In-Situ Photoelectron Spectroscopy Study on the Air Degradation of PEDOT:PSS in Terms of Electrical and Thermoelectric Properties

Abstract

Despite excellent electrical and mechanical properties, practical application of poly(3,4-ethylenedioxythiophene) polymerized with poly(4-styrenesulfonate) (PEDOT:PSS) face the challenge of ensuring air stability in electronic industry. Here, degradation mechanism of PEDOT:PSS-based films in air is clearly demonstrated through X-ray/ultraviolet photoelectron spectroscopy (XPS/UPS) and its depth-profiling technique. As the duration of air-exposure increases, the PEDOT:PSS-based films alter molecular structures with the formation of S-O(x)bond in PEDOT and C-N(x)bond growth, changing ratios of insulating part (PSS-, PSSH, oxidized PEDOT) to conducting part and deteriorating their electrical conductivities. These transition behaviors are similar in all PEDOT:PSS-based films regardless of additives such as dopant or multi-walled carbon nanotube. Additionally, methanol treatment to various PEDOT:PSS-based films for inducing conformational change between PEDOT and PSS molecules, partly restore the electrical properties of the denatured PEDOT:PSS films. Finally, thermoelectric properties of the PEDOT:PSS-based films are characterized by investigating the effects of air-aging and methanol treatment on electrical conductivities, Seebeck coefficients, and power factors. To sum up, this study provides a useful guideline for establishing a strategy to ensure air stability of PEDOT:PSS-based films by clarifying the degradation mechanism and property recovery methods.