  The coupled spin-valley physics in transition metal dichalcogenides (TMDs)
endows exciton states with valley degrees of freedom, making them promising for
valleytronic applications in TMDs monolayers and/or their heterostructures.
Although the valley dynamics of intralayer and interlayer excitons (IXs) have
been studied, efficient manipulation of valley pseudospins by switching exciton
states remains elusive. Therefore, it is of great importance to effectively
tune the exciton states to obtain practical valley polarization switches for
valley encoding. Here, we demonstrate the electrical switching of exciton
emission with highly variable valley polarization mediated by charged IXs
(CIXs) in the heterostructure of monolayer WS2 and two-dimensional (2D)
perovskite, irrespective of lattice constants, the rotational and translational
alignment. The formation of IXs is identified by photoluminescence excitation
(PLE) and photoluminescence (PL) studies, which can be further electrically
tuned from positively charged to negatively charged depending on the
electrostatic doping level of monolayer WS2. Importantly, we demonstrate an
electrical switching from type two to type one band alignment, manifesting as a
change in the PL profile from CIX to charged intralayer exciton emission. Such
transition induces a large contrast in valley polarization between the two
exciton states, enabling the reversible electrically regulated valley
polarization switch with a maximum ON/OFF ratio of 15.8. Our study provides an
alternative mechanism to achieve valley polarization switching with great
simplicity for valleytronics and the electrical control of exciton species and
associated valley-contrasting physics would further facilitate the development
of optoelectronic and valleytronic devices
