Effect of external salt addition on the structural, morphological and electrochemical properties of flexible PEDOT:PSS based LbL multilayered films

Abstract

This article concerns with the effect of external salt addition on the structural, morphological and electrochemical properties of linear poly(ethylene imine) (LPEI) and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) based LbL assembled films that is a cathodic color changing electrode for electrochromic device. For this purpose, cationic and anionic commercial polyelectrolytes (PEs) with/without 0.3 M NaCl were deposited on PET-ITO with automatized dip coating system. From QCM-D, it was found that the multilayer deposition became larger for LbL assembled films obtained from salt-free PEs. While the dissipation change (Delta D) of (LPEI/PEDOT:PSS)(10/NaCl) (150 x 10(-6)) exhibited relatively soft/flexible structure compared to the (LPEI/PEDOT:PSS)(10) (110 x 10(-6)), AD changes became more obvious during PEDOT:PSS adsorption. Furthermore, it was determined that the film thickness and surface roughness values were highly dependent on the number of deposited bilayers whereas they dropped with the addition of salt to LPEI. The root mean square roughness (R-q) of (LPEI/PEDOT:PSS)(10), (LPEI/PEDOT:PSS)(20) and (LPEI/ PEDOT:PSS)(40) were found to be 28 nm, 41.7 nm and 61.5 nm, respectively, while R-q of (LPEI/PEDOT:PSS)(20)(/NaCl) was 14.2 nm. All LbL mutilayered films had hydrophilic character and the average contact angle value of (LPEI/PEDOT:PSS)(20)(/NaCl) was found to be 66 degrees due to the presence of salt within the multilayers. In addition, ion transport rate increased if the external salt was added to PE. Concerning the salt effect on colorancy of LbL multilayers, all films showed reversible color changes between blue and transparent/pale blue and (LPEI/PEDOT:PSS)(20) exhibited darker blue in the colored state whereas (LPEI/PEDOT:PSS)(20/NaCl) had more translucent in the bleached state.