Efficient Metallization of P-Type Polysilicon in Bifacial TOPCon Structure Silicon Solar Cells Enabled by Ag–Ga Alloy

The development of bifacial tunnel oxide passivated contact (TOPCon) structure crystal silicon (c-Si) solar cells presents significant challenges, particularly regarding the metallization of p-type polysilicon (poly-Si (P)). The Al-containing Ag paste to achieve low contact resistivity atop poly-Si (P) may generate Ag–Al super spikes after sintering, penetrating the poly-Si (P) and degrading surface passivation. This study investigates gallium (Ga) as an alternative element alloying with Ag for poly-Si (P) metallization by mimicking screening-printing conducting paste with a facile thermal evaporation process at the proof-of-concept level. The enhanced doping concentration on the poly-Si (P) surface due to the Ga diffusion and the GaO_x interlayer with high negative fixed charge density would facilitate the transport of holes from poly-Si (P) to the metal electrode, resulting in a low contact resistivity of 1.72 mΩ cm². Besides, since the solid solubility of Si in Ga is significantly lower than that in Al, it is highly likely to avoid any overly grown spikes at the high-temperature sintering process. These findings provide valuable insights for developing effective poly-Si (P) metallization strategies in bifacial TOPCon structure c-Si solar cells by incorporating Ga into industrial screen-printed pastes.