A Flexible Organic Thermoelectric Generator with Optimized Interconnects Based on Doped Single-Walled Carbon Nanotube Clays

Organic thermoelectric generators (OTEGs) are promising for wearable low-grade heat harvesting, but their device-level output is often limited by interconnect-induced losses. This study investigates flexible OTEGs based on doped single-walled carbon nanotube (SWCNT) thermoelectric clays and optimizes their interconnect structure. P-type and n-type SWCNT clays were prepared by solution processing using TCNQ and TPP as dopants, respectively, and assembled into a five-pair flexible OTEG. The optimized p-type and n-type clays exhibited Seebeck coefficients of 40.81 and −22.42 μV K−1, respectively. The initial OTEG, in which p-type thermoelectric clay was used as the interconnect, delivered a maximum output power of 16.47 nW at ΔT = 21 K. Replacing this thermoelectric-clay interconnect with a compliant Cu-foil/silver-paste interconnect reduced the internal resistance from approximately 372 Ω to 2 Ω, whereas the open-circuit voltage at ΔT = 21 K increased only modestly from 4.95 to 5.08 mV. Under identical controlled temperature-gradient and load-scanning conditions, the optimized OTEG delivered 3.08 μW at ΔT = 21 K, corresponding to a power density of 356.36 nW cm−2. Mechanical and wrist-worn tests further indicated the flexibility and practical voltage response of the optimized device. These results demonstrate that interconnect optimization is critical for improving SWCNT-clay-based flexible OTEGs.