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 (M_n) 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-PBA_3k and P3HT-b-PBA_6k films are found to be 2.13 and 1.42 μW m⁻¹ K⁻², respectively; and the stretchable thermoelectric device comprising P3HT-b-PBA_3k 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.