On composition, structure and gettering in polycrystalline Si passivating contacts for solar cells by atom probe tomography

Doped polycrystalline Si (poly-Si) contacts with a nanoscale SiO_x interlayer have attracted significant interest due to their excellent surface passivation and impurity gettering properties for high-efficiency crystalline Si photovoltaics. However, there remains limited information on their atomic-scale microstructure and the mechanisms governing their strong gettering effects. This work employs atom probe tomography and scanning transmission electron microscopy to investigate 3D atomic interactions among dopants, O and Fe impurities in intrinsic and doped poly-Si structures. Observations unveil a new interfacial feature above the oxide interlayer termed the ‘O-lean’ region, posited to play a critical function in passivation. The quantification of the complex state of atomic clustering of various solute species within poly-Si reveals the first experimental validation of Fe gettering via co-clustering with P₄V clusters and O. These atomic-scale observations provide novel insights into the formation mechanisms and electrical performance of doped poly-Si contacts, offering new strategies for their optimisation.