Multiscale characterization of laser-induced defects in the production of heterojunction photovoltaic cells

Heterojunction (HJT) photovoltaic cells represent a significant advancement in solar technology due to their ability to combine high efficiency with durability. However, the integration of shingling technology, a process which employs precise laser cutting to maximize panel performance, introduces substantial challenges. The utilization of nanosecond infrared (ns-IR) lasers for segmentation often results in structural and morphological damage, particularly along the cut edges, thereby impacting the optical, mechanical, and electrical properties of the cells. This study employs advanced multi-scale characterisation techniques, including scanning electron microscopy (SEM), Raman spectroscopy, photoluminescence (PL) analysis, and atomic force microscopy (AFM), to investigate these laser-induced defects. The results reveal extensive disruptions to the surface morphology, including the formation of silicon oxide residues and deformation of pyramidal structures essential for light trapping. Raman and PL analyses highlight strain and disorder within the silicon lattice, particularly near the cut edges, where defects reduce crystalline quality and increase recombination losses. Additionally, Kelvin Probe Force Microscopy (KPFM) measurements indicate a significant decline in surface potential and work function, extending up to millimeters from the cut region, further compromising cell efficiency. These findings emphasize the critical need to optimize laser cutting processes for HJT cells, particularly in shingling applications. Achieving this objective necessitates minimizing defects and preserving the integrity of silicon and indium tin oxide layers, thereby facilitating the fabrication of high-performing solar cells that can be scaled up for application in more efficient and reliable photovoltaic solutions.