Selenium‐Driven Charge Delocalization in Conjugated Polymers Enables High Thermoelectric Performance †

Comprehensive Summary Achieving high electrical conductivity through doping without compromising the Seebeck coefficient remains a fundamental challenge in organic thermoelectrics, owing to the intrinsic trade‐off between the two parameters. Here, we propose a rational molecular design strategy to enhance the charge delocalization by substituting thiophene with selenophene in donor‐acceptor (D‐A) type of conjugated polymers based on benzo[1,2‐ b :4,5‐ b' ]dithiophene (BDT) and diketone‐functionalized benzo[1,2‐ c :4,5‐ c' ]dithiophene (BDD) units. The selenophene substitution, combined with backbone planarization via a phenyl substituent, increases the charge localization length from ~7 nm to ~11.5 nm. These structural modifications result in a significant improvement of electrical conductivity, from ~78 S cm –1 to ~148 S cm –1 , while maintaining a high Seebeck coefficient, leading to a maximum power factor exceeding 130 μW·m –1 ·K –2 . These results highlight selenium‐driven charge delocalization as a promising approach to modulating charge transport and guide the molecular design of efficient organic thermoelectrics.