Investigating the stretchability of doped poly(3-hexylthiophene)-block-poly(butyl acrylate) conjugated block copolymer thermoelectric thin films

Organic-based thermoelectric materials have become increasingly popular for their ability to convert waste heat into electricity, coupled with their low processing costs, mechanical flexibility, and non-toxicity, making them an attractive option for wearable electronics. However, there is a lack of direct integration of intrinsically stretchable semiconducting polymers in wearable thermoelectric devices. This study investigates the potential of using poly(3-hexylthiophene)-block-poly(butyl acrylate) (P3HT-b-PBA) copolymers doped with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) to develop stretchable thermoelectric devices. Two PBA block lengths, with number molecular weights (Mn) of 3,000 and 6,000, were compared to pristine P3HT homopolymer. We found that all films exhibited edge-on orientations before and after doping, as determined by GIWAXS analysis. The lamellar distance increases while the π − π stacking distance decreases upon doping, indicating that the dopants preferentially allocate in the side-chain domain. Accordingly, the optimized power factor (PF) of the doped P3HT-b-PBA3k and P3HT-b-PBA6k films are found to be 2.13 and 1.42 μW m−1 K−2, respectively; and the stretchable thermoelectric device comprising P3HT-b-PBA3k and a poly(dimethylsiloxane) (PDMS) substrate demonstrate good stretchability with a high PF of 1.77 μW m−1 K−2 at 50% strain, and a high PF retention 86.3% relative PF after 200 stretch/release cycles. This outstanding performance highlights the feasibility of fabricating stretchable thermoelectric device by using intrinsically stretchable semiconducting polymer. The study presents a promising approach for creating stretchable thermoelectric devices using conjugated/insulating block copolymers combining the thermoelectric properties of P3HT and the intrinsic softness of PBA.