Superb improvement of boron doping in selective emitter for TOPCon solar cells via boron-doped silicon paste

High concentration and deep p++/n junctions formed by selective boron (B)-doping can effectively reduce interfacial recombination losses and contact resistance at the emitter-metal interface of N-type TOPCon solar cells. In this work, ball milling method and thermal annealing process were adopted to realize the controllable doping of B into Si nanoparticles (NPs). By adjusting the ball milling conditions, two kinds of B-doped Si pastes were successfully prepared using B-doped Si NPs and an organic carrier. According to the simulation results and doping performance of B-doped Si paste, a suitable localized B concentration of p++/n junction was fabricated by the selected thermal diffusion process using screen printing B-doped Si paste onto the Si wafer. The maximum B-doping concentrations of p+ and p++ layers were 1.67 × 1019 and 4.91 × 1019 atoms/cm3 respectively. The depth of p+/n and p++/n junctions was 0.41 and 0.72 μm, respectively. This technology is expected to boost the power conversion efficiency of TOPCon solar cells.