possibility can not be ruled out either. These findings underscore the importance of positioning the laser‐enhanced contact process as the final step in the fabrication sequence for high‐efficiency TOPCon solar cells.