Enhancement of the thermoelectric properties of PEDOT:PSS via one-step treatment with cosolvents or their solutions of organic salts

Abstract

Thermoelectric (TE) materials that can directly convert heat into electricity are of significance for sustainable development. Organic TE materials have attracted extensive attention owing to their abundance of elements, low material processing cost, high mechanical flexibility and intrinsically low thermal conductivity. In the organic TE family PEDOT:PSS is the most promising material. In this work, we report a facile approach to enhance the TE properties of PEDOT:PSS through a treatment with cosolvents of organic solvents and water or solutions consisting of cosolvents and organic salts. When PEDOT:PSS films are treated with a cosolvent of 80 vol% dimethylformamide (DMF)–20 vol% water, the electrical conductivity and Seebeck coefficient can reach 1055 S cm⁻¹ and 22.3 μV K⁻¹, respectively, leading to an optimal power factor of 52.5 μW m⁻¹ K⁻². The TE performance becomes even higher after a treatment with a solution of a cosolvent and organic salt. After being treated with a solution of 0.1 M methylammonium iodide in 80 vol% DMF–20 vol% water, the PEDOT:PSS films can exhibit an electrical conductivity of 1831 S cm⁻¹, a Seebeck coefficient of 28 μV K⁻¹, and a power factor of 144 μW m⁻¹ K⁻². This is the highest power factor ever achieved for PEDOT:PSS via a one-step post-treatment. The enhancement in the TE properties can be attributed to the synergetic effects of the organic solvents and water during the cosolvent treatments and effects of the salt and cosolvents during the solution treatments. The treatments can increase the charge mobility of the PEDOT:PSS films by partially depleting PSS from PEDOT:PSS and causing the conformational change of PEDOT chains.