Highly Conductive Direct-write Electrospun PEDOT: PSS Nanofibers

In this research, fabrication and electrical property of poly(3,4-ethylene dioxythiophene): poly(styrene sulfonate) (PEDOT: PSS) nanofibers, directly patterned using Near-field Electrospinning (NFES), are extensively studied. The PEDOT: PSS have been widely used as an active layer in semiconductors as film form; however, utilizing the polymer as fibers is not widely explored due to difficulties in manufacturing and patterning. To overcome such challenges, PEDOT: PSS ink was mixed with Polyethylene glycol (PEO) polymer and electrospun to precisely pattern the desired shape. In addition, doping of polar solvents was used to enhance the conductivity of PEDOT: PSS fibers. Using this method will be cost-efficient, easy to manufacture, and improve the mechanical properties and electronic performances.<br/>Substantial studies have been made in organic semiconductors to novel technologies due to their lightweight, flexibility, and solution-processability. Nowadays, people demand more portability, mechanical robustness, and scalability for electronic devices, which popularize flexible electronics. Flexible electronics is a device that can change shape by bending, folding, or rolling without degrading its functionalities. These flexible devices have various applications, including displays, sensors, wearable electronics, biomedical devices.<br/>Among many materials used as an active layer on organic semiconductors, PEDOT: PSS arose to be one of the promising materials due to its optical transparency, tunable electrical conductivity, high flexibility, and stretchability, etc. However, PEDOT: PSS films have weak cohesion, which is unreliable for flexible electronics, and have a direct current electrical conductivity of no more than 1.0 S cm^-1. Therefore many studies have been performed to improve its conductivity by several orders of magnitude through doping of polar solvents, strong acids, ionic liquids, etc.<br/>However, PEDOT: PSS studies are mostly limited to films, and fundamental understanding of the material properties about PEDOT: PSS fibers is still lacking. Electrospun fibers have several advantages over films such as excellent mechanical properties, large surface area to volume ratio, high flexibility, and high sensitivity. <br/>Here we present directly patterned PEDOT: PSS nanoscale fibers with enhanced conductivity. PEDOT: PSS fibers conductivity will be compared with doped PEDOT: PSS using Dimethyl sulfoxide (DMSO) and ionic liquid 1-ethyl-3-methylimidazoliumbis(trifluoromethyl sulfonyl)imide (EMIm-TFSI). DMSO is well known for enhancing PEDOT: PSS conductivity due to inter -PEDOT bridging mechanism. The ionic liquid is also used to improve the conductivity by using dopants, which gives a morphology evolution. To precisely pattern PEDOT: PSS fiber Self-Aligning Nanojet (SA-N) will be used as a cost-effective direct-patterning method. SA-N mode is achieved in NFES at the lowest flow rate regime, which relies on surface current-induced electrostatic force rather than hydrodynamic force. As a result, the kinematics of SA-N is controlled by the electric force, which causes the jet’s trajectory to always self-align normal to the substrate’s surface. Therefore, the accurate patterning of nanofiber on multi-dimensional surfaces can be achieved by modulating the stage to follow the profile of the 3D surface.<br/>We will also present a comparison of the conductivity of doped and undoped PEDOT: PSS fibers. Moreover, electrical characterization of the precisely patterned PEDOT: PSS fibers on graphene will be analyzed. We believe that precise patterned PEDOT: PSS fibers with boosted conductivity will provide an effective method to manufacture next-generation flexible and stretchable electronics.