Active control of bulk photovoltaic effect in CuInP2S6 via flexoelectric engineering

Bulk photovoltaic effect (BPVE) offers an interesting approach to generate a steady photocurrent in a single-phase material under homogeneous illumination, and it has been extensively investigated in ferroelectrics exhibiting spontaneous polarization that breaks inversion symmetry. Flexoelectricity breaks inversion symmetry via strain gradient in the otherwise nonpolar materials, enabling manipulation of ferroelectric order in the absence of electric field. Combining these two effects together, we demonstrate active mechanical control of BPVE in suspended 2-dimensional CuInP 2 S 6 (CIPS) that is ferroelectric yet sensitive to electric field, which enables practical photodetection devices with order of magnitude enhancement in performance. It is found that the suspended CIPS exhibits 20-fold increase in photocurrent, which can be continuously modulated by either mechanical force or light polarization angle. The flexoelectrically engineered photodetection device, activated by air pressure and without any optimization, possesses a responsivity of (2.45 x 10 -2 ) A/W and a detectivity of (1.73 x 10 11 ) Jones, which are superior to ferroelectric-based photodetection and comparable to the commercial Si photodiode.