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

•A lightweight all-organic nanocomposite is prepared for thermoelectric application.•Realignment of Fermi level through doping enhances the thermoelectric performance.•A highest power factor of 48.21 µW/m.K2 at room temperatures is obtained for the thienothiophene based conjugated polymer/MWCNT nanocomposite. 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.