Advancing Flexibility and Sunlight Absorption of Two-Dimensional Janus Heterojunctions of MXY/Graphene (M = Mo, W; X = S, Y = Se)

van der Waals (vdW) heterojunctions with rich interfacial properties and unique photophysical properties have become the focus of nanoscience due to their great potential applications in high-frequency optoelectronic devices and the flexible equipment field. Herein, the mechanical and optoelectronic properties of vdW heterojunctions composed of Janus materials and graphene (MXY/graphene, M = Mo, W; X = S, Y = Se) are investigated systematically. It has been proved that the significant charge transfer at the interface of these materials promotes carrier separation effectively, and the light absorption coefficients reach more than 105 cm–1 in the visible range, especially for the vdW heterojunction graphene/MoSSe (Se–C) with a luminous flux as high as 23.5 mA cm–2, all of which have superior electrical conductivity and optical properties. Meanwhile, for the vdW heterojunction WSSe/graphene, the band gap of graphene can be pulled apart up to 85.1 meV. Moreover, their low Young’s modulus indicates their suitability for flexible optoelectronic devices. This work could not only reveal the performance differences of vdW heterojunctions consisting of Janus materials and graphene at two different heterojunction interfaces but also provide a theoretical basis for the design of high-frequency optoelectronic devices.