Flexoelectricity-enhanced photovoltaic effect in trapezoid-shaped NaNbO₃ nanotube array composites

In this work, we successfully prepared vertically aligned NaNbO₃ nanotube (NN-NT) with trapezoidal shapes, in which the orthorhombic and monoclinic phases coexisted. According to the structure analysis, the NN-NT/epoxy composite film had excellent flexoelectric properties due to the lattice distortion caused by defects and irregular shape. The flexoelectric effect is the greatest in the vertical direction in the flexible NN-NT/epoxy composite film, and the flexoelectric coefficient ( ${\mu }_{12}^{\mathrm{\prime }}$) is 2.77 × 10⁻⁸ C·m⁻¹, which is approximately 5-fold higher than that of the pure epoxy film. The photovoltaic current of the NN-NT/epoxy composite film increased from 39.9 to 71.8 nA·cm⁻² in the direction of spontaneous polarization when the sample was bent upward due to the flexoelectricity-enhanced photovoltaic (FPV) effect. The flexoelectric effect of the NN-NT/epoxy composite film could modulate the photovoltaic response by increasing it by 80% or reducing it to 65% of the original value. This work provides a new idea for further exploration in efficient and lossless ferroelectric memory devices.