Synergistic Tuning of Doping Efficiency and Charge Transport in n-Type Thermoelectric Polymers via Rational Backbone Design

Despite the growing interest in organic thermoelectrics, n-type polymers generally exhibit lower performance than their p-type counterparts, limiting the development of efficient thermoelectric generators. Herein, we report two new n-type polymers based on cyanothiophene-flanked diketopyrrolopyrrole (<b>CDPP</b>) copolymerized with either diketopyrrolopyrrole (<b>PCDPP-DPP</b>) or dialkoxybithiazole (<b>PCDPP-BTzOR</b>) to investigate the critical yet scarcely explored role of orbital interaction between counits in governing thermoelectric performance. Although <b>PCDPP-BTzOR</b> exhibits a more conformationally locked backbone, higher molecular weight, comparable film crystallinity, and nearly identical LUMO level to <b>PCDPP-DPP</b>, the latter displays markedly superior charge transport and doping response. <b>PCDPP-DPP</b> achieves higher field-effect electron mobility (0.191 vs 0.013 cm² V^-1 s^-1) and carrier concentration after n-doping (1.4 vs 1.0 × 10²⁰ spins cm^-3), yielding over an order of magnitude higher electrical conductivity (25.71 vs 1.97 S cm^-1). These improvements arise from the deliberate tuning of interunit orbital interactions in <b>PCDPP-DPP</b>, which promotes electronic delocalization and mitigates trapping associated with polarized charge-transfer states. Consequently, <b>PCDPP-DPP</b> attains a high power factor of 23.52 μW m^-1 K^-2 and a promising room-temperature figure of merit of ZT = 0.07. Overall, this work establishes orbital interaction engineering as an effective strategy for designing high-performance n-type thermoelectric polymers.