▎ 摘　　要

Janus transition metal dichalcogenides attracts increasing attention because the out-of-plane mirror symmetry is broken. Here, using the first-principles methods based on density functional theory, the structural and electronic characteristics of monolayer Janus XPtY (X/Y = S, Se or Te, and X = Y) and their van der Waals heterojunctions (vdWHs) with monolayer and bilayer graphene have been systematically investigated. Monolayer Janus SePtS, TePtS and TePtSe are semiconductor with indirect band gaps of 1.94, 1.05 and 0.72 eV, respectively. Interestingly, the different stacking configuration can induce different contact type (n-type, p-type Schottky contact and Ohmic contact). Moreover, the Schottky barrier height (SBH) and type of contact in the vdWHs can be adjusted by applying an external electric field (E-field). These findings in this paper are expected to provide useful guidance for the design of new nanodevices based on the vdWHs of Janus XPtY and graphene.