Simultaneous enhancement of conductivity and Seebeck coefficient of PEDOT:PSS by triflic acid treatment for flexible thermoelectric generator

Organic thermoelectric materials are of great interest for development of flexible thermoelectric devices. Two crucial parameters namely conductivity and Seebeck coefficient apparently display a trade-off effect towards optimization of thermoelectric (TE) properties. Dopants normally increase the conductivity of PEDOT:PSS but Seebeck coefficient remains unaffected at around 15-18 mu V K-1. In this work, pre-treatment using triflic acid to PEDOT:PSS solution is employed displaying simultaneous increase in conductivity of 1686 S cm(-1) and Seebeck coefficient of 23.6 mu V K-1. Mechanism of improvements are attributed to the increased order of long-range crystal packing as well as hopping between newly generated DOS. HRTEM and XRD data substantiated the improved crystallinity. Acid treatment induced change of conformation from coil like benzoid to linear quinoid structure as observed by Raman spectra, with increasing level of oxidation based on Raman and UV-vis-NIR spectra. The carrier concentration and mobility increased leading to the power factor of 94 mu W m(-1) K-2. Flexible thermoelectric generator (TEG) device is developed on PET film which generate thermovoltage of 2.0 mV at temperature difference of 15 K.

Automated summary

Organic thermoelectric materials are of great interest for flexible thermoelectric devices. The trade-off effect between conductivity and Seebeck coefficient is observed in PEDOT:PSS. Triflic acid pre-treatment is used in this work to simultaneously increase conductivity and Seebeck coefficient. The improvement is attributed to the increased order of long-range crystal packing and hopping between newly generated DOS. HRTEM and XRD data confirm the improved crystallinity. Acid treatment induces conformational change in PEDOT:PSS molecules, leading to increased conductivity and Seebeck coefficient.