Transition of the Type of Band Alignments for All-Inorganic Perovskite van der Waals Heterostructures CsSnBr3/WS2(1-x)Se2x.

In general, two-dimensional semiconductor-based van der Waals heterostructures (vdWHs) can be modulated to achieve the transition of band alignments (type-I, type-II, and type-III), which can be applied in different applications. However, it is rare in three-dimensional perovskite-based vdWHs, and it is challenging to achieve the tunable band alignments for a single perovskite-based heterostructure. Here, we systematically investigate the electronic and optical properties of all-inorganic perovskite vdWHs CsSnBr3/WS2(1-x)Se2x based on density functional theory (DFT) calculation. The calculated results show that the transitions of band alignment from type-II to type-I and type-III to type-II are achieved by modulating the doping ratio of the Se atom in the WS2(1-x)Se2x monolayer for SnBr2/WS2(1-x)Se2x and CsBr/WS2(1-x)Se2x heterostructures, respectively, in which the CsBr and SnBr2 represent two different terminated surfaces of CsSnBr3. The change of band alignments can be attributed to the conduction band minimum (CBM) transforming from the W 5d to Sn 5p orbital in SnBr2/WS2(1-x)Se2x vdWHs, and the valence band maximum (VBM) and CBM change from an overlapped state to a separated one in CsBr/WS2(1-x)Se2x vdWHs. This work can provide a theoretical basis for the dynamic modulation of band alignments in perovskite-based vdWHs.