Ultrafast-switching viologen-anchored TiO(2) electrochromic device (ECD) was developed by introducing Sb-doped SnO(2) (Sb(x)Sn(1-x)O(2), ATO) as counter electrode (CE), and the switching behavior of the fabricated ECD was investigated as a function of Sb-doping concentration. About 9-nm-sized Sb(x)Sn(1-x)O(2) (x = 0-0.3) nanoparticles were synthesized by a solvothermal reaction of tin (IV) chloride and antimony (III) chloride at 240 degrees C, and employed to fabricate 2.4-mu m-thick transparent CE. Working electrode (WE) was formed from the 7-nm-sized TiO(2) nanoparticle by a doctor blade method, and the thickness of the nanoporous TiO(2) electrode was 4.5 mu m. The phosphonated viologen, bis(2-phosphonylethyl)-4,4'-bipyridinium dibromide, was then adsorbed on the prepared films for the construction of the ECD. The response time was strongly dependent on the doping concentration of Sb in ATO, and the fastest switching response was observed at 3 mol%. At this composition, the coloration time was 5.7 ms, and the bleaching time was 14.4 ms, which is regarded as one of the best results so far reported. (C) 2009 Elsevier B.V. All rights reserved.