Current thermoelectrics technologies dominated by inorganic materials can efficiently harvest low-grade waste heat and realize electrical energy conversion; however, their toxicity, rigidity and energy-intensive processing limit their wide applications. Organic thermoelectrics (OTE) that have the advantages of mechanical flexibility, material abundance and low-temperature and low-pressure processing, are great alternatives.
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. We investigated 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. F4TCNQ, a well-established dopant was 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 was performed on the thermoelectric behavior of pgBTTT doped with BCF and F4TCNQ at a very low doping level. Subsequent investigation was carried out with BCF at higher doping levels. Remarkably, at 50wt% BCF doping level, we achieved the highest power factor of 223 ± 4 µW/m K² with an electrical conductivity of 2180 ± 360 S/cm and a Seebeck coefficient of 32 ± 1.3 µV/K. Our 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.

Nan (Louise) Chen

Johns Hopkins University

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