Theoretical study on the tunable electronic band structure of CsPbICl/CsPbBr halide perovskite heterostructure driven by ferroelectric polarization modulation.

Ferroelectric polarizationhas been considered to be an key factor to tune the structural and photoelectric properties of perovskites and their heterostructures. While there has been growing researches made in the novel phenomena originating from interface formed between oxide perovskites, the effects of ferroelectric polarization on the electronic properties of halide perovskites and their heterostructures are rarely studied. Herein, by using first-principles calculations, all-inorganic halide perovskite heterostructure composed of 3D perovskite tetragonal CsPbBr and 2D Ruddlesden-Popper (RP) perovskite CsPbICl is constructed for disclosing the relationship between the intrinsic polarization of tetragonal CsPbBr and electronic band structure of heterostructure. Cs atoms and Pb atoms of tetragonal CsPbBr in heterostructure are artificially moved away from the equivalent centers to simulate increased polarization. Our results show that with the spontaneous polarization of tetragonal CsPbBr increasing, the bandgap of heterostructure decreases, and the band alignment switches from staggered type-II to broken-gap type-III. Moreover, large cation-anion displacements along z-direction in tetragonal CsPbBr can be observed when tensile strains (≥5%) are applied, indicating a increased ferroelectric polarization, which also facilitates the decreasing of bandgap in heterostructure and the type-II-type-III transition of band alignment. Our study suggests that control over the polarization of ferroelectric materials is of great importance to tune the photoelectric properties of perovskite-based devices.