A Distannylated Monomer of a Strong Electron‐Accepting Organoboron Building Block: Enabling Acceptor–Acceptor‐Type Conjugated Polymers for n‐Type Thermoelectric Applications

Abstract

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.

An n-type narrow-bandgap organoboron polymer with quinoidal character synthesized by direct arylation polymerization

“…The new absorption band is attributed to the polaron-induced electronic transitions after n-doping. 32,45 The n-doping behavior of PBN-TP is further confirmed by the EPR spectra (Fig. 5b).…”

“…There is no EPR signals in the pristine film; however, strong signals appeared in the doped film, suggesting that unpaired electrons are present in the doped film. 32,46 The UV-vis-NIR absorption and EPR results confirm the effective n-doping behavior of PBN-TP. On the other hand, no obvious change was observed for PBN-T films in both UV-vis-NIR absorption and EPR spectra before and after n-doping (Fig.…”

“…26 A family of D–A type conjugated polymers based on BNBP unit has been synthesized and has been successfully used in high-performance OSCs, 27–29 organic indoor photovoltaics, 30 OFETs, 31 and organic thermoelectrics. 32 However, these polymers always exhibit a medium bandgap larger than 1.8 eV and show absorption in the visible range. In this work, we aim to develop narrow bandgap n-type conjugated polymers based on BNBP by copolymerizing with quinoidal structures.…”

Recent Developments of n‐Type Organic Thermoelectric Materials: Influence of Structure Modification on Molecule Arrangement and Solution Processing

“…Although the performance (PF=0.02 μW m −1 K −2 ) was not as good as previously reported other structures, it provided a new way of molecule design. In 2021, Wang and co‐workers prepared the electron‐accepting building block through B←N unit, [45] obtaining two A–A polymers (PBN‐18 and PBN‐19). The LUMOs of two polymers were inferior to 4.0 eV (−4.43 eV for PBN‐18, −4.03 eV for PBN‐19).…”

“…In 2021, Wang and co-workers prepared the electron-accepting building block through B ! N unit, [45] obtaining two A-A polymers (PBN-18 and PBN-19). The LUMOs of two polymers were inferior to 4.0 eV (À 4.43 eV for PBN-18, À 4.03 eV for PBN-19).…”