have been reported in inorganic ionic solids [ 15 ] and electrolytes, [ 16,17 ] where ions are the only charge carriers. But to the best of our knowledge, the ionic thermoelectric effect in conducting polymers has not been studied and reported before.Here, we investigate the role of ions in the thermoelectric response of different PEDOT derivatives. We observe surprisingly large increases in the thermo-induced voltage at high humidity levels, of up to several hundreds of µV/K, which is identifi ed as an ionic Seebeck effect. The ionic thermovoltage and its potential for improving the thermoelectric effi ciency in conducting polymers are discussed.Five different PEDOT derivatives of different electrical conductivities (measured at 10% RH, 300 K) are deposited on glass substrates including two gold electrode patterns separated by 1 mm: (i) PEDOT-Tos (thickness = 627 nm, σ = 15 200 S m −1 ) synthesized by using solution oxidative in situ polymerization, [ 18 ] (ii) PEDOT-PSS-DEG (4.75 µm, σ = 530 S m −1 ) obtained by the addition of 2 wt% of the secondary dopant diethylene glycol (DEG) [ 19 ] into the PEDOT-PSS dispersion, (iii) PEDOT-PSS (5.68 µm, σ = 14 S m −1 ) as the commercial water dispersion called Baytron P by H. C. Starck, (iv) PEDOT-PSSPSSNa (3.43 µm, σ = 0.08 S m −1 ) obtained by the addition of 2 wt% of PSSNa to the PEDOT-PSS dispersion, and (v) selfdoped PEDOT-S (116 nm, σ = 75 S m −1 ), in which the sulfonate dopant groups are covalently linked to the PEDOT chains. PEDOT-S has been synthesized in the lab. [ 20 ] PEDOT-Tos exhibits the highest electrical conductivity. PEDOT-Tos possesses a high density of conducting PEDOT chains (EDOT/sulfonate molar ratio is 2.7) packed in a paracrystalline structure. [ 18 ] In PEDOT-Tos, the tosylate moieties are the anions and balance the positive charges carried along the conducting polymer chains. The included ions are effectively immobile in the polymer; it is an electronic (hole) conductor. In PEDOT-S, the EDOT/sulfonate ratio is 1.
