New solution route to electrochromic poly(acrylic acid)/WO3 hybrid film

Electrochromic tungsten oxide film was fabricated by a new soft chemistry r oute, in which the transparent conducting glass substrate was successively dip-coated with poly(acrylic acid (PAA) and ammonium tungstate solutions. T he as-coated composite layer of PAA/(NH4)(2)-WO4.H2O was dried at a low tem perature (100 degreesC), and the ammonium tungstate component was polyconde nsed by add treatment in 1 N HCl to form an electrochromic PAA/WO3 film. Tr ansmission electron microscopy showed that the PAA/WO3 film contains regula rly dispersed WO3 grains with an average size of similar to5 nm. According to the Auger depth profile analysis, the relative content of W, O, and C wa s quite homogeneous along the height of film. Depending on the concentratio n 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 o f the PAA/WO3 layer could easily be controlled. By using a 2.5 wt % PAA sol ution, an optimum electrochromic function was achieved with a coloration ef ficiency of similar to 38 cm(2)/C and a cycle life of >11 000 under operati on with Q = 12.5 mC/cm(2).