Molecular dynamics simulation is used to investigate the structure characteristics and mechanical properties

and to discuss the vapor deposition of MAPbI3 on the TiO2 substrate under a temperature of 300 K and three precursor compositions of PbI2:CH3NH3I=1:2

1:1 and 2:1

respectively. During the preparation processes

three polyhedral groups including PbI42- tetrahedra

PbI53- pyramids and PbI64- octahedra are produced. After classifying their arrangements and analyzing the distribution of CH3NH3+ cations

early CH3NH3PbI3 nuclei consisting of well-connected PbIx (x=4

5 or 6) polyhedral clusters and sufficient amounts of surrounding CH3NH3+ cations were identified. The influence on early nuclei from the precursor compositions of PbI2:CH3NH3I were discussed. The results show that the calculated values of elastic modulus is in good agreement with the experimental results. The PbI53- pyramids dominate over other polyhedral groups during the vapor deposition simulations. Meanwhile

even though the total amounts of polyhedra have a small dependence on the precursor compositions

the populations of the well-connected clusters and the early nuclei decrease rapidly with increasing the PbI2:CH3NH3I ratio. This is in consistent with the experimental finding which to some degree

adding more CH3NH3I will optimize the device performance.