MWCNT/Thienothiophene based All-Organic thermoelectric composites: Enhanced performance by realigning of the Fermi level through doping

Abstract

Thermoelectric (TE) polymer nanocomposites are an emerging class of functional materials that have immense potential for commercial usage. In this work, a lightweight all-organic nanocomposite of benzodithiophene-thienothiophene (BDT-TTE) based conjugated polymer poly[4,8-bis(5-(2-ethylyhexyl)thiophene-2-yl)benzo[1,2-b;4,5-b’]dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)3-fluorothieno[3,4-b’]thiophene-)-2-carboxylate-2–6-diyl)] (PBDTT-FTTE) and multi-walled carbon nanotube (MWCNT) was prepared for TE applications. The peak electrical conductivity in the composite was obtained with 45 wt% MWCNT content and the resulting composite exhibited a temperature tolerance up to 350 °C. The as-prepared nanocomposite was further p-doped with an oxidizing agent for tuning its Fermi level positioning leading to the further enhancement in TE output. The electrical conductivity was further boosted by 6.7x post-doping with concurrent 2.5x enhancement in the Seebeck coefficient. Thus, the power factor increased from 1.28 µW/m.K2 to 48.21 µW/m.K2, leading to the highest value for the thienothiophene based conjugated polymer/MWCNT nanocomposite. The device performance was demonstrated with a prototype exhibiting the power delivery of ~ 7 nW/cm2 when tested with applied temperature difference across the hot and cold junction of 65 K.