Conformationally locked polythiophene processed by room-temperature blade coating enables a breakthrough of the power factor

Abstract

Thiophene-based simple polymers are the most investigated p-type organic thermoelectric (OTE) materials thanks to their readily tunable structure and low-cost synthesis. However, it is difficult for them to achieve high mobility and power factor (PF) through common film fabrication. Herein, two new polymers, PTTE-TVT and PTE-TVT, were developed by combining conformationally locked ester-substituted thiophenes with a thienothiophene (or thiophene) spacer and highly coplanar thienylenevinylene (TVT). The difference in the conformational lock pattern and spatial geometry induced by subtle regulation of the spacer resulted in quite different backbone conjugation, intermolecular stacking, carrier mobility and final OTE performance. Owing to better backbone conjugation and bilateral side-chain arrangement, PTTE-TVT achieved preferable stacking, with a high hole mobility of 0.54 cm² V⁻¹ s⁻¹ (6-times that of PTE-TVT) and excellent doping efficiency, ultimately achieving a conductivity of 302 S cm⁻¹, PF_max of 189.9 μW m⁻¹ K⁻² and ZT of 0.12. Moreover, polymer films were prepared by convenient blade coating, which led to ordered films and enabled application of large-area flexible devices. The obtained PF was the highest value for polythiophene with easy, room-temperature film fabrication. Our results demonstrated that the synergistic molecular design and blade-coating protocol could be used to further improve the thermoelectric performance for simple polymers.