High‐Performance and Ecofriendly Organic Thermoelectrics Enabled by N‐Type Polythiophene Derivatives with Doping‐Induced Molecular Order

The ability of n‐type polymer thermoelectric materials to tolerate high doping loading limits further development of n‐type polymer conductivity. Herein, two alcohol‐soluble n‐type polythiophene derivatives that are n‐PT3 and n‐PT4 are reported. Due to the ability of two polymers to tolerate doping loading more significantly than 100 mol%, both achieve electrical conductivity >100 S cm−1. Moreover, the conductivity of both polythiophenes remains almost constant at high doping concentrations with excellent doping tunability, which may be related to their ability to overcome charging‐induced backbone torsion and morphology change caused by saturated doping. The characterizations reveal that n‐PT4 has a high doping level and carrier concentration (>3.10 × 1020 cm−3), and the carrier concentration continues to increase as the doping concentration increases. In addition, doping leads to improved crystal structure of n‐PT4, and the crystallinity does not decrease significantly with increasing doping concentration; even the carrier mobility increases with it. The synergistic effect of these two leads to both n‐PT3 and n‐PT4 achieving a breakthrough of 100 in conductivity and power factor. The DMlmC‐doped n‐PT4 achieves a power factor of over 150 µW m−1 K−2. These values are among the highest for n‐type organic thermoelectric materials. The doping‐induced molecular order changes the crystal structure of polythiophene and the carrier mobility increases with the increase of carrier concentration. The synergistic effect of the two causes the electrical conductivity and power factor to exceed 100. This research points out a direction to advance the development of high‐performance n‐type organic thermoelectric materials.