Industrial metallization of fired passivating contacts for n-type tunnel oxide passivated contact (n-TOPCon) solar cells

Poly-Si/SiOx passivating contacts enable the manufacturing of highly-efficient Si solar cells, but their fabrication commonly relies on an extra high-temperature process such as dopant diffusion or thermal annealing for achieving excellent passivation and contacting properties. This extra process is eliminated in the fired passivating contact (FPC) approach used for simplified fabrication of poly-Si/SiOx passivating contacts. Instead, FPCs rely on the thermal budget of the fast/short and high-temperature firing process used for metallization of solar cells to achieve similar final properties. Despite this, compatibility of FPCs with industrially viable metallization techniques has not been demonstrated yet, which is studied in this work for fire-through Ag screen-printing and Ni/Ag plating. With screen-printing, low recombination current density (J0) down to 4.9 fA/cm2, low contact resistivity between the Ag contacts and the FPC (ρc,m) down to 7.2 mΩ⋅cm2, and Ohmic transport through the FPC including the SiOx film were achieved using wet-chemically grown SiOx. Nevertheless, J0 of metallized regions (J0,m) exceeded 1000 fA/cm2. Reducing J0,m was attempted by mitigating the blistering observed in FPCs, but J0,m remained high. With Ni/Ag plating, excellent surface passivation with J0 down to 2.7 fA/cm2 and very low J0,m < 50 fA/cm2 were achieved, but no Ohmic contacts could be obtained. Integration of screen-printed FPCs in large-area n-TOPCon solar cells was also demonstrated, yielding average efficiencies of 18.4%, limited mainly by the high J0,m and series resistance of the FPCs. The results presented reveal the challenges for the industrialization of FPCs and provide valuable insights for tackling these.