High-Performance PEDOT:PSS Flexible Thermoelectric Materials and Their Devices by Triple Post-Treatments

Searching an effective method to enhance the thermoelectric properties of flexible organic films can significantly widen the application of flexible thermoelectric devices. Tuning the microstacking structure and oxidation level can effectively optimize the thermoelectric properties of poly(3,4-ethylenedioxithiophene):poly(styrenesulfonate) (PEDOT:PSS) organic films. Here, we adopt triple post-treatments with formamide (CH₃NO), concentrated sulfuric acid (H₂SO₄), and sodium borohydride in sequence to engineer flexible PEDOT:PSS thermoelectric films. A high power factor of 141 μWm^-1 K^-2 at 25 °C has been obtained for the PEDOT:PSS film. Such a high power factor stems from the high σ (1786 Scm^-1) and S (28.1 μVK^-1) after post-treatment with CH₃NO, H₂SO₄, and NaBH₄ in order. The increased carrier mobility resulting from both the selective removal of excess insulating PSS within the films and the conformation transition after CH₃NO and H₂SO₄ treatments is responsible for the enhancement of σ, while the subsequent NaBH₄ treatment optimize the electrical properties (σ and S) by modulating the oxidation level. A homemade thermoelectric device has also been fabricated using the as-prepared flexible PEDOT:PSS films and had a high output power density of ∼1 μWcm^-2 with human arm as a heating source. This study indicates that flexible thermoelectric devices based on cheap conducting polymers have great potential in wearable electronics.