Brush-Paintable Black Electrodes for Poly(vinylidene fluoride)-Based Flexible Piezoelectric Devices.

We investigated simple and unrestricted brush-paintable black electrodes for poly(vinylidene fluoride) (PVDF)-based artistic flexible piezoelectric devices. The conductive black ink for paintable electrodes was synthesized by mixing poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) and typical black ink and optimizing the mixing ratio. At an optimal mixing ratio, the brush-paintable black electrodes showed a sheet resistance of 151 Ω/sq and high coatability for flexible piezoelectric devices. Noticeably, higher black ink ratios increased adhesion forces, while diminished the shear flow of the conductive black ink. In addition, the optimized conductive black electrode exhibited an outstanding level of mechanical flexibility due to good adhesion between the black electrode and the PVDF substrate. During the repeated inner/outer bending fatigue tests with high strain, no resistance change confirmed the outstanding flexibility of the brush-paintable conductive electrode. As a promising application of the brush-paintable optimized black electrode, we suggested highly flexible piezoelectric devices that can be used. A PVDF-based piezoelectric speaker and a generator with the brush-paintable black electrode showed acoustic and output signal values approximate to those of metallic electrodes fabricated by vacuum-based high-cost thermal evaporators. Our experiment demonstrated a cost-efficient and simple process for fabricating brush-paintable electrodes, applicable to the flexible PVDF-based piezoelectric devices.