Cobalt-Alloyed Interface: Transforming Tunneling-Dominated to Continuous Ag–Si Contact in TOPCon Solar Cells

Over the past decade, Tunnel Oxide Passivated Contact (TOPCon) solar cells have emerged as a leading technology in photovoltaics due to their high conversion efficiency, low degradation, and temperature insensitivity. However, the silver–silicon (Ag–Si) interface in TOPCon cells based on laser-enhanced contact-optimization (LECO) technology faces challenges such as carrier recombination caused by lattice mismatch and high metallization costs. To address these issues, this study introduced cobalt disilicide (CoSi2) particles into the Ag paste to enhance the Ag–Si contact on the boron emitter of the TOPCon solar cells. Through a combination of rapid sintering and LECO treatment, effective Co doping was achieved approximately 150 nm below the boron emitter. A continuous alloying interface consists of a Ag–Co–Si ternary alloy and a Co-doped pseudo-eutectic region. This interface transformed the Ag–Si contact from tunneling-dominated into continuous. Co doping increased the interface potential difference, improving field passivation and reducing carrier recombination. Consequently, the photocurrent in the short-wavelength region was improved, and a relative gain of 2.4% in photoelectric conversion efficiency (PCE) was achieved. This work provides an approach to optimizing Ag–Si contacts, reducing metallization costs, and advancing the performance of crystalline silicon (c-Si) solar cells.