Nanopinhole Passivating Contact Si Solar Cells Fabricated with Metal‐Assisted Chemical Etching

Monocrystalline Si (c‐Si) solar cells with passivating contacts based on doped polycrystalline Si (poly‐Si) on ≈2.0 nm silicon oxide (SiOx) require >1000 °C thermal processing to create conducting pinholes in the SiOx layer. However, this high thermal budget can induce bulk defects in the Czochralski c‐Si wafers used as the cell absorber layer. In this work, it is demonstrated that pinholes can instead be created using metal‐assisted chemical etching on planar or textured morphologies, at room temperature. This wet process creates up to 200 nm wide conducting pinholes that are directly observed with transmission electron and atomic force microscopies. High‐performance hole‐selective poly‐Si/SiNy/SiOx and electron‐selective poly‐Si/SiOx passivating contacts are fabricated and implemented in laboratory‐scale solar cells. This process development significantly broadens the range of passivation layer materials, their thicknesses, and surface morphologies, which enables the design of poly‐Si contacts with superior passivating quality. Using nano‐galvanic corrosion principles, fabrication of polycrystalline Si on silicon nitride/silicon oxide passivating contacts for Si solar cells is demonstrated. These contacts achieve recombination parameter