  Charge transfer in type-II heterostructures plays important roles in
determining device performance for photovoltaic and photocatalytic
applications. However, current theoretical studies of charge transfer process
don't consider the effects of operating conditions such as illuminations and
yield systemically larger interlayer transfer time of hot electrons in MoS2/WS2
compared to experimental results. Here in this work, we propose a general
picture that, illumination can induce interfacial dipoles in type-II
heterostructures, which can accelerate hot carrier transfer by reducing the
energy difference between the electronic states in separate materials and
enhancing the nonadiabatic couplings. Using the first-principles calculations
and the ab-initio nonadiabatic molecular dynamics, we demonstrate this picture
using MoS2/WS2 as a prototype. The calculated characteristic time for the
interlayer transfer (60 fs) and the overall relaxation (700 fs) processes of
hot electrons is in good agreement with the experiments. We further find that
illumination mainly affects the ultrafast interlayer transfer process but has
little effects on the relatively slow intralayer relaxation process. Therefore,
the overall relaxation process of hot electrons has a saturated time with
increased illumination strengths. The illumination-accelerated charge transfer
is expected to universally exist in type-II heterostructures.
