  Perovskite solar cells have achieved a substantial breakthrough via advanced
interface engineerings. Reports have emphasized that combining the hybrid
perovskites with Lewis base and graphene improve the performance; the
underlying mechanisms are not yet fully understood. Here, using density
functional theory, we show that upon the formation of CH3NH3PbI3 interfaces
with three different Lewis base molecules and graphene, the binding strength
with S-donors thiocarbamide and thioacetamide is higher than with O-donor
dimethyl sulfoxide, while the interface dipole and work function reduction tend
to increase from S-donors to O-donor. Furthermore, we provide evidences of deep
trap states elimination in the S-donor perovskite interfaces through the
analysis of defect formation on CH3NH3PbI3(110) surface, and of stability
enhancement by estimating activation barriers for iodine atom migrations. These
theoretical predictions are in line with the experimental observation of
performance enhancement in the perovskites prepared using thiocarbamide.
