Disorder‐Controlled Efficient Doping of Conjugated Polymers for High‐Performance Organic Thermoelectrics

Abstract

Molecular doping of conjugated polymers (CPs) is critical to improve their electrical properties in organic thermoelectric materials, which are promising candidates for low‐temperature energy harvesting and self‐powered sensors. Because excessive dopants are used in the doping process, securing highly crystalline CPs by suppressing dopant‐induced disorder is crucial. Recently, tris(pentafluorophenyl)borane (BCF) has attracted interest as a strong Brønsted acid dopant that enables efficient integer charge transfer by forming a complex with water. However, the crystalline ordering of BCF‐doped CPs has not been properly controlled; the resultant thermoelectric performance is therefore still lower than other p‐doped CPs prepared by conventional redox doping. Here, an efficient doping strategy is proposed with BCF to attain highly doped CPs with dramatically suppressed structural and energetic disorder. In a non‐polar aliphatic solvent, hexane, BCF can effectively diffuse into poly[2,5‐bis(3‐tetradecylthiophen‐2‐yl)thieno[3,2‐b]thiophene] (PBTTT) via sequential doping, leading to remarkable electrical conductivity and power factor of 230 S cm−1 and 140 µW m−1 K−2, respectively. In addition, sequentially doped films exhibit highly delocalized transport characteristics owing to the low degree of charge carrier localization within their high solid‐state ordering. The results provide an approach for disorder‐tolerant doping strategies with a systematic investigation of structure–property relationships in highly doped CPs.