New Solution Route to Electrochromic Poly(acrylic acid)/WO₃ Hybrid Film

Electrochromic tungsten oxide film was fabricated by a new soft chemistry route, in which the transparent conducting glass substrate was successively dip-coated with poly(acrylic acid) (PAA) and ammonium tungstate solutions. The as-coated composite layer of PAA/(NH 4 ) 2 WO 4 · n H 2 O was dried at a low temperature (100 °C), and the ammonium tungstate component was polycondensed by acid treatment in 1 N HCl to form an electrochromic PAA/WO 3 film. Transmission electron microscopy showed that the PAA/WO 3 film contains regularly dispersed WO 3 grains with an average size of ∼5 nm. According to the Auger depth profile analysis, the relative content of W, O, and C was quite homogeneous along the height of film. Depending on the concentration of PAA coating solution (1.0−3.0 wt %), the thickness and tungsten oxide content of the film were found to vary; therefore, the electrode property of the PAA/WO 3 layer could easily be controlled. By using a 2.5 wt % PAA solution, an optimum electrochromic function was achieved with a coloration efficiency of ∼38 cm 2 /C and a cycle life of >11 000 under operation with Q = 12.5 mC/cm 2 .