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

Abstract

Poly-Si/SiO x 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/SiO x 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 ( J 0 ) down to 4.9 fA/cm 2 , low contact resistivity between the Ag contacts and the FPC ( ρ c,m ) down to 7.2 mΩ⋅cm 2 , and Ohmic transport through the FPC including the SiO x film were achieved using wet-chemically grown SiO x . Nevertheless, J 0 of metallized regions ( J 0,m ) exceeded 1000 fA/cm 2 . Reducing J 0,m was attempted by mitigating the blistering observed in FPCs, but J 0,m remained high. With Ni/Ag plating, excellent surface passivation with J 0 down to 2.7 fA/cm 2 and very low J 0,m < 50 fA/cm 2 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 J 0,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. • Fired passivating contacts (FPCs) developed relying only on the thermal budget of firing and not on conventional annealing. • Compatibility of FPCs with fire-through Ag screen-printing and Ni/Ag plating tested. • Screen-printing: J 0,pass ≈ 5 fA/cm 2 & ρ c < 10 mΩ∙cm 2 achieved, but J 0,metal was high. • Plating: J 0,pass < 3 fA/cm 2 & J 0,metal < 50 fA/cm 2 achieved, but contacts were non-Ohmic. • Integration of FPCs in screen-printed large-area n-TOPCon cells led to 18.4% efficiency.