Thermoelectric Properties and Thermal Stability of PEDOT:PSS Films on a Polyimide Substrate and Application in Flexible Energy Conversion Devices

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In this study, we investigated the flexibility and thermal stability of films consisting of a complex of poly(3,4-ethylenedioxythiophene) (PEDOT) and polystyrene sulfonic acid (PSS) cast onto a polyimide substrate. We also prepared a PEDOT:PSS-based flexible device for thermoelectric energy conversion. The thermal stability of a PEDOT:PSS film was evaluated by measuring the Seebeck coefficient (S) and electrical conductivity (σ) for 30 heating and cooling cycles at 330 K to 380 K. Furthermore, the durability of the PEDOT:PSS film was examined by heating at 353 K in air for 4000 h. The approximate values of S and σ were 14 μV K−1 and 600 S cm−1, respectively. These values were almost the same before and after repeated bending treatments (10,000 times, radius of curvature 10 mm). In addition, the S and σ values for the PEDOT:PSS film were nearly constant during the heating cycle treatments. In the durability test, σ gradually decreased with increasing heating time (7% at 300 h, 17% at 3600 h). Thus, it was found that PEDOT:PSS films have both flexibility and mechanical toughness as well as relatively good thermal stability in air up to 3600 h. The maximum electric power for the PEDOT:PSS-based flexible device was 0.334 μW at ΔT = 100 K. These results for the power-generating properties of the flexible device are consistent with values calculated from the properties of the constituent materials.