Interface Symmetry and Electrostatic Stabilization of Strain-Resilient Janus Heterobilayers for Flexible Piezotronics.

The electronic structure of conventional two-dimensional transition metal dichalcogenides (TMDs) is highly sensitive to lattice deformation, often leading to indirect-to-direct band-gap transitions that compromise performance in flexible nanoelectronic applications. Janus TMDs, with their broken mirror symmetry and intrinsic out-of-plane dipoles, offer a promising alternative platform for electrostatic tuning. However, their electronic stability under strain and the role of the chalcogen-stacking sequence in their heterostructures remain poorly understood. Here, we study the strain tolerance and piezoelectric properties of MoSSe/WSSe heterobilayers from first principles. By examining different configurations, we demonstrate that the interface chemistry strongly modulates interlayer coupling, dynamic charge redistribution, and dipole interactions. Importantly, the combined effects of intrinsic electric fields and interface electrostatics effectively suppress the strain-induced band-gap transitions typical of conventional TMDs. Moreover, while the in-plane piezoelectric response remains nearly insensitive to the stacking order, the shear piezoelectric coefficient depends heavily on the interfacial symmetry and can be effectively tuned by strain modulation. Our results highlight interfacial engineering as a powerful route to design strain-resilient Janus heterostructures for next-generation flexible optoelectronic, valleytronic, and piezotronic devices.