An n‐Type Conjugated Polymer with Low Crystallinity for High‐Performance Organic Thermoelectrics

Abstract

Conjugated polymers (CPs) with low molecular packing order are promising candidates for application in organic thermoelectrics (OTEs), particularly in flexible devices, because the disordered structures can effectively accommodate dopants and ensure robust resistance to bending. On the other hand, n‐doped CPs usually exhibit inferior thermoelectric performance, restricting the development of high‐performance thermoelectric generators. Herein, we report an n‐type CP (ThDPP‐CNBTz) by alternating two acceptor units of thiophene‐flanked diketopyrrolopyrrole and cyano‐functionalized benzothiadiazole. ThDPP‐CNBTz shows a low‐lying LUMO level below ‐4.20 eV and features low crystallinity, enabling the attainment of high doping efficiency. Moreover, the dual‐acceptor molecular design enhances polaron delocalization, thereby improving the thermoelectric performance of the polymer. After n‐doping, ThDPP‐CNBTz exhibits an electrical conductivity (s) of 50.6 S cm‐1 and a power factor (PF) of 126.8 μW m‐1 K‐2, which ranks among the highest reported for solution‐processed n‐type CPs to date. Additionally, solution‐processed flexible OTE device employing doped ThDPP‐CNBTz achieves a PF of 70 μW m‐1 K‐2. Meanwhile, the flexible OTE devices present remarkable resistance to bending strain, with marginal change in σ after 600 bending cycles. The findings presented in this work will advance the development of n‐type CPs for OTE devices, with a particular focus on flexible properties.