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

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 electrodeposition 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 A. 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.