One-step post-treatment boosts thermoelectric properties of PEDOT:PSS flexible thin films

Abstract

• High power factor of 64.4 µW m −1 K −2 is achieved in PEDOT:PSS films at 360 K. • 80 vol.% DMAC solution boosts the electrical conductivity from 5 to 964 S cm −1 . • 0.5 mol L −1 LAA improves the Seebeck coefficient from 18.7 to 25 µV K −1 . • Mott variable range hopping model explains the thermoelectric transport behavior. Developing high-performance poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) significantly widens the practical applications of flexible organic thermoelectric devices, while the water-based co-solvent dopants and/or post-treatments are still rarely studied so far. Here, we develop a one-step post-treatment to improve the power factor of PEDOT:PSS films by using a water-based solution, which is composed of co-solvent (polar solvent dimethylacetamide (DMAC) and deionized water) and organic reducing agent L-ascorbic acid (LAA). The 80 vol.% DMAC solution significantly boosts the room-temperature electrical conductivity of the films from 5 to 964 S cm −1 , while the Seebeck coefficient can be further enhanced from 18.7 to 25 µV K −1 by treating with 0.5 mol L −1 LAA, contributing to a significantly improved power factor of 55.3 µW m −1 K −2 . The boosted electrical conductivity is ascribed to the separated PEDOT and PSS phases triggered by the high dielectric constant and polarity of DMAC; while the improved Seebeck coefficient is attributed to the reduced oxidation degree of PEDOT from the reducing agent LAA, both confirmed by the comprehensive structural and morphological characterizations. Furthermore, a maximum power factor of 64.4 µW m −1 K −2 can be achieved at 360 K and the observed temperature-dependent electrical transport behavior can be well explained by the Mott variable range hopping model. Besides, a flexible thermoelectric device, assembled by the as-fabricated PEDOT:PSS films, exhibits a maximum output power of ∼23 nW at a temperature difference of 25 K, indicating the potential for applying to low-grade wearable electronics.