Seebeck Coefficients of Poly(3,4-ethylenedioxythiophene):Poly(styrene\nsulfonate) Correlated with Oxidation Levels

Abstract

Oxidation\nstates of poly­(3,4-ethylenedioxythiophene):poly­(styrene\nsulfonate) (PEDOT:PSS) were controlled by the electrode potential,\nand its thermoelectric properties were studied elaborately as a function\nof the oxidation level measured by potential-step chronocoulometry.\nWith an increase in the oxidation level from 0.07 to 21%, electrical\nconductivities (σ) were increased from 0.37 × 10^–3 to 1.1 S cm^–1, accompanying a slight decrease\nin the Seebeck coefficient (<i>S</i>) from 79 to 28 μV\nK^–1. Addition of ethylene glycol or dimethyl sulfoxide\nto PEDOT:PSS enhanced σ values but led to a decrease of <i>S</i>. Both σ and <i>S</i> values of the solvent-added\nPEDOT:PSS films became sensitive to the oxidation level, and double\nlogarithmic plots of <i>S</i> and the oxidation level were\nfound to fit a straight line with a slope of −0.25.