Simulation-aided studies on the superior thermoelectric performance of printable PBDTT-FTTE/SWCNT composites

Quasi one-dimensional (1D) carbon nanostructures hybridized with π-conjugated polymeric systems are vastly explored for their unique heat/carrier transport beneficial for thermoelectric (TE) applications. We present the TE response of all-organic composites fabricated with poly[4,8-bis(5-(2-ethylyhexyl)thiophene-2-yl)benzo[1,2-b; 4,5-b']dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)3-fluorothieno[3,4-b']thiophene-)-2-carboxylate-2-6-diyl)] (PBDTT-FTTE) and single-walled carbon nanotube (SWCNT). SWCNTs form strong π-π interfacial interactions with the polymer, and their TE performance is improved through p-doping with ferric chloride (FeCl3). Investigation of the electrical conductivity (σ) and Seebeck coefficient (α) reveals a characteristic mechanism arising from low-energy carrier filtering and Fermi-level pinning. DIGIMAT-MF© material modeling platform simulates σ and thermal conductivity (κ) and indicates a CNT aspect ratio distribution in the system. The doped composite with 55 wt% SWCNT exhibits the maximum ZT value of 0.044 at 303 K using the simulated κ value. A flexible TE generator (TEG) consisting of 21 legs is dispenser printed that produces ∼32.7 nW power output with a 65 K temperature gradient across 15 kΩ load resistance. COMSOL Multiphysics® simulation is used to optimize TEG design for maximum extractable output power.