Strain tunable photovoltaic efficiency and symmetry breaking enhanced photocurrent in Janus WSTe/BP heterostructures

Janus transition metal dichalcogenides (TMDs) break the inversion symmetry of conventional TMDs and introduce an out of plane dipole moment and built in electric field, which effectively tailor electronic structures and carrier transport features for high performance optoelectronic devices. Using first principles calculations, we investigate two stacking configurations of Janus WSTe and boron phosphide (WSTe/BP) van der Waals heterostructures under biaxial strain ranging from -8% to +8%. Both stacking configurations exhibit robust dynamical and thermodynamic stability as well as typical type II band alignment, with bandgaps of 1.23 eV (TeWS/BP) and 0.67 eV (SWTe/BP). The weaker interfacial dipole in TeWS/BP enables strain driven band alignment transitions, while SWTe/BP preserves type II behavior due to strong interlayer electronic coupling. TeWS/BP delivers a maximum power conversion efficiency (PCE) of 20.98% under +2% tensile strain, far outperforming the 5.26% PCE of SWTe/BP. Combined with nonequilibrium Green’s function simulations, the photogalvanic effect reveals that asymmetric contacts drastically boost the armchair direction photocurrent of TeWS/BP to 18.0 a₀²/photon, about 360 times that of symmetric contacts, with a maximum polarization extinction ratio reaching 327.2. These results clarify stacking and electrode effects on device performance and highlight Janus WSTe/BP as a promising platform for next generation photovoltaics and photodetectors.