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 CsSnBr 3 /WS 2(1−x) Se 2x 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 WS 2(1−x) Se 2x monolayer for SnBr 2 / WS 2(1−x) Se 2x and CsBr/WS 2(1−x) Se 2x heterostructures, respectively, in which the CsBr and SnBr 2 represent two different terminated surfaces of CsSnBr 3 . The change of band alignments can be attributed to the conduction band minimum (CBM) transforming from the W 5d to Sn 5p orbital in SnBr 2 /WS 2(1−x) Se 2x vdWHs, and the valence band maximum (VBM) and CBM change from an overlapped state to a separated one in CsBr/WS 2(1−x) Se 2x vdWHs. This work can provide a theoretical basis for the dynamic modulation of band alignments in perovskite-based vdWHs.
Based on the structural characteristics of a molecular wire coupled to electrodes,the electronic tunneling process in a molecular device consisting of such a composite molecule under a bias is modeled by a simplified successive tunneling model with asymmetric multiple potential barriers in series. An analytical expression for the electronic transmission spectrum is obtained. Then,the relations between the transmission coefficient and various parameters,such as the width and height of the barrier,the distance between two neighboring barriers,the effective mass of electron, and the bias voltage, are calculated. It is found that when the electron energies are equal to some special values,obvious resonant tunneling occurs,and the transmission coefficient is very sensitive to the parameters mentioned above. The results presented here suggest that the transport behaviors of molecular electronic devices can be significantly modified in a controlled way, for example,by altering the constituents or/and the configurations of the composite molecule.
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