Band edge engineering of CsPbI3 by surface decoration of halogen and alkaline atoms

The inorganic halide perovskite, CsPbI₃, has emerged as a promising material for photovoltaic applications. Effective strategy to tune its band edges is crucial to realize rational interface design with charge transport layers. In this work, by first-principle calculations, we found that surface decoration with halogen and alkaline atoms can effectively tune the electronic properties of CsPbI₃. The introduction of these adatoms breaks the centrosymmetry of the CsPbI₃ surface, resulting in the intrinsic electric dipole whose direction is determined by the charge transfer between the adatoms and the surface. The electric dipole then leads to a lateral electric field which redistribute the conduction and valence band edges to two opposite surfaces with a large electrostatic potential difference. Therefore, the electron and hole carriers are spatially separated, with the energy levels of band edges significantly shifted. Our work demonstrates surface decoration of halogen and alkaline atoms can effectively tailor the band edges of CsPbI₃ and unveils the critical role of induced electric dipole moments, offering new opportunities for optimizing CsPbI₃-based solar cell interfaces.