Flexoelectricity-enhanced photovoltaic effect in flexible LiNbO3 nanorod array/PVDF nanocomposites

Abstract

Recently, the flexoelectricity-enhanced photovoltaic effect has gained significant scientific attention. In this investigation, we successfully fabricated vertically aligned LiNbO₃ nanorod (LN-NR) arrays and mixed them with a PVDF (polyvinylidene difluoride) solution to produce LN-NR/PVDF nanocomposites. The flexoelectric coefficient measurement results indicate that the LN-NR/PVDF-91 (91% LiNbO₃) nanocomposite has the largest flexoelectric coefficient μ₁₃₃ of 4.95 × 10⁻⁸ C m⁻¹, which is approximately 9-fold that of the pristine PVDF film. The light polarization dependence of the photovoltaic current measurement on an LN-NR/PVDF-91 nanocomposite demonstrated that the increase of photovoltaic (PV) current arises from the flexoelectric effect. Furthermore, the photovoltaic current (I_pv) of the LN-NR/PVDF composites was measured for various nanomaterials. It was revealed that the I_pv of the flat LN-NR/PVDF-67 (0.65 μA cm⁻²) nanocomposite increased by 13.8-fold compared with that of the LN-nanoparticles/PVDF-67 nanocomposites (43.8 nA cm⁻²). Next, the photovoltaic current (I_pv) of the LN-NR/PVDF composites was measured at various curvatures. The data indicate that at a downward bending curvature of 20 m⁻¹, the I_pv of the LN-NR/PVDF-91 composites increases by 88% to 1.88 μA cm⁻² compared to that of the composite under flat conditions. In contrast, the I_pv of the LN-nanosheets/PVDF-67 nanocomposite (71.3 nA cm⁻²) only increased by 21.21% to 86.3 nA cm⁻² at a curvature of 20 m⁻¹ compared with that of the flat state of the LN-nanosheets/PVDF-67. This demonstrated that the shape of LN nanomaterials can strongly influence the photovoltaic current of LN/PVDF nanocomposites, mainly due to the increase of the flexoelectricity of aligned LN-nanoparticles/PVDF nanocomposites. The DFT (density functional theory) calculation results indicate that the bending process can generate a piezoelectric coefficient e₃₅ of 0.038 C m⁻² at a curvature of 20 m⁻¹. Therefore, LN-nanorods/PVDF nanocomposites show great potential application prospects in the non-destructive readout of ferroelectric memory devices.