High‐Performance, Air‐Stable Field‐Effect Transistors Based on Heteroatom‐Substituted Naphthalenediimide‐Benzothiadiazole Copolymers Exhibiting Ultrahigh Electron Mobility up to 8.5 cm V−1 s−1

: Rational heteroatom engineering is applied to develop high-performance electron-transporting naphthalenediimide copolymers. Top-gate field-effect transistors fabricated from selenophene-containing polymers achieve an ultrahigh electron mobility of 8.5 cm2 V-1 s-1 and excellent air-stability. The results demonstrate that the incorporation of selenophene heterocycles into the polymers can improve the film-forming ability, intermolecular interaction, and carrier transport significantly.