Promising bulk photovoltaic effect in breathing-kagome lattice Nb3TeX7 (X = I, Cl) monolayers

The breathing-kagome lattice materials, distinguished by their captivating electronic structures alongside ferroelectric, ferromagnetic, and nonlinear optical properties, have stimulated considerable interest. Herein, we showcase the promising bulk photovoltaic effect that mainly stems from the Nb breathing-kagome layer in Nb3TeX7 (X = Cl, I) monolayers. Nb3TeCl7 monolayer and Nb3TeI7 monolayer demonstrate the largest corresponding negative shift currents σyyy of −50 and −41 μA/V2, respectively, and maximum positive values of 45 and 41 μA/V2, respectively. The shift current and bandgap in Nb3TeCl7 monolayer are slightly higher than those in Nb3TeI7 monolayer, while Nb3TeI7 monolayer exhibits more pronounced Rashba spin-splitting behavior. Intriguingly, the shift current σyyy could be further enhanced by employing external strain to tune the breathing-kagome Nb-trimer network, while a concurrent decrease in the bandgap occurred under biaxial compressive strain. These findings indicate that the breathing-kagome lattice monolayers of Nb3TeX7 possess considerable potential as promising candidates for future photoelectric applications.