Surface fabrication of metal halide perovskite compounds is a challenging issue to enhance energy conversion efficiency of perovskite solar cells (PSCs). Since they are a multi-layered device and the energy band alignment are not necessarily perfectly matched between the adjacent layers, a buffer layer is expected to bring some beneficial effects by intervening between the layers. Such a layer might also give additional effects on surface passivation, surface protection against device deterioration, etc.

In this presentation, we report our first-principles study of graphene fabrication on metal halide perovskite compounds with some types of lattice defects. The sheet-type material has been experimentally reported to improve photovoltaic action of PSCs. Our interest on lattice defects are due to the experimental report indicating the existence of carrier traps near the surfaces of the perovskite compounds.

The present density functional calculations show that single vacancies arising from a loss of either iodine or lead atoms in methyl ammonium lead iodide can be carrier traps near the surface. The calculations on the system after graphene fabrication of the defective crystal predict that the surface coating would suppress carrier trapping at the lattice vacancies. The detailed numerical analyses clarify that electronic interaction by graphene would be significant for the suppression, and would explain a reason why the graphene fabrication of the surface was successful in the previous experiments.