The studies related to electrochromic phenomena performed in the seventies were mainly aimed at the development of information displays. Such applications require sm211 electrode sizes, i.e. with active surface areas of between about 0.01 to 10 cm . The development of large information devices and chiefly smart windows require much larger switching areas. This paper deals with the influence of increasing the active surface area on the response time. The latter depends on both properties of the cell components (transparent conducting layer, electrochromic film, electrolyte and counter electrode) and structure of the cell (size, shape, gap, resistivity of the busbar). Experimental devices were constructed with given components and cell geometry. The effect of a series resistance arisen mainly from the cell size was investigated and explained by the effect of the additional series resistance on the response time of a diffusion-controlled process. The study indicates that the scaling-up of W03 devices will be limited by an increase of the response time with increasing active area.
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