High thermoelectric performance of spray-coated Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) films enabled by two-step post-treatment process

Herein, poly (3,4-ethylenedioxythiophene):poly (styrenesulfonate) (PEDOT:PSS) films with improved thermoelectric properties are fabricated via spray coating followed by a sequential, two-step post-treatment process with ethylene glycol (EG) and a methylammonium iodide (MAI) solution. The EG treatment greatly increases the electrical conductivity of the PEDOT-PSS film up to 1752.1 S cm⁻¹, with an unchanged Seebeck coefficient of 15–17 μV K⁻¹, while the optimal use of 0.05 M MAI in DMSO/DI water for the second step provides a high power factor of 122.3 μW m⁻¹ K⁻², along with an increased conductivity of 2226.8 S cm⁻¹ and Seebeck coefficient of 22.8 μV K⁻¹. Notably, the obtained power factor is among the highest reported for spray-coated polymer-based thermoelectric devices. The performance enhancement is attributed to phase separation of the non-conductive PSS from the PEDOT, the change in chain conformation, the preferential orientation of the PEDOT crystallites, and the manipulation of energy levels. High thermoelectric performance of the as-fabricated PEDOT:PSS on a plastic substrate is established by using a facile proof-of-concept thermoelectric generator to generate a maximum power density of 12.1 nW cm⁻². The fabrication approach developed herein provides an essential paradigm for the production of polymer thermoelectric materials with great potential for application in wearable thermoelectric devices.