Enhanced Thermoelectric Performance of Dithienopyrrole and Thienoisoindigo-Based Conjugated Polymers by Introducing Thiophene Spacers.

Donor-acceptor (D-A) conjugated polymers hold significant potential as high-potential thermoelectric (TE) materials due to their adjustable structures, efficient charge transport ability and tunable doping level. However, achieving a balance between the Seebeck coefficient (S) and electrical conductivity (σ) remains challenging. In this work, we employ thienoisoindigo (TIIG) as the acceptor and dithieno[3,2-b:2',3'-d]pyrrole (DTP) as the donor to construct two novel D-A conjugated polymers for TE application. Through introducing thiophene (T) units as spacers between DTP and TIIG, PTIIG-2T-DTP enhances the planarity of conjugated backbones compared to PTIIG-DTP. Moreover, PTIIG-2T-DTP film shows more compact packing between conjugated backbones, which improves the charge transport. Despite slightly lower doping efficiency, doped PTIIG-2T-DTP exhibits superior carrier mobility and conductivity to PTIIG-DTP. Additionally, PTIIG-2T-DTP shows a higher Seebeck coefficient at same doping concentration. Ultimately, PTIIG-2T-DTP achieves a large power factor of 23.2 µWm-1 K-2 with σ of 120 S cm-1 which is much higher than that of PTIIG-DTP. This work develops an effective polymer backbone engineering strategy for developing high-performance D-A conjugated TE polymers.