The invention relates to a low-
pressure diffusion process applied to polycrystalline
black silicon solar cells, which comprises the following steps: (1) allowing a
silicon wafer to entering a tube; (2) performing constant temperature
processing; (3) performing low temperature oxidation, generating a
thin oxide layer on a surface of the
silicon wafer to make the subsequent
phosphorus source deposition more uniform; (4) performing
low temperature deposition, uniformly depositing a
phosphorus source on the surface of the
silicon wafer; (5) performing high temperature propulsion, allowing the
phosphorus source to diffuse into the silicon wafer, wherein during high temperature propulsion, the temperature is 820-850 DEG C, the
nitrogen flow rate is 1000-3000sccm, the dry
oxygen is 0-1000sccm, the furnace pressure is 50-150mbar, and the time is 10-20 minutes; (6) performing secondary
diffusion, wherein during the secondary
diffusion, the temperature is 800-850 DEG C, the
nitrogen flow rate is1000-3000sccm, the source
nitrogen is 0-400sccm, the dry
oxygen is 0-1000sccm, the furnace pressure is 50-150mbar, the time is 2-10 minutes; (7) performing cooling; (8) performing nitrogen filling, allowing the pressure inside the
pipe to reach the
atmospheric pressure so that a furnace door is opened; and (9) performing discharging. The present invention improves the uniformity of the square resistance after
diffusion of polycrystalline
black silicon.