Enhanced shift current in GeTe/SnSe heterostructures for bulk photovoltaic effect

We investigate the bulk photovoltaic effect (BPVE) in van der Waals heterostructures composed of group-IV monochalcogenide monolayers (MX, M = Ge, Sn; X = S, Se, Te) using first-principles calculations. While individual monolayers often suffer from a trade-off between band-gap magnitude and optical absorption, we demonstrate that the GeTe/SnSe heterostructure overcomes this limitation through interfacial coupling. Our results reveal a significantly enhanced shift current conductivity, with peak values exceeding 3mA ⋅ Å/V 2 . Crucially, the heterostructure maintains a predominantly positive shift current response across the visible spectrum, avoiding the cancellation effects commonly found in monolayers. Under AM1.5 illumination, the short-circuit current density is enhanced by more than 136% and 158% along two orthogonal directions compared with the individual monolayers. Furthermore, we show that interlayer sliding acts as a robust switch for the photovoltaic response, capable of reversing the photocurrent direction by modulating the evolution of the shift vector. These findings highlight the critical role of symmetry engineering in stacked van der Waals systems and propose a viable route toward high-efficiency shift-current photovoltaics.