The pn junction for solar cell was prepared on p-type Si wafer by the furnace using the POCl₃ and oxygen mixed precursor to research the characteristic of interface at pn junction. The sheet resistance was decreased in accordance with the increasing the diffusion process time for n-type doping on p-type Si wafer. The electron affinity at the interface in the pn junction was decreased with increasing the amount of n-type doping and the sheet resistance also decreased. Consequently, The efficiency and fill factor were increased at the solar cell with the sheet resistance of 35 ~ 40ohm/sqr. The highest efficiency was 12.33% at the solar cell textured by the KOH solution.