Research Article: Interlayer‐State‐Coupling Dependent Ultrafast Charge Transfer in MoS2/WS2 Bilayers

Date Published: April 24, 2017

Publisher: John Wiley and Sons Inc.

Author(s): Jin Zhang, Hao Hong, Chao Lian, Wei Ma, Xiaozhi Xu, Xu Zhou, Huixia Fu, Kaihui Liu, Sheng Meng.

http://doi.org/10.1002/advs.201700086

Abstract

Light‐induced interlayer ultrafast charge transfer in 2D heterostructures provides a new platform for optoelectronic and photovoltaic applications. The charge separation process is generally hypothesized to be dependent on the interlayer stackings and interactions, however, the quantitative characteristic and detailed mechanism remain elusive. Here, a systematical study on the interlayer charge transfer in model MoS2/WS2 bilayer system with variable stacking configurations by time‐dependent density functional theory methods is demonstrated. The results show that the slight change of interlayer geometry can significantly modulate the charge transfer time from 100 fs to 1 ps scale. Detailed analysis further reveals that the transfer rate in MoS2/WS2 bilayers is governed by the electronic coupling between specific interlayer states, rather than the interlayer distances, and follows a universal dependence on the state‐coupling strength. The results establish the interlayer stacking as an effective freedom to control ultrafast charge transfer dynamics in 2D heterostructures and facilitate their future applications in optoelectronics and light harvesting.

Partial Text

First principle calculations of MX2 vertical heterostructures were performed using density functional theory implemented in the Vienna ab initio simulation package45 with Perdew, Burke, and Ernzerhof (PBE) generalized gradient approximation for the exchange–correlation functional.46, 47 Because of the absence of strong chemical bonding between layers, van der Waals density functional in the opt88 form48 was employed for structural optimization. Both lattice constants and atomic positions were relaxed until all residual forces remain less than 10−2 eV Å−1 and the total energy variation is less than 10−4 eV. The Brillouin zone was sampled by a set of 25 × 25 × 1 k‐mesh with an energy cutoff of 400 eV for plane waves. The thickness of vacuum layer was set to be larger than 15 Å, so that interactions between repeated images are avoided. Formation energy (E) of the MoS2/WS2 heterostructure is defined as E=(EMoS2/WS2− EMoS2− EWS2)/N, where EMoS2/WS2, EMoS2, EWS2 are, respectively, the total energies of MoS2/WS2 bilayers, MoS2 and WS2 layers, and N is the number of atoms in the supercells.

The authors declare no conflict of interest.

 

Source:

http://doi.org/10.1002/advs.201700086

 

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