A Simple Quinoid Building Block for Polymer Semiconductors with Tunable Polarity and High n‐Type Thermoelectric Performance

Abstract π‐Conjugated polymers with deep‐positioned lowest unoccupied molecular orbital (LUMO) level and large electron mobility are highly pursued as n‐type organic thermoelectric materials. Herein, we synthesized a simple structured electron‐deficient quinoid building block, thieno[3,2‐ b ]thiophene‐2,5‐dione (TTD), via one step from a low‐cost starting material. Based on TTD, polymers PQD and PQTD were successfully developed, featuring remarkably low‐lying LUMO levels (−3.91 eV for PQD and −3.73 eV for PQTD), which greatly facilitate n‐doping process. Unexpectedly, it was found that charge carrier polarity of PQD and PQTD can be tuned from p‐type to ambipolar and finally to n‐type in organic field‐effect transistors after thermal treatment, an unprecedented phenomenon in polymer semiconductors. Organic thermoelectric devices based on n‐doped PQD films showed an excellent electrical conductivity up to 19.1 S cm −1 and a power factor of 36.7 µW m −1 K −2 . To the best of our knowledge, this PF value ranks the highest reported to date for n‐doped quinoid‐based polymers. This work underscores the great potential of structurally simple and readily accessible electron‐deficient quinoid TTD for the development of high‐performing n‐type polymer semiconductors.