Temperature dependence of polarons in conductive PEDOT:PSS thin films

Abstract

Organic conductive polymer, Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), has been widely used as an important component in organic optoelectronic devices, and recently it emerged as a promising candidate for novel epsilon-near-zero (ENZ) materials. The presence of polarons and bipolarons, acting as charge carriers in conductive polymers, has a profound influence on the electrical and optical characteristics. In this work, pristine, ethylene glycol-treated (EG-treated hereafter) and acid-treated PEDOT:PSS films were prepared for temperature-dependent spectroscopy measurement to investigate the temperature sensitivity of materials. Spectral fitting method and decomposition of the imaginary part of the permittivity is employed to elucidate the temperature sensitivity of ENZ in thin films treated with various solutions. The pristine PEDOT:PSS film is sensitive to temperature changes (ENZ wavelength changes by 93 nm), while the acid-treated PEDOT:PSS film is less affected by temperature (polarons and bipolarons have been significantly improved, ENZ wavelength changes by 32 nm). Finally, band diagrams are utilized to illustrate the dynamics of polarons and bipolarons within three thin film systems upon temperature excitation, elucidating the underlying physical mechanisms of the thin film's temperature sensitivity. Our research provides a new insight into the study of ENZ photonics in organic materials and the development of temperature-related applications.