Coloration Dynamics of Spin‐Coated MoO3 · n H 2 O Electrochromic Films Fabricated from Peroxo‐polymolybdate Solution

A very smooth amorphous molybdenum oxide thin film can be fabricated easily by a spin‐coating technique using a solution of peroxo‐polymolybdic acid, which is formed by the direct reaction of metallic molybdenum with hydrogen peroxide. Amorphous resulting from heating such a film at 80–150°C exhibited reversible electrochromism in an organic electrolyte solution. However, its electrochromic characteristics depended on the heating temperature. Coloration dynamics of films treated at various temperatures were investigated by a potential step method. When the film was treated at temperatures as high as 150°C, its coloration process was diffusion controlled, while the transient current observed with films treated at lower temperature did not obey the Cottrell‐type relationship. Such behavior is discussed in relation to the structural features of the amorphous films.