ABSTRACT
The latest developments in fiber design and materials science are paving the way for fibers to evolve from parts in passive components to functional parts in active fabrics. Designing conformable, organic electrochemical transistor (OECT) structures using poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) fibers has excellent potential for low-cost wearable bioelectronics, bio-hybrid devices, and adaptive neuromorphic technologies. However, to achieve high-performance, stable devices from PEDOT:PSS fibers, approaches are required to form electrodes on fibers with small diameters and poor wettability, that leads to irregular coatings. Additionally, PEDOT:PSS-fiber fabrication needs to move away from small batch processing to roll-to-roll or continuous processing. Here, it is shown that synergistic effects from a superior electrode/organic interface, and exceptional fiber alignment from continuous processing, enable PEDOT:PSS fiber-OECTs with stable contacts, high µC* product (1570.5 F cm-1 V-1 s-1 ), and high hole mobility over 45 cm2 V-1 s-1 . Fiber-electrochemical neuromorphic organic devices (fiber-ENODes) are developed to demonstrate that the high mobility fibers are promising building blocks for future bio-hybrid technologies. The fiber-ENODes demonstrate synaptic weight update in response to dopamine, as well as a form factor closely matching the neuronal axon terminal.
ABSTRACT
The thermoelectric properties of flexible thin films fabricated from two commercial poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) formulations filled with multiwalled carbon nanotubes (MWCNT) and nitrogen-doped MWCNT (N-MWCNT) were investigated. A simple spray-coating method for the fabrication of such flexible films on a polyethylene terephthalate substrate was developed. While increasing the MWCNT concentration had little effect on the thermoelectric properties, increasing the N-MWCNT concentration resulted in the emergence of an overall n-type semiconducting behavior and, thereby, tailoring the Seebeck coefficient of the composite films from p-type to n-type was shown. The Seebeck coefficient of the two PEDOT:PSS formulation films was inverted from 4.1 to -13.3 µV/K and from 12.5 to -10.9 µV/K respectively, with increasing N-MWCNT concentration from 0 to 95 wt.%. The importance of these results for future work stems from the possibility of tailoring the behavior of a typical p-type polymer such as PEDOT:PSS and the effect that the polymer conductive grade has on the switching concentration.
ABSTRACT
Thermoelectric textiles that are able to generate electricity from heat gradients may find use as power sources for a wide range of miniature wearable electronics. To realize such thermoelectric textiles, both p- and n-type yarns are needed. The realization of air-stable and flexible n-type yarns, i.e., conducting yarns where electrons are the majority charge carriers, presents a considerable challenge due to the scarcity of air-stable n-doped organic materials. Here, we realize such n-type yarns by coating commercial sewing threads with a nanocomposite of multiwalled carbon nanotubes (MWNTs) and poly(N-vinylpyrrolidone) (PVP). Our n-type yarns have a bulk conductivity of 1 S cm-1 and a Seebeck coefficient of -14 µV K-1, which is stable for several months at ambient conditions. We combine our coated n-type yarns with poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) dyed silk yarns, constituting the p-type component, to realize a textile thermoelectric module with 38 n/p elements, which are capable of producing an open-circuit voltage of 143 mV when exposed to a temperature gradient of 116 °C and a maximum power output of 7.1 nW at a temperature gradient of 80 °C.
