Enhanced Thermoelectric Performance and Lifetime in Acid-Doped PEDOT:PSS Films Via Work Function Modification

In recent years, most of the works on p-type organic thermoelectrics have focused on improving the thermoelectric properties of poly(3,4-ethylene dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) through a sequential doping–dedoping process. However, the air-stability of thermoelectric parameters of these systems, which is essential for the realization of reliable devices, remains largely unexplored. In this study, poly(ethyleneimine)-ethoxylate (PEIE) acts as a work function modification agent and an encapsulation layer to improve the thermoelectric performance and air-stability of nitric acid (HNO3)-doped PEDOT:PSS films. The evaporation of HNO3 is responsible for a simultaneous decrease in electrical conductivity and an increase in the Seebeck coefficient leading to the degradation of the power factor. PEIE reduces the evaporation of HNO3 from PEDOT:PSS and increases the power factor from 72 to 168 μW m–1 K–2. After a week of exposure to air, the films show a power factor of 124 μW m–1 K–2, retaining 74% of its initial thermoelectric merits. These results underscore the importance of PEIE as a material for enhancing thermoelectric performance and air-stability in the development of polymer-based thermoelectrics.