  Bulk photovoltaic effect, which arises from crystal symmetry-driven charge
carrier separation, is an intriguing physical phenomenon that has attracted
extensive interest in photovoltaic application due to its junction-free
photovoltaic and potential to surpass Shockley-Queisser limit. Whereas
conventional ferroelectric materials mostly suffer from extremely low
photocurrent density and weak photovoltaic response at visible light
wavelengths. Emerging two-dimensional ferroelectric semiconductors with coupled
visible light absorption and spontaneous polarization characteristics are a
promising alternative for making functional photoferroelectrics. Herein, we
report the experimental demonstration of the bulk photovoltaic effect behavior
based on the 2D ferroelectric semiconductor {$\alpha$-InSe caused by an
out-of-plane polarization induced depolarization field. The {$\alpha$-InSe
device exhibits enhanced bulk photovoltaic response in the visible light
spectrum owing to its narrow bandgap. It was demonstrated that the generated
photovoltaic current density was nearly two orders of magnitude greater than
conventional bulk ferroelectric materials. These findings highlight the
potential of 2D ferroelectric semiconductor materials for bulk photovoltaic
applications in a broad spectral region.
