Acceptor–acceptor (A‐A) copolymerization is an effective strategy to develop high‐performance n‐type conjugated polymers. However, the development of A‐A type conjugated polymers is challenging due to the synthetic difficulty. Herein, a distannylated monomer of strong electron‐deficient double B←N bridged bipyridine (BNBP) unit is readily synthesized and used to develop A‐A type conjugated polymers by Stille polycondensation. The resulting polymers show ultralow LUMO energy levels of −4.4 eV, which is among the lowest value reported for organoboron polymers. After n‐doping, the resulting polymers exhibit electric conductivity of 7.8 S cm−1 and power factor of 24.8 μW m−1 K−2. This performance is among the best for n‐type polymer thermoelectric materials. These results demonstrate the great potential of A‐A type organoboron polymers for high‐performance n‐type thermoelectrics.
Only very few conjugated polymers can be n-doped for thermoelectric applications. In this work, for the first time, we report that incorporation of Boron−Nitrogen coordination bond (B ← N unit) to a donor−acceptor (D−A) type conjugated polymer enable ndoping for thermoelectric application. The incorporation of B ← N unit into the polymer backbone leads to not only a downshift of LUMO/HOMO energy levels by 0.27 eV/0.33 eV, but also diminished intramolecular D−A character of the polymer backbone. As a result, while the control polymer cannot be n-doped, the polymer containing B ← N unit (PI-BN) can be n-doped by 4-(1,3-dimethyl-2,3-dihydro-1H-benzoimidazol-2-yl)-N,N-dimethylaniline (N-DMBI). Finally, PI-BN exhibits an electrical conductivity (σ) of 0.97 × 10 −3 S cm −1 , Seebeck coefficient (S) of −453.8 μV K −1 , and power factor (PF) of 0.02 μW m −1 K −2 when doped with 5 wt % N-DMBI. A great advantage of PI-BN is its excellent miscibility with the ndopant because of its amorphous nature and large pendent substituents. This work indicates that organoboron polymers can be ndoped and can be used for thermoelectrics.
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