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Thin polysilicon (poly-Si)-based passivating contacts can reduce parasitic absorption and the cost of n-TOPCon solar cells. Herein, n⁺-poly-Si layers with thicknesses of 30~100 nm were fabricated by low-pressure chemical vapor deposition (LPCVD) to create passivating contacts. We investigated the effect of n⁺-poly-Si layer thickness on the microstructure of the metallization contact formation, passivation, and electronic performance of n-TOPCon solar cells. The thickness of the poly-Si layer significantly affected the passivation of metallization-induced recombination under the metal contact (<i>J</i>_{0,<i>metal</i>}) and the contact resistivity (<i>ρ_c</i>) of the cells. However, it had a minimal impact on the short-circuit current density (<i>J_sc</i>), which was primarily associated with corroded silver (Ag) at depths of the n⁺-poly-Si layer exceeding 40 nm. We introduced a thin n⁺-poly-Si layer with a thickness of 70 nm and a surface concentration of 5 × 10²⁰ atoms/cm³. This layer can meet the requirements for low <i>J</i>_{0,<i>metal</i>} and <i>ρ_c</i> values, leading to an increase in conversion efficiency of 25.65%. This optimized process of depositing a phosphorus-doped poly-Si layer can be commercially applied in photovoltaics to reduce processing times and lower costs.