B ← N Unit Enables n-Doping of Conjugated Polymers for Thermoelectric Application

Abstract

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.

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

“…The maximum PF values ( PF max ) is estimated to be 24.80 μW m −1 K −2 (Table 2). This value is higher by three times of magnitude than that of our first report of n‐type organoboron thermoelectric polymer ( PF =0.02 μW m −1 K −2 ) [12a] . Most importantly, the PF value of PBN‐19 is fairly comparable to those of the mainstream solution‐processed n‐type polymer thermoelectric materials [8, 10, 19] .…”

Semiconducting Polymers Based on Isoindigo and Its Derivatives: Synthetic Tactics, Structural Modifications, and Applications

“…h) Reproduced with permission. [ 200 ] Copyright 2020, American Chemical Society. i) Molecular structure of P161 .…”

“…[ 198,199 ] Wang and co‐workers copolymerized isoindigo with donor containing B←N unit to obtain P160 (Figure 13g). [ 200 ] The B←N unit lowered the polymer energy levels and resulted in a more delocalized LUMO than the reference polymer without B←N unit. Moreover, the large pendent substituents on the boron atom and the amorphous nature of the polymer promoted the miscibility of the polymer with the dopant (Figure 13h).…”

“…At the optimal doping concentration of 5 wt%, the doped P160 exhibited electrical conductivity of 9.7 × 10 −4 S cm −1 and power factor of 0.02 µW m −1 K −2 , which were somewhat higher than that of the benchmark N2200 with the same doping level. [ 200 ]…”

“…h) AFM height images of pristine (left), 5 wt% doped (middle), and 30 wt% doped (right) P160 films. h) Reproduced with permission [200]. Copyright 2020, American Chemical Society.…”