Side-Chain-Free Benzothiadiazole-Based Thermoelectric Polymers with Enhanced Electrical Conductivity and Thermal Stability by Acid Cleavage

Abstract

The presence of insulating side chains in conductive polymers often impedes intermolecular interactions and localizes charge carriers, thereby deteriorating charge transport properties. In this study, side-chain-free benzothiadiazole (BT)-based conductive polymers are synthesized using a thermal-assisted rapid acid cleavage (TRAC) method, which achieves complete removal of silane side chains from the parent polymer and preliminary doping by trifluoromethanesulfonic (TfOH). Remarkably, compared to the parent polymers SiFBT-TT and SiBT-TT, the Hall mobility of FeCl₃-doped FBT-TT increased by sixfold (from 0.16 ± 0.02 to 0.93 ± 0.03 cm² V⁻¹ s⁻¹), while that of FeCl₃-doped BT-TT exhibited a 15-fold enhancement (from 0.11 ± 0.05 to 1.60 ± 0.17 cm² V⁻¹ s⁻¹), due to the intensified backbone packing upon side chain cleavage. Consequently, the FeCl₃-doped BT-TT exhibited an exceptional electrical conductivity of up to 730 S cm⁻¹ and a power factor of 81 µW m⁻¹ K⁻², representing a new benchmark for BT-based conductive polymers. Additionally, the power factors of the side-chain-free polymers remained stable even after prolonged heating at 100 °C for 1000 min, attributed to the strengthened interactions between the highly delocalized backbones and dopant anions. This work provides a new approach to design side-chain-free thermoelectric polymers with both high electrical conductivity and outstanding thermal stability.