Electric Field Modulation and Ultrafast Photogenerated Electron-Hole Dynamics in MoSe2/WSe2 van der Waals Heterostructures

Understanding the non-equilibrium dynamical processes in two-dimensional (2D) transition metal dichalcogenide (TMDC) heterostructures is essential for elucidating their photoelectric behaviors. In this work, we investigate the electronic structure, electric field modulation, and transient optical performance of the MoSe2/WSe2 heterostructure using first principles and nonadiabatic molecular dynamics (NAMD) methods. Applying an external electric field effectively modulates the bandgap and band arrangement of MoSe2/WSe2 heterostructure, along with a transition from indirect to direct bandgap during which the type-II band alignment can be maintained. Specifically, the ultrafast interlayer photogenerated electron transfer time is 72 fs, and the interlayer electron-hole recombination time can be as long as 357 ns, which is longer than that of the intralayer recombination in the constituent monolayers (110 ns for MoSe2 and 288 ns for WSe2), yielding an ultrahigh charge separation efficiency of up to 99.99%. The significant time difference in the processes of photoinduced charge transfer and recombination can be attributed to the corresponding different nonadiabatic coupling averaged values, mainly determined by the electron–phonon coupling and energy difference. The carrier dynamics mechanism revealed in the MoSe2/WSe2 heterostructure is conducive to the development of 2D ultrafast optoelectronic devices.