In Situ Electrothermal Heating Reveals the Mechanism of Laser‐Enhanced Front Contacts in TOPCon Solar Cells

Laser‐enhanced contact optimization (LECO) technology can achieve ohmic contacts with low recombination and low resistance while lowering peak sintering temperature. However, the microscopic contact formation mechanism of the Ag gridlines on the boron emitters of the tunnel oxide passivated contact solar cell remains debated, especially regarding nonalloyed regions. This study reveals that the porous structure of Ag grid leads to the formation of two distinct contact structures during LECO: pyramids with Ag–Si alloyed pits and, predominantly, intact glass‐covered pyramids (>75%). In situ electrically biased transmission electron microscopy reveals silver‐containing glass layer formation on an intact pyramid under electrothermal heating, reducing resistance of the structure by 15.4%. The results indicate that silver‐rich colloidal contacts with dense Ag nanoparticles in the glass layer, besides Ag–Si directly alloyed contacts, were optimized during the LECO process. Based on these findings, two contact path formation models are proposed. This work demonstrates quantum tunneling of Ag colloids. It also advances the understanding of the LECO mechanism and electrothermal front‐contact optimization and offers a reference for further efficiency gains.