PEDOT:PSS-Based Nanofibrous Electrodes for Flexible Transparent Electronics

The demand for flexible and transparent electronics requires electrodes capable of concurrently maintaining high conductivity, flexibility, and optical transparency. Conventional metal electrodes, such as indium tin oxide (ITO), are inadequate for this purpose due to their inherent brittleness and the scarcity of indium. Furthermore, when subjected to bending conditions, ITO on flexible substrates is prone to delamination and cracking. These challenges have urged researchers to explore alternative Transparent Conductive Electrode (TCE) materials exhibiting properties similar to ITO. These targeted characteristics include (1) high conductivity and transparency, (2) exceptional flexibility and stability under various mechanical deformations (4) large area processability, (4) cost-effective, (5) room temperature (RT) processing, and (6) readily available: i.e., abundant supply.<br/><br/>Our work addresses these challenges by introducing a single-step electrospinning process with post-treatment to create highly conductive, flexible, and transparent PEDOT:PSS-based fibers suitable for interconnects and electrodes. These fibrous electrodes exhibit a sheet resistance of 7 Ω/sq and electrical conductivity of 354 S/cm, which is comparable to traditional rigid and metal electrodes, such as copper, silver, and ITO (0.1 to 10 Ω/sq) all while maintaining exceptional optical transparency of 77 % at 550 nm wavelength and excellent flexibility. The previous research has explored PEDOT:PSS and PEDOT:PSS/Ag nanowires fibers with sheet resistance in the range of 600 kΩ/sq and electrical conductivity in the range of 10^-12-10¹ S/cm which is very low and has no potential to replace the conventional electrodes. The electrospun nanofibers were also deposited onto different substrates with varying levels of roughness and subjected to cyclic bending tests. The fibers on the poly(caprolactone) (PCL) substrate performed best under 1000 bending cycles with a slight change in sheet resistance from 7 Ω/sq to 8 Ω/sq, while on cotton fabric and Kapton film, a slight increment was observed.<br/><br/>The nanofibers were demonstrated as interconnects in a simple circuit for powering a light-emitting diode (LED). Even after 1000 bending cycles, the fibers were still able to turn on the LED at the same applied voltage of 2V, despite the slight changes in their sheet resistance. The potential of electrospun nanofibers for replacing metal electrodes was evaluated by fabricating a triboelectric nanogenerator (TENG). The TENG employing the metallic electrode achieved an output voltage of 73.9 V and an output current of 6.7 μA. When the copper electrode on one side was replaced with the nanofibers, the electrical performance of the TENG showed a notable improvement, reaching 77.9 V and 7.1 μA. This work stands out due to the significantly lower sheet resistance and stability under bending cycles which is attributed to the organic-inorganic interactions of our nanofibers, positioning them as ideal for applications including touch interfaces, OLEDs, interactive displays, energy storage, and harvesting. etc.