Enhancing Electrical Conductivity and Power Factor in Poly‐Glycol‐Bithienylthienothiophene with Oligoethylene Glycol Side Chains Through Tris (pentafluorophenyl) Borane Doping

Abstract Doping of organic semiconductors has served as an effective method to achieve high electrical conductivity and large thermoelectric power factor. This is of importance to the development of flexible/wearable electronics and green energy‐harvesting technologies. The doping impact of the Lewis acid tris (pentafluorophenyl) borane (BCF) on the thermoelectric performance of poly(2‐(4,4′‐bis(2‐methoxyethoxy)‐5′‐methyl‐[2,2′‐bithiophen]‐5‐yl)‐5‐methylthieno[3,2‐b]thiophene (pgBTTT), a thiophene‐based polymer featuring oligoethylene glycol side chains is investigated. Tetrafluorotetracyanoquinodimethane (F4TCNQ), a well‐established dopant, is utilized as a comparison; however, its inability to co‐dissolve with pgBTTT in less polar solvents hinders the attainment of higher doping levels. Consequently, a comparative study is performed on the thermoelectric behavior of pgBTTT doped with BCF and F4TCNQ at a very low doping level. Subsequent investigation is carried out with BCF at higher doping levels. Remarkably, at 50 wt% BCF doping level, the highest power factor of 223 ± 4 µW m⁻¹ K² is achieved with an electrical conductivity of 2180 ± 360 S cm⁻¹ and a Seebeck coefficient of 32 ± 1.3 µV K⁻¹. This findings not only contribute valuable insights to the dopant interactions with oxygenated side chain polymers but also open up new avenues for high conductivity thermoelectric polymers in flexible electronic applications.