First-principles study of shift current mechanism in low-dimensional inversion-broken systems

Bulk photovoltaic effect, characterized by the generation of a steady photocurrent without the aid of external p-n junction, has attracted a lot of attention because of its potential as a high-performance solar energy harvester. We perform ab initio simulations to obtain the real-time photocurrent, and investigate underlying electronic origin of the photocurrent generation mechanism in organic molecular solids (TTF-CA), hybrid halide perovskite (MAPbI3 and FAPbI3), and transition metal dichalcogenides (TMDs). We show the photovoltaic nature can be associated with the interchain charge shifting mechanism in TTF-CA. For hybrid halide perovskite, though both the ferroelectric polarization and the nonzero bulk photocurrent are prototypical manifestation of the broken inversion symmetry, we investigate that the photovoltaic nature is not necessarily associated with the ferroelectricity, but is rather determined by the intrinsic electronic band properties near the Fermi level. By considering one-dimensional TMD nanotubes we examine the effect of dimensionality, beyond the broken inversion symmetry, on the generation mechanism of photocurrent. We find that the nanotube structure can produce substantially larger shift current as observed in experiment. We suggest that the real-time analysis of the photocurrent can provide a better understanding of the bulk photovoltaics, beyond the widely used perturbation schemes.