A Chemically Doped Naphthalenediimide‐Bithiazole Polymer for n‐Type Organic Thermoelectrics

The synthesis of a novel naphthalenediimide (NDI)‐bithiazole (Tz2)‐based polymer [P(NDI2OD‐Tz2)] is reported, and structural, thin‐film morphological, as well as charge transport and thermoelectric properties are compared to the parent and widely investigated NDI‐bithiophene (T2) polymer [P(NDI2OD‐T2)]. Since the steric repulsions in Tz2 are far lower than in T2, P(NDI2OD‐Tz2) exhibits a more planar and rigid backbone, enhancing π–π chain stacking and intermolecular interactions. In addition, the electron‐deficient nature of Tz2 enhances the polymer electron affinity, thus reducing the polymer donor–acceptor character. When n‐doped with amines, P(NDI2OD‐Tz2) achieves electrical conductivity (≈0.1 S cm−1) and a power factor (1.5 µW m−1 K−2) far greater than those of P(NDI2OD‐T2) (0.003 S cm−1 and 0.012 µW m−1 K−2, respectively). These results demonstrate that planarized NDI‐based polymers with reduced donor–acceptor character can achieve substantial electrical conductivity and thermoelectric response. A novel naphthalenediimide‐bithiazole n‐type semiconducting polymer [P(NDI2OD‐Tz2)] is synthesized and its structural, thin‐film morphological, as well as charge transport and thermoelectric properties are compared to the parent naphthalenediimide‐bithiophene [P(NDI2OD‐T2)] polymer. The new n‐type polymer has a greater backbone planarity and a reduced donor–acceptor character. N‐doped P(NDI2OD‐Tz2) can reach electrical conductivity and thermoelectric power factor far superior to those of analogous P(NDI2OD‐T2).