摘要： Perovskite solar cells have brought tremendous research interests because of their tolerance of defects, low cost, and facile processing. In perovskite solar cells devices, PbI2 has been utilized to passivate defects at perovskite films surface and grain boundaries, yet a systematic mechanism of PbI2 situ-passivating for enhancing the efficiency has not been fully explored. Here, this work systematically studies the role of the precise PbI2 ratio, and the PbI2 situ-passivation mechanism based on trap density, carrier lifetime, and Fermi level etc. This study finds that the appropriate ratio of I:Pb is around 2.57:1 using energy dispersive spectroscopy. After the moderate excess PbI2 situ-passivating, the trap density is reduced from 6.12 × 1016 cm-3 to 3.38 × 1016 cm-3, and the carrier lifetime is extended from 168.35 ps to 368.77 ps by using femtosecond transient absorption spectroscopy. This result indicates that the moderate excess PbI2 situ-passivation can reduce the trap density and suppress non-radiative recombination. The efficiency of solar cell has realized a nearly 11.3% improvement of 19.55% for the I:Pb ratio of 2.57:1 compared with 2.69:1. It demonstrates that the efficiency can be enhanced effectively by PbI2 situ-passivation.