  We report experimental investigations of spin-to-charge current conversion
and charge transfer dynamics (CT) at the interface of graphene/WS$_2$ van der
Waals heterostructure. Pure spin current was produced by the spin precession in
the microwave-driven ferromagnetic resonance of a permalloy film
(Py-Ni$_{81}$Fe$_{19}$) and injected into the graphene/WS$_2$ heterostructure
through the spin pumping process. The observed spin-to-charge current
conversion in the heterostructure is attributed to inverse Rashba-Edelstein
effect (IREE) at the graphene/WS$_2$ interface. Interfacial CT dynamics in this
heterostructure was investigated based on the framework of core-hole-clock
(CHC) approach. The results obtained from spin pumping and CHC studies show
that the spin-to-charge current conversion and charge transfer process are more
efficient in the graphene/WS$_2$ heterostructure compared to isolated WS2 and
graphene films. The results show that the presence of WS$_2$ flakes improves
the current conversion efficiency. These experimental results are corroborated
by density functional theory (DFT) calculations, which reveal (i) Rashba
spin-orbit splitting of graphene orbitals and (ii) electronic coupling between
graphene and WS$_2$ orbitals. This study provides valuable insights for
optimizing the design and performance of spintronic devices.
