Enhancing the Stability of Perovskite by Constructing Heterojunction of Graphene/MASnI3
In this paper, the geometric and electronic properties of heterojunctions constructed by graphene sheet and MASnI3 surface were investigated by performing first-principles calculations based on the density functional theory. Our results show that the interaction between graphene and MASnI3 surface is in the scope of van der Waals’ interaction. In the heterojunction, electrons transfer from graphene to MASnI3 surface, resulting in the formation of the built-in electric field in the interface, which is favorable for the separation of electrons and holes. The absorption spectra showed that the absorption intensity of the heterojunction in the visible region is slightly smaller than that of pristine MASnI3 surface. The energy barriers of water molecule diffusing through MASnI3 surfaces are relatively low, but when water molecule penetrates the graphene sheet into the interior of the MASnI3 it has to overcome energy barrier of as high as 9 eV. It is found that the water diffusions through the surfaces cause a very severe damage on the structures of graphene sheet and MASnI3 surface. So, the graphene can block the penetration of water into the inside of the material and retard the degradation of the perovskites. Coating a graphene sheet on the MASnI3 surface to form a heterojunction is an effective strategy of enhancing the stability and performance of the perovskite solar cell. This study could provide an in-depth understanding on the properties of graphene/MASnI3 heterojunctions and contribute to design strategy for the perovskite-based solar cells.