Defects of monolayer PbI2: a computational study.

PbI2 is highly desired for optoelectronics, particularly as a crucial precursor in the preparation of hybrid perovskites. Multifarious defects of PbI2 have been frequently observed in experiments; however, the origin and impact on its intrinsic properties are not clear currently. Hereby, a systematic study on the defects in PbI2 was performed by first principles calculations. Likely defect structures in both 1T and 1H phases were predicted, and the corresponding formation energies at the neutral and charged states based on the pre-estimated chemical potential of I/Pb were both calculated. At the neutral states, the formation energy of VI is relatively low, which is consistent with the experimental observation. However, at the charged states, VPb seems to be dominant regardless of the chemical potential and contributes more to the conductivity. Compared with the two-dimensional transition metal dichalcogenides, the relatively low formation energy of PbI2 indicates its flexibility and the weak Pb-I interaction. Our DFT calculations bring new insights into understanding the influence of defects on its opto-electrical performance and instruct to suppress the formation of those defects that are deleterious to its performance.