Direct/indirect band gap tunability in van der Waals heterojunctions based on ternary 2D materials Mo_1-x W _x Y₂

Artificial van der Waals (vdW) heterojunctions assembled by atomically-thin two-dimensional (2D) materials have demonstrated new physical phenomena and unusual properties, thus triggering new electronic, optoelectronic, valleytronic and photocatalytic application. Herein, the electronic band structures of different vdW heterojunctions based on ternary Mo_1-x W _x Y₂ (Y  =  S, Se; x  =  0-1) monolayer with five stacking orders (AA, AA[Formula: see text], A[Formula: see text]B, AB, AB[Formula: see text]) have been investigated using first principle calculations. The direct/indirect band gap has been obtained in the AA[Formula: see text] stacking type-II heterojunctions, ranging from 0.538 eV to 1.260 eV, that are determined by the interlayer distances and stoichiometries. The estimated power conversion efficiency of the AA[Formula: see text] stacking type-II heterojunction varied from 9.1% to 23.4%. The type-I heterojunctions have also been predicted when semiconducting 2H-MoTe₂ monolayer stacks with the specific Mo_1-x W _x Se₂ monolayer, which are MoTe₂/Mo_0.25W_0.75Se₂ and MoTe₂/Mo_0.5W_0.5Se₂. The reported theoretical results can provide broader 2D materials design possibility for the functional devices.