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Developing polymers with high electrical conductivity (σ) after n‐doping is a great challenge for the advance of the field of organic thermoelectrics (OTEs). Herein, we report a series of thiazole imide‐based n‐type polymers by gradually increasing selenophene content in polymeric backbone. Thanks to the strong intramolecular noncovalent N⋅⋅⋅S interaction and enhanced intermolecular Se⋅⋅⋅Se interaction, with the increase of selenophene content, the polymers show gradually lowered LUMOs, more planar backbone, and improved film crystallinity versus the selenophene‐free analogue. Consequently, polymer PDTzSI−Se with the highest selenophene content achieves a champion σ of 164.0 S cm−1 and a power factor of 49.0 μW m−1 K−2 in the series when applied in OTEs after n‐doping. The σ value is the highest one for n‐type donor‐acceptor OTE materials reported to date. Our work indicates that selenophene substitution is a powerful strategy for developing high‐performance n‐type OTE materials and selenophene incorporated thiazole imides offer an excellent platform in enabling n‐type polymers with high backbone coplanarity, deep‐lying LUMO and enhanced mobility/conductivity. [ABSTRACT FROM AUTHOR]

n‐Type semiconducting polymers with high thermoelectric performance remain challenging due to the scarcity of molecular design strategy, limiting their applications in organic thermoelectric (OTE) devices. Herein, we provide a new approach to enhance the OTE performance of n‐doped polymers by introducing acceptor‐acceptor (A‐A) type backbone bearing branched ethylene glycol (EG) side chains. When doped with 4‐(2,3‐dihydro‐1,3‐dimethyl‐1H‐benzimidazol‐2‐yl)‐N,N‐dimethylbenzenamine (N‐DMBI), the A‐A homopolymer PDTzTI‐TEG exhibits n‐type electrical conductivity (σ) up to 34 S cm−1 and power factor value of 15.7 μW m−1 K−2. The OTE performance of PDTzTI‐TEG is far greater than that of homopolymer PBTI‐TEG (σ=0.27 S cm−1), indicating that introducing electron‐deficient thiazole units in the backbone further improves the n‐doping efficiency. These results demonstrate that developing A‐A type polymers with EG side chains is an effective strategy to enhance n‐type OTE performance. [ABSTRACT FROM AUTHOR]