We report temperature dependence of electrical c o n d u c t i v i t y a n d t h e r m o p o w e r f o r p o l y ( 3 , 4ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) thin films post-treated using a combination of an organic polar solvent of ethylene glycol (EG) and transition metal chlorides. The pristine and post-treated PEDOT:PSS films are characterized by X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS), atomic force microscopy (AFM), Raman spectroscopy techniques, and Hall effect measurements. Structural changes are confirmed by crystallinity improvement and Raman shift of the PEDOT:PSS, which correlate with a significant enhancement in thermoelectric power factor. The large variation of electronic transport in these films post-treated with three different metal chlorides can be attributed to the complex contribution of different conduction pathways. Among post-treated films, the highest electrical conductivity and power factor are attained for the EG/1 M ZnCl 2 post-treated PEDOT:PSS film with 1979 S/cm and 132 μW/m K 2 at 375 K. In general, organic conductive polymers have very low thermal conductivity; a zT = 0.24 at 375 K could be attained by assuming a thermal conductivity of 0.2 W/m-K. These results indicate that a combination of polar organic solvent EG and metal chlorides to post-treat a PEDOT:PSS film is a promising approach to enhance the thermoelectric properties of the conductive polymers of PEDOT:PSS.

Thermoelectric materials capable of converting waste heat energy into electrical energy are enchanting for applications in wearable electronics and sensors by harvesting heat energy of the human body. Organic conducting polymers offer promise of thermoelectric materials for next-generation power sources of wearable devices due to their low cost in preparation, easy processing, low toxicity, low thermal conductivity, mechanical flexibility, light weight, and large area application. Generally, the pristine PEDOT:PSS film has low electrical conductivity, small Seebeck coefficient, and low thermal conductivity. The thermoelectric power factors of conducting polymers of p-type PEDOT:PSS films are considerably improved via synergistic effect by using ethylene glycol and reductants of EG/NaBH 4 or EG/NaHCO 3 . As such, the charge carrier concentration of PEDOT:PSS films is tuned. The synergistic effect might lead to enhanced variation of density of states at the Fermi level and hence enhanced Seebeck coefficient. The resulting PEDOT:PSS films were characterized by atomic force microscopy (AFM), Raman spectroscopy, and XPS spectroscopy. The electrical conductivity and Seebeck coefficient were measured between 325 and 450 K. The carrier concentration and mobility were obtained by Hall measurements. The pristine thin film treated with 0.05 M EG/NaHCO 3 solution exhibits the highest power factor of 183 μW m −1 K −2 at 450 K among these two series of films due to its significant enhanced Seebeck coefficient of 48 μV/K. The maximum output power of 121.08 nW is attained at the output voltage of 6.98 mV and the output current of 17.45 μA. The corresponding maximum power density is 98 μW/cm 2 for a power generation device made of four pairs of p-leg (EG/NaHCO 3 post-treated PEDOT:PSS) and n-leg (Cu 0.6 Ni 0.4 ) on the polyamide substrate with the size of 4 mm × 20 mm for each leg.

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