Electrospun Nanofiber-Based Electrodes Composed of Core-Shell (PVDF)-(Al) Structures for Application to Flexible Electronics

Nanostructured transparent conductors have been studied intensively for application to flexible and transparent electronic devices. Among diverse nanomaterials, electrospun nanofibers provide several advantages over other nanomaterials, including a high aspect ratio, uniform distribution, and a facile fabrication process. In the present study, an electrode composed of a core-shell (PVDF)-(Al) structured nanofiber mesh film was fabricated via electrospinning and sputtering processes, without any hightemperature heat treatment or wet chemical treatment. A free-standing circular collector was used to form a PVDF nanofiber mesh film, to perform the conformal coating of Al onto the PVDF surfaces. The parameters of the tip-to-collector distance and the electrospinning voltage needed to stably form a PVDF nanofiber mesh film were determined. The sheet resistance of the mesh film was dramatically reduced from 1870 Ω/sq. to 154 Ω/sq. when the sputtering time was increased from 2 min to 4 min, an outcome explained by the changed surface morphology of the Al coating layer. The sheet resistance decreased from 657 Ω/sq. to 15.4 Ω/sq. with an increase in the electrospinning time from 2 min to 8 min due to the increased numbers of nanofibers and junctions. When the transmittance at 550 nm with respect to the sheet resistance was plotted for these mesh films, the graph was divided into the bulk and percolation regimes. Mesh films with transmittance rates that exceeded 85% exhibited sheet resistance that clearly increased with an increase in transmittance, indicating a percolation network. Finally, the durability of the core-shell (PVDF)-(Al) structured nanofiber mesh film was evaluated using a repetitive bending test, the results of which clearly showed superior performance over Al thin film. With inexpensive metal Al, a competitive flexible and transparent electrode was fabricated in the form of a core-shell (PVDF)-(Al) structured nanofiber mesh film.