Highly Conductive PEDOT:PSS Thin Films with Two-Dimensional Lamellar Stacked Multi-Layers
Youngno Kim, Yunryeol Kim, Jung Hyun Kim
Abstract
Conjugated polymers are desired as organic electrode materials because of their functional properties such as solution process, low cost, and transparency. Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), in particular, shows the highest applicability, but its heterogeneous structure presents limitations in terms of electrical conductivity. In this study, a facile method to fabricate multi-layered thin films with higher ordered structures was developed. Through the etching process with H2SO4 and dimethyl sulfoxide(DMSO), the insulated rich-PSS was removed from the upper layer to improve its electrical properties and rearrange the PEDOT molecular structures. The thickness of PEDOT:PSS thin films was experimentally optimized to maximize the enhancement of carrier mobility via a layer-by-layer (LBL) process. The combined method, consisted of etching and the LBL process, showed the improvement of the charge carrier mobility from 0.62 to 2.80 cm2 V−1 s−1. The morphology and crystallinity of the ordered PEDOT:PSS structure were investigated by X-ray photoemission spectroscopy (XPS), Raman, and X-ray diffraction (XRD). As a result, two-dimensional lamellar-stacked PEDOT:PSS thin films were fabricated through the repetitive etching and LBL process. The optimized PEDOT:PSS thin film showed an excellent electrical conductivity of 3026 S cm−1, which is 3.8 times higher than that of the pristine film (801 S cm−1).