Vacancy-Driven Sizable Shift Current in Centrosymmetric Materials

The bulk photovoltaic effect (BPVE), which could convert light into direct current, has recently sparked great interest in its potential application in terahertz sensors, solar cells, etc. It has been extensively studied in perfect noncentrosymmetric systems. The introduction of defects is inevitable during the experimental preparation of materials, yet their impact on BPVE has rarely been studied. Here, we illustrate this in two experimentally well-studied centrosymmetric transition metal dichalcogenides (TMDs) systems, monolayer T-PtSe2 and bilayer H-MoS2, in which the BPVE are supposed to be forbidden. Specifically, the introduction of Se vacancies in monolayer T-PtSe2 and S vacancies in bilayer H-MoS2 transforms both systems into C3v symmetry, thus allowing localized shift current generation. Both vacancy–vacancy and bulk–vacancy interactions contribute to the localized shift current, while increasing the vacancy concentrations could enhance the shift current. Notably, the vacancy-generated shift current is giant, which is comparable to those of noncentrosymmetric systems. The van der Waals interlayer interaction could further regulate the shift current magnitude in the defected H-MoS2 bilayer. More interestingly, the direction of the shift current can be managed by patterning the point defect location. Our research provides valuable insight into the role of defects in activating and modulating the BPVE.