In transition metal dichalcogenide (TMDC) heterostructures, interlayer coupling plays a crucial role in the design and emergence of diverse properties. Here, we show the control of the interlayer coupling in Janus WSSe/WS2 heterostructures by changing the stacking order. Low-frequency Raman measurements revealed that heterostructures with the S/S interface show strong interlayer coupling compared to those with the S/Se interface. In the case of the S/S interface, photoluminescence (PL) from WS2 was quenched due to charge transfer in the type-II band alignment, while, interestingly, in the case of the S/Se interface, it was enhanced. The stacking-order dependence of the interlayer coupling and photoluminescence are attributed to the direction of interfacial electric field caused by broken out-of-plane mirror symmetry in a WSSe layer. In the case of the S/S interface, the interfacial electric field promotes the charge transfer as evidenced by strong PL quenching. On the contrary, in heterostructures with the S/Se interface, the charge transfer is blocked as the electric field prevents carrier transfer and modulates the band offset. Our results clearly show that Janus TMDCs with intrinsic fields can be effectively used to manipulate the interlayer interactions and optical properties in heterostructures.
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