Color combination of polythiophene films doped with three dye molecules for electrochromism

Abstract

The electrochromic polythiophene/dopants (PTh/dopants) films were synthesized by the electrochemical polymerization on fluorinated tin dioxide (FTO) coated polyethylene terephthalate (PET) electrode. The dopants include Ponceau 4R (P4R), Naphthol red G (NrG), Acidblue 74 (A74) and sodium dodecyl sulfate (SDS). The morphologies, electrochemical, optical and spectroelectrochemical performance of the films were studied. The morphological analysis of the PTh/dopants films indicated that the surface roughness (SR): SRPTh/A74-SDS < SRPTh/NrG-SDS < SRPTh/P4R-SDS. The result of the electrochemical analysis indicated that the existence of each P4R, NrG, or A74 with SDS, had an outstanding synergy effect on the electrochemical stability of films. The study of optical analysis indicated that the polaron and bipolaron were formed in PTh chains. In addition, in all PTh/dopants films, the fully doped states were observed and the energy bandgaps were reduced. The result of spectroelectrochemical analysis indicated that the PTh films with the dopant (simultaneous use of the surfactant and each dye molecule) showed excellent electrochromic characteristics, optical properties and electrochemical stability. For example, the color contrast of PTh/P4R-SDS at oxidized λmax was 52%, while this data in control sample (PTh/ClO4−) was 22%. Furthermore, the anodic and cathodic coloration efficiency of PTh/dye-SDS is 5–6 times higher than that of PTh/ClO4−. Therefore, these results confirmed that decreasing the dimension of dye molecule and increasing its number of anions as dopant played an important role in improving the electrochemical and electrochromic performance of the films.