First Principles Calculations on 2D Heterojunctions and Optical Transition Mechanisms of Perovskite MAPbI3

We have employed the first-principle calculations to investigate the interfaces of 2D materials in the first part. The considered 2D materials are graphene and its derivatives, MoS2 and hexagonal boron nitride. These 2D materials can be stacked horizontally or vertically. Both of them show special properties and would have some special applications. We research graphene-based horizontal junctions, MoS2-based horizontal junctions and graphene/h-BN/graphene vertical junctions. For horizontal junctions, we focus on Schottky barrier heights, i.e., band alignments. For vertical ones, they can be applied as tunneling junctions; hence band alignments under electric fields are important. This junction can be potentially used in the nanoelectronics. Secondly, we investigate the optical transitions of perovskite MAPbI3. This material is widely used in the active layer of the solar cell device currently because of the strong absorption near visible-light region and the high power conversion efficiency of the device. Therefore, the optical transition near visible-light region would be the key factor. The band-resolved absorption density analysis is applied to investigate the optical transition mechanism.