Bandgap Modulation in Flexoelectricity-Enhanced Photovoltaic Effect of PVDF Film Under Bending Deformation

Flexoelectricity-enhanced photovoltaic (FPV) effect has emerged as one of the significant research interests. In this investigation, we found it for the first time that the bandgap modulation effect played a critical role on the FPV effect of poly (vinylidene fluoride) (PVDF)-based polymer films. By using the ultraviolet-visible- near Infrared (UV-Vis-NIR) absorption spectra, we demonstrated that bending strain results in pronounced and reversible bandgap modulation. Specifically, concave bending (compression strain, ITO electrode on top of PVDF film) results in −86 meV bandgap narrowing in the PVDF (28 µm) film, whereas convex bending (tensile strain) causes bandgap widening of +97 meV. For polarized PVDF films, the samples showed comparable shifts of −88 meV and +114 meV under concave bending and convex bending conditions, respectively. The observed behavior is attributed to dipole reorientation and changes in interchain electronic coupling induced by mechanical deformation. These findings provide new insights into strain–electronic coupling mechanisms in ferroelectric polymers and highlight the potential of these materials for strain-tunable flexible electronic and optoelectronic applications.