Benzotriazole-based copolymers with an interlocked conformation for mitigating the correlation of thermoelectric parameters

Abstract

As for thermoelectric materials, a strong trade-off relationship between the electrical conductivity (σ) and the Seebeck coefficient (S) is a huge obstacle to maximization of their thermoelectric (TE) performances, especially for polymeric semiconductors with a single component. Recently, some of intensive efforts were made to explore effective methods for decoupling TE parameters of organic semiconductors. In this work, a novel type of D–A non-fused-ring copolymers were designed and synthesized from the Stille coupling polymerization of cyclopentadithiophene and benzotriazole units (fluorinated or non-fluorinated). The incorporation of fluorine atoms into the polymer backbone constructed skillfully a fully interlocked coplanar conformation via the dual assistance of the F···S and N···H noncovalent interactions, significantly enhancing the ordered degree of molecular stacking and thus the σ and S values. More importantly, the two polymers achieved a simultaneous increase in both the σ and S within a certain doping time, probably due to that the bimodal orientation of polymers played a crucial role in decoupling the correlation between σ and S. Consequently, FeCl3-doped P(CPD-BTA-2F) harvested an optimal power factor of 7.77 ± 0.77 μW m−1 K−2, which is one order of magnitude higher than that of P(CPD-BTA). This work, albeit only a modest power factor (PF) was attained, offered a valuable insight into the molecular engineering for breaking through the trade-off relationship between σ and S, and shed some light on the development of promising polymeric TE materials.