Electrochromic contrast enhancement of nanostructured poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate films by composition/morphology control

Abstract

Poly(3,4-ethylenedioxythiophene) (PEDOT) films have been electropolymerized from an aqueous micellar polyethylene glycol (PEG) based solution containing sodium poly(styrenesulfonate) (NaPSS) and lithium trifluoromethanesulfonate. On varying the NaPSS content in the electrode-position bath, two strikingly different nanostructured morphologies were obtained for ensuing PEDOT:PSS films and these have been correlated to the electrochemical and optical performance of the films. The films grown from the formulation with EDOT:NaPSS in a 1:3 weight ratio comprise of a nanoparticulate structure with a to date scarcely reported hexagonal structure. The film surface is also characterized by some unusual floral shapes encompassing elongated grains. TEM studies reveal that in the 1:3 film two dimensional (planar) PEDOT chains are stacked on top of each other with a vertical separation of 4.63 Å. On the other hand the film generated from a 1:1 solution shows a texture wherein a random segregation of PSS particles is seen and this adversely affects the electrochromic response of the film. The larger charge storage capacity (4.9 mC cm⁻²), better charge reversibility during coloration and bleaching, good electrochemical cycling stability up to 2500 cycles, higher electronic conductivity and a superior coloration efficiency of 233 cm² C⁻¹ at a photopic wavelength of 550 nm under ion intercalation levels of 0.058 to 1.2 mC cm⁻² shown by 1:3 film as compared to the performance of the 1:1 film are ramifications of fast ion movement promoted by the novel microstructure and the hexagonal modification which has rarely been achieved in PEDOT:PSS films.