Decoupling the Conductivity–Seebeck Trade‐Off in N‐Type MXene/Conjugated Polyelectrolyte Thermoelectric Bilayers

ABSTRACT To decouple the Seebeck coefficient from electrical conductivity in metallic thermoelectric (TE) systems, we investigated bilayer heterostructures of MXene (Ti 3 C 2 T x ) and conjugated polymers with anionic (–SO 3– Na + , CPE‐Na), neutral (CP), and cationic (–N + (CH 3 ) 3 Br–, CPE‐Br) side chains. Strong electrostatic anchoring between the cationic ammonium side chains and electronegative MXene terminations induces a previously unreported Coulombic trap‐induced filtering mechanism, distinct from conventional energy filtering. The resulting localized potential wells selectively trap low‐energy carriers to enhance the Seebeck coefficient, while concurrent lattice stiffening suppresses electron–phonon scattering and preserves high‐energy carrier transport. This decoupling raises Hall mobility from 1.01 to 5.40 cm 2 V −1 s −1 and the Seebeck coefficient from –8.6 to –19.0 µV K −1 while maintaining a metallic conductivity of 5291.9 S cm −1 . The optimized MXene/CPE‐Br film, processed with a halogen‐free solvent, achieves a record power factor of 190.5 µW m −1 K −2 and a peak figure of merit ( zT ) of 0.0279. Strong interfacial adhesion further imparts good electromechanical durability under repeated bending to a flexible TE generator, providing an effective strategy to address the transport limitations of n‐type MXene‐based TE materials.