n-Type Polymer Semiconductors Based on Conformation-Locked π-Extended Bithieno[3,4-c]pyrrole-4,6-dione (BTPD) Acceptor Units for Organic Thermoelectrics

Abstract

Achieving high electrical conductivity in n-type polymers remains a key challenge in organic thermoelectrics. In this study, two conformation-locked, electron-deficient building blocks (BTPD-BTz and BTPD-TTz) were designed by incorporating simple electron-withdrawing bithiazole (BTz) or thiazolothiazole (TTz) units into a classic bithieno[3,4-c]pyrrole-4,6-dione (BTPD) moiety. These building blocks were polymerized via direct C–H arylation polymerization (DArP) to afford two n-type polymers PBTz-TCN and PTTz-TCN, both featuring ultra low-lying LUMO energy levels down to −4.21 eV. Upon n-doping with N-DMBI, PTTz-TCN exhibited a significantly enhanced electrical conductivity of 7.91 S cm-1 and a power factor of 0.54 μW m-1 K-2—markedly outperforming PBTz-TCN and the benchmark n-type polymer N2200. These results highlight that extending classic electron acceptor units with electron-deficient π-bridges capable of conformational locking is an effective strategy for designing high-performance n-type building blocks for advancing the performance of n-type organic thermoelectric materials.