Electrochromism in WO_3 Evaporated Films

The characteristics of WO_3-ECC display devices consisting of a SnO_2 : Sb-WO_3-liquid electrolyte-SnO_2 : Sb structure were investigated. The SnO_2 : Sb films (sheet resistance of 6-35Ω/□) were prepared by chemical spray deposition method at a substrate temperature of 600℃, and the WO_3 films were prepared by thermal evaporation at a pressure below 3×(10)^<-5>Torr. The liquid electrolytes (containing 10 vol.% glycerol) used were 1N H_2SO_4,1N MgCl_2,1N CdCl_2,1N SnCl_4 and saturated InCl_3,aqueous solution. For any liquid electrolyte, a blue color appears in the area of WO_3 film with the counter electrode positively biased. The optical transmission spectrum of colored WO_3 films shows a broad bottom around 9500 A. The injected charge per unit volume in films has a constant value for the ECC cells with saturated coloration under an applied voltage of 2.5V. For the electrolyte of 1N H_2SO_4,1N MgCl_2,1N CdCl_3,1N SnCl_4 and sat. InCl_3,the constant value were 1.12×(10)^3C/(cm)^3,1.26×(10)^3C/(cm)^3,0.79×(10)^3C/(cm)^3,1.08×(10)^3C/(cm)^3 and 0.8×(10)^3C/(cm)^3,respectively. From the assumption of double injection of cations and electrons, tungsten bronze M_xWO_3 were found to be H_<0.38>WO_3,Mg_<0.21>WO_3,Cd_<0.14>WO_3,Sn_<0.09>WO_3 and In_<0.09>WO_3,respectively. Bleaching of the ECC cells was also described.