All-Solution-Processed Polythiophene/Carbon Nanotube Nanocomposites Integrated on Biocompatible Silk Fibroin Substrates for Wearable Thermoelectric Generators

This paper presents proof-of-concept all-solution-processed wearable thermoelectric generators made of single-walled carbon nanotube/poly(3-hexylthiophene) (SWCNT/P3HT) nanocomposites integrated with biocompatible silk fibroin substrates and Ag nanowires (NWs)/poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT/PSS) layers. Since well-dispersed SWCNT/P3HT nanocomposites are obtained through π–π interactions between conjugated backbones, continuous and repeated spraying/vacuum processes enabled the silk fibroin-substrated SWCNT/P3HT films to exhibit an optimized power factor of 204 ± 4.6 μW m–1 K–2 at 50 °C, an electrical conductivity of 1170 ± 52.8 S cm–1, and a Seebeck coefficient of 41.8 ± 0.9 μV K–1, which are ∼1.5 times those of the glass-substrated device. This may be attributed to the significantly enhanced conductivity caused by the increased junction density of the SWCNT bundles within the compact and dense SWCNT/P3HT nanocomposites. When a spray-patterned Ag NWs/PEDOT/PSS electrode was assembled, the constructed in-plane SWCNT/P3HT thermoelectric generators with 14 legs produced an open-circuit voltage (Voc) of 22.6 mV and a peak power of 25.1 nW at a temperature difference (ΔT) of 28.8 °C while maintaining good flexibility during bending tests. This demonstrates that these silk fibroin-substrated thermoelectric generator prototypes, which are worn on the forearm, can be used to harvest human body heat, thereby generating a Voc of ∼6.1 mV with a ΔT as low as 8.3 °C between the skin and surrounding air. This study offers a promising strategy for exploiting simple solution-processed thermoelectric nanocomposites assembled using biomass-based substrates and patterned electrodes for low-grade waste heat-harvesting wearable devices.