Understanding and controlling exciton properties are important for the design of 2D semiconductors, such as monolayer transition metal dichalcogenides (TMDCs) and 2D halide perovskites (HPs). This paper demonstrates that the widespread strategy used for the exciton engineering of 2D HPs, based on dielectric mismatch, is flawed since dielectric mismatch has very little correlation with exciton properties. For monolayer TMDCs, however, the dielectric mismatch is shown to be more important.
Keywords: 2D perovskite; TMDC monolayer; dielectric confinement; dielectric mismatch; exciton binding energy; metal-halide perovskite.