Nanostructured tungsten oxide-poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) hybrid films:: Synthesis, electrochromic response, and durability characteristics

Nanostructured hybrid thin films of the system tungsten oxide-poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (WO3-PEDOT:PSS) were synthesized by first forming a tungsten-oxide layer by surfactant-assisted electrochemical method, followed by deposition of a PEDOT:PSS layer. The hybrid-film formation is primarily based on coulombic interactions between the surface hydroxyl groups of tungsten oxide and the positively charged centers on the polymer backbone; this has been confirmed by electron microscopy and X-ray diffraction. High-resolution transmission electron microscopy reveals that the tungsten-oxide host with a monoclinic unit cell resides along with the amorphous domains of PEDOT: PSS. The hybrid film, being a dual electrochrome, exhibits a much larger coloring efficiency (227 cm(2) C-1 at 600 nm), a higher redox activity (larger currents for ion ingress and egress are obtained within the same potential range), and, most importantly, a superior electrochemical cycling stability when compared to the neat polymer film. While the pristine polymer film lifts off irrevocably from the substrate upon 3000 cycles of coloring and bleaching, the hybrid film sustains about 5000 cycles, albeit with some changes in the nanoparticulate morphology, elemental composition, and development of some new artifacts on the film surface. (C) 2008 The Electrochemical Society.