Electrostatic Spraying Deposition of Transparent Polyvinylidene Fluoride Films for Optoelectronic Application

Highly transparent piezoelectric polyvinylidene fluoride (PVDF) films on soda-lime-silica slide glasses within the visible spectral range were prepared through electrostatic spraying deposition. The coating solution was prepared by dissolving PVDF pellet in dimethylformamide (DMF) and mixing at 60 °C for 12 h to obtain a clear sol. To investigate the crystallinity, surface morphology, transmittance within the visible spectral range, and piezoelectric properties of the films when varying the electrostatic spraying conditions, the heating temperatures during electrostatic spray deposition were varied at 90 °C, 120 °C, 150 °C and 180 °C. In addition, β-phase-dominant films coated at above 120 °C, as confirmed through X-ray diffraction analysis, showed a piezoelectric response (open-circuit voltage across the top and bottom electrodes) using a digital oscilloscope. However, the optical transmittance of the films heated at 180 °C was close to 60% within the visible spectral range owing to the inhomogeneous and rough surface microstructure. From the result of the piezo-response, the OCV of the PVDF films heated at 180 °C reached 0.75 V, where only 0.30 V was observed for the PVDF heated at 90 °C. Ferroelectricity combined with the optical transmittance of PVDF confirmed that the film is an attractive option for optoelectronic applications.